[Federal Register Volume 85, Number 225 (Friday, November 20, 2020)]
[Rules and Regulations]
[Pages 74560-74593]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 2020-25844]
[[Page 74559]]
Vol. 85
Friday,
No. 225
November 20, 2020
Part III
Department of Transportation
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Federal Aviation Administration
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14 CFR Part 39
Airworthiness Directives; The Boeing Company Airplanes; Final Rule
Federal Register / Vol. 85 , No. 225 / Friday, November 20, 2020 /
Rules and Regulations
[[Page 74560]]
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DEPARTMENT OF TRANSPORTATION
Federal Aviation Administration
14 CFR Part 39
[Docket No. FAA-2020-0686; Product Identifier 2019-NM-035-AD; Amendment
39-21332; AD 2020-24-02]
RIN 2120-AA64
Airworthiness Directives; The Boeing Company Airplanes
AGENCY: Federal Aviation Administration (FAA), DOT.
ACTION: Final rule.
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SUMMARY: The FAA is superseding Airworthiness Directive (AD) 2018-23-
51, which applied to all The Boeing Company Model 737-8 and 737-9 (737
MAX) airplanes. AD 2018-23-51 required revising certificate limitations
and operating procedures of the Airplane Flight Manual (AFM) to provide
the flightcrew with runaway horizontal stabilizer trim procedures to
follow under certain conditions. This AD requires installing new flight
control computer (FCC) software, revising the existing AFM to
incorporate new and revised flightcrew procedures, installing new MAX
display system (MDS) software, changing the horizontal stabilizer trim
wire routing installations, completing an angle of attack (AOA) sensor
system test, and performing an operational readiness flight. This AD
also applies to a narrower set of airplanes than the superseded AD, and
only allows operation (dispatch) of an airplane with certain
inoperative systems if specific, more restrictive, provisions are
incorporated into the operator's existing FAA-approved minimum
equipment list (MEL). This AD was prompted by the potential for a
single erroneously high AOA sensor input received by the flight control
system to result in repeated airplane nose-down trim of the horizontal
stabilizer. The FAA is issuing this AD to address the unsafe condition
on these products.
DATES: This AD is effective November 20, 2020.
The Director of the Federal Register approved the incorporation by
reference of a certain publications listed in this AD as of November
20, 2020.
ADDRESSES: For service information identified in this final rule,
contact Boeing Commercial Airplanes, Attention: Contractual & Data
Services (C&DS), 2600 Westminster Blvd., MC 110-SK57, Seal Beach, CA
90740-5600; telephone 562-797-1717; internet https://www.myboeingfleet.com. You may view this service information at the
FAA, Airworthiness Products Section, Operational Safety Branch, 2200
South 216th St., Des Moines, WA. For information on the availability of
this material at the FAA, call 206-231-3195. It is also available on
the internet at https://www.regulations.gov by searching for and
locating Docket No. FAA-2020-0686.
Examining the AD Docket
You may examine the AD docket on the internet at https://www.regulations.govby searching for and locating Docket No. FAA-2020-
0686; or in person at Docket Operations between 9 a.m. and 5 p.m.,
Monday through Friday, except Federal holidays. The AD docket contains
this final rule, any comments received, and other information. The
address for Docket Operations is U.S. Department of Transportation,
Docket Operations, M-30, West Building Ground Floor, Room W12-140, 1200
New Jersey Avenue SE, Washington, DC 20590.
FOR FURTHER INFORMATION CONTACT: Ian Won, Manager, Seattle ACO Branch,
FAA, 2200 South 216th St., Des Moines, WA 98198; phone and fax: 206-
231-3500; email: [email protected].
SUPPLEMENTARY INFORMATION:
Discussion
Summary of NPRM
The FAA issued a notice of proposed rulemaking (NPRM) to amend 14
CFR part 39 and supersede AD 2018-23-51, Amendment 39-19512 (83 FR
62697, December 6, 2018; corrected December 11, 2018 (83 FR 63561)) (AD
2018-23-51). AD 2018-23-51 applied to all Boeing Model 737-8 and 737-9
(737 MAX) airplanes. The NPRM proposed to apply only to the 737 MAX
airplanes identified in Boeing Special Attention Service Bulletin 737-
31-1860, dated June 12, 2020, which identifies line numbers for
airplanes with an original airworthiness certificate or original export
certificate of airworthiness issued on or before the effective date of
the original Emergency Order of Prohibition. Airplanes that have not
received an original airworthiness certificate or original export
certificate of airworthiness on or before the date of the original
Emergency Order of Prohibition will have been modified to incorporate
the changes required by this AD prior to receiving an original, or
original export, airworthiness certificate.
The NPRM published in the Federal Register on August 6, 2020 (85 FR
47698). The NPRM was prompted by the potential for a single erroneously
high AOA sensor input received by the flight control system to result
in repeated airplane nose-down trim of the horizontal stabilizer. To
address this unsafe condition, the NPRM proposed to require installing
new FCC software, revising the existing AFM to remove the AFM revisions
required by AD 2018-23-51 and to incorporate new and revised AFM
flightcrew procedures, installing new MDS software, changing the
horizontal stabilizer trim wire routing installations, completing an
AOA sensor system test, and performing an operational readiness flight.
The NPRM also proposed to allow operation (dispatch) of an airplane
with certain inoperative systems only if certain more restrictive
provisions are incorporated into the operator's existing FAA-approved
MEL.
Related Actions
During September 2020, the FAA conducted an operational evaluation
of the operating procedures (checklists) in the proposed AD, to assess
their effectiveness. The FAA also evaluated pilot training proposed by
Boeing pertaining to the 737 MAX. The FAA conducted the evaluation
jointly with the Ag[ecirc]ncia Nacional de Avia[ccedil][atilde]o Civil
(ANAC) Brazil, Transport Canada Civil Aviation (TCCA), and the European
Union Aviation Safety Agency (EASA). This joint evaluation is referred
to as the Joint Operational Evaluation Board (JOEB). The operational
evaluation included airline pilots with varied levels of experience
from the United States, Canada, Brazil, and the European Union. The FAA
and the other civil aviation authorities (CAAs) concluded that air
carrier pilots operating the 737 MAX need to complete special training
on the 737 MAX, including ground and flight training in a full flight
simulator (FFS). The FAA also identified additional special emphasis
areas to be included in 737 MAX recurrent or continuing qualification
pilot training.
The FAA documented the results of the JOEB evaluation in the draft
FAA Flight Standardization Board (FSB) Report, The Boeing Company 737,
Revision 17 (draft 737 FSB Report). As described in an addendum to the
draft 737 FSB Report, the JOEB evaluation identified three areas in the
proposed Airspeed Unreliable checklist for potential refinement.\1\ On
October 6, 2020, the FAA made the draft 737 FSB Report and the Addendum
available to the public for comment (85 FR 63641,
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October 8, 2020). The comment period closed November 2, 2020.
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\1\ These areas are described in the 737 FSB Report Addendum,
which is in the docket for this rulemaking.
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The FAA issued the final FSB Report, The Boeing Company 737,
Revision 17, dated November 16, 2020 (final 737 FSB Report), after
considering the relevant comments received to the 737 FSB Report docket
(Docket No. FAA-2020-0928). The FAA considered the conclusions of the
JOEB, comments received during the NPRM comment period regarding the
AFM procedures, and comments received during the draft 737 FSB Report
comment period in determining the final AFM procedures contained in
this final rule. For information on the refinements to AFM procedures
identified in the proposed AD, please refer to the section of this
preamble titled, ``Suggestions for Crew Procedure Changes.''
Additionally, the FAA has also finalized the ``Preliminary Summary
of the FAA's Review of the Boeing 737 MAX,'' dated August 3, 2020,
which the FAA placed in the docket at the time of publication of the
NPRM. This ``Summary of the FAA's Review of the Boeing 737 MAX,'' dated
November 18, 2020, is also included in the docket for this rulemaking.
The final Summary includes additional explanation regarding 737 MAX
design changes, certification efforts, maintenance considerations,
pilot training, and final disposition of the Technical Advisory Board
(TAB) findings. The TAB is an independent team of experts that
evaluated efforts by the FAA and efforts by Boeing associated with the
redesign of the maneuvering characteristics augmentation system (MCAS).
The conclusions from the TAB and resolution of the findings directly
informed the FAA's decision-making on MCAS.\2\ The TAB included FAA
certification specialists and chief scientific and technical advisors
not involved in the original 737 MAX certification program. TAB members
also included subject matter experts from the U.S. Air Force, the Volpe
National Transportation Systems Center, and the National Aeronautics
and Space Administration. All findings that the TAB members identified
as required for return to service of the 737 MAX were resolved to their
satisfaction.
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\2\ The TAB Report has been included in this docket.
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Summary of Final Rule
After careful consideration of the comments submitted \3\ and
further review of the proposal, the FAA adopts this final rule. This
final rule mandates corrective action that addresses an unsafe
condition on the 737 MAX. This unsafe condition is the potential for a
single erroneously high AOA sensor input received by the flight control
system to result in repeated airplane nose-down trim of the horizontal
stabilizer, which, in combination with multiple flight deck effects,
could affect the flightcrew's ability to accomplish continued safe
flight and landing.
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\3\ In developing this final rule, the FAA considered comments
submitted to the NPRM docket and also comments submitted to the 737
FSB Report docket.
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As proposed in the NPRM, the corrective actions mandated by this AD
include a revision of the airplane's flight control laws (software).\4\
The new flight control laws now require inputs from both AOA sensors in
order to activate MCAS. They also compare the inputs from the two
sensors, and if those inputs differ significantly (greater than 5.5
degrees for a specified period of time), will disable the Speed Trim
System (STS), which includes MCAS, for the remainder of the flight and
provide a corresponding indication of that deactivation on the flight
deck. The new flight control laws now permit only one activation of
MCAS per sensed high-AOA event, and limit the magnitude of any MCAS
command to move the horizontal stabilizer such that the resulting
position of the stabilizer will preserve the flightcrew's ability to
control the airplane's pitch by using only the control column. This
means the pilot will have sufficient control authority without the need
to make electric or manual stabilizer trim inputs. The new flight
control laws also include FCC integrity monitoring of each FCC's
performance and cross-FCC monitoring, which detects and stops erroneous
FCC-generated stabilizer trim commands (including MCAS).
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\4\ In the NPRM, the FAA used several terms (including ``new,''
``updated,'' and ``revised'') when describing the FCC software
(including MCAS and control laws) required by paragraph (g) of this
AD. This software change is a complete replacement of the original
FCC software, including a new part number. This final rule requires
installation of the same FCC software as described in the NPRM and
refers to it as the new FCC software, new MCAS, and new control
laws. For example, where this final rule uses the term ``new MCAS,''
this term reflects the same meaning as ``revised MCAS'' or ``updated
MCAS'' used in the NPRM.
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This AD further mandates changes to the airplane's AFM to add and
revise flightcrew procedures to facilitate the crew's ability to
recognize and respond to undesired horizontal stabilizer movement and
the effects of a potential AOA sensor failure.
This AD also mandates an AOA DISAGREE alert, which indicates
certain AOA sensor failures or a significant calibration issue. The
alert is implemented by revision of MDS software; as a result, certain
stickers (known as INOP markers) will be removed.
Additionally, this AD mandates adequately separating certain
airplane wiring, and conducting an AOA sensor system test and an
operational readiness flight on each airplane before the airplane is
reintroduced to service.
Finally, this AD requires that operators that wish to dispatch
airplanes with certain inoperative systems must first have incorporated
specific provisions that are more restrictive into their existing FAA-
approved MEL.
Differences From the NPRM
This final rule differs from the NPRM in minor respects. After
review of input from the operational evaluations and public comments,
the FAA adjusted two AFM procedures: The Airspeed Unreliable and the
ALT Disagree non-normal checklists. This AD simplifies and corrects
grammatical and typographical errors in the Airspeed Unreliable non-
normal checklist (figure 2 to paragraph (h)(3) of this AD), and revises
the ALT Disagree non-normal checklist (figure 8 to paragraph (h)(9) of
this AD) to correct a typographical error in the NPRM.
The FAA has reviewed and approved new and updated service
information that is mandated by this AD, including Boeing Alert
Requirements Bulletin 737-22A1342 RB and Alert Service Bulletin 737-
22A1342, both dated November 17, 2020, for the new FAA-approved FCC
software; Boeing Special Attention Service Bulletin 737-31-1860,
Revision 1, dated July 2, 2020, for the MDS software change; and Boeing
Special Attention Service Bulletin 737-27-1318, Revision 2, dated
November 10, 2020, for the horizontal stabilizer wiring change. This AD
also provides credit for accomplishment of certain prior actions as
specified in paragraph (o) of this AD.
Public Comment
The FAA provided the public with an opportunity to comment on the
proposed AD and received approximately 230 submissions to Docket No.
FAA-2020-0686. The FAA received comments from individual commenters as
well as from organizations. The majority of the comments were from
individuals.
Organizations submitting comments included the Families of
Ethiopian Airlines Flight 302; the civil aviation authorities of Turkey
(Turkish DGCA) and the United Arab Emirates (UAE GCAA); the National
Transportation Safety Board (NTSB); the National Air
[[Page 74562]]
Traffic Controllers Association (NATCA); Flyers Rights; Aerospace
Safety and Security, Inc.; the Aerospace Safety Research Institute,
Inc.; Boeing; Airlines for America (A4A); the Ethiopian Airlines Group;
the Joint European Max Operators Group (JEMOG); the British Airline
Pilots Association (BALPA); the Allied Pilots Association; the
Association of Flight Attendants-CWA (AFA-CWA); Air China; Ameco;
Travelers United, Inc.; Southwest Airlines Pilot Association (SWAPA);
and the Air Line Pilots Association, International (ALPA).
The following summarizes the comments received on the NPRM, and
provides the FAA's responses.
A. Support for the NPRM
The FAA received supportive comments on the NPRM from Travelers
United, Inc., and numerous other commenters. Commenters who expressed
support for the NPRM noted the benefits of the proposed design changes
based on lessons learned and applied by the FAA, the resolution of
issues related to the airplane's MCAS, the relative ease of
accomplishing the proposed changes, a general appreciation for the
airplane design and handling, and the length and intensity of the
review of the unsafe condition, corrective action, and the airplane,
which the commenters said resulted in a safe design. The NTSB expressed
general support for the NPRM as it relates to MCAS, noting ``positive
progress on meeting the intent of the overall recommendation regarding
system safety assessments (SSAs) for the Boeing 737 MAX relating to
uncommanded flight control inputs.''
B. Fundamental Design/Approach Concerns
The Boeing 737 MAX uses MCAS to change the handling characteristics
for the flightcrew in order to comply with certain regulations during
high-AOA maneuvers. In the NPRM, the FAA proposed to require the
installation of new FCC software with new MCAS control laws to replace
the earlier FCC software installed on 737 MAX airplanes. Several
commenters questioned the fundamental design of the airplane,
especially the inclusion and availability of MCAS.
Comments Regarding Inclusion and Availability of MCAS
Comment summary: Several commenters stated that MCAS should not be
retained as a function on the airplane, and other commenters including
the Families of Ethiopian Airlines Flight 302 had fundamental concerns
with the basic design and availability of MCAS. More specifically,
these comments focused on the availability of MCAS after failure,
whether the airplane remained safe and compliant, and on the redundancy
of the system and its inputs.
FAA response: The FAA determined that the 737 MAX with the new MCAS
implemented by the new FCC software, as proposed in the NPRM and
required by paragraph (g) of this AD, meets FAA safety standards.
The MCAS on the 737 MAX improves the pilot handling qualities
(maneuvering characteristics) during non-normal flight conditions,
specifically when the airplane is at high AOAs. During normal flight,
the 737 MAX should never be at an AOA high enough to be within the
range that MCAS would activate. FAA regulations require that airplanes
be designed and tested over the entire range of potential angles of
attack, including high AOAs. FAA regulations also require column force
to increase as AOA increases (14 CFR 25.143(g), 25.251(e), and 25.255).
In a 737 MAX, if a pilot is maneuvering the airplane with the flaps
retracted and encounters a high AOA (outside of the normal flight
envelope), MCAS will activate and command the stabilizer to move in the
airplane nose-down direction, which changes the handling
characteristics such that the pilot would need to pull with increasing
force on the control column to maintain the current AOA or further
increase the AOA. MCAS-commanded stabilizer movement results in
increased column forces such that the airplane meets FAA handling
characteristics requirements for airplane operation at high AOAs.
Existing FAA regulations (14 CFR 25.21, 25.671, and 25.672) allow for
use of stability augmentation systems (such as MCAS) in showing
compliance with FAA handling characteristics requirements. The 737 MAX
airplane with MCAS operative is therefore compliant.
To be approved by the FAA, the proposed designs of transport
category airplane flight control systems must comply with applicable 14
CFR part 25 regulations. The assessment of compliance must consider the
airplane in the as-designed, fully operational configuration (no
failures) and also, in accordance with 14 CFR 25.671 and 25.1309, in
potential failure conditions. When assessing those failure conditions,
the applicant must take into account both the probability of the
failures and their airplane-level consequences. The outcome must show
that the airplane is capable of continued safe flight and landing after
single failures and any failure combination not shown to be extremely
improbable (14 CFR 25.1309). For example, a twin-engine transport
airplane complies with all regulations while both engines are
operating, but if there is a single engine failure, the airplane must
be capable of continued safe flight and landing with only the one
remaining engine operating.
With MCAS inoperative, the Boeing 737 MAX is capable of continued
safe flight and landing and is therefore compliant with 14 CFR 25.671
and 25.1309. If at high AOAs, with MCAS inoperative, MCAS will not move
the stabilizer, and the resultant incremental change in column force
will not be experienced by the pilot. In this situation, the pilot
maintains control and can decrease the airplane's AOA by moving the
column forward. Through comprehensive analysis, simulation testing, and
flight testing, the FAA determined that the airplane meets applicable
14 CFR part 25 standards, with MCAS operative and with failures,
including failures that render MCAS inoperative. With MCAS inoperative
after a failure, the 737 MAX is capable of continued safe flight and
landing, as required by 14 CFR 25.671 and 25.1309.
If a system must be functional at all times to ensure continued
safe flight and landing, the system must be available to function after
a single failure. Conversely, if an inoperative system does not prevent
continued safe flight and landing, then it is acceptable under FAA
regulations for the system to not be available after a single failure;
this is how MCAS is implemented on the 737 MAX.
The foregoing discussion focuses on an inoperative MCAS. All
failure modes must be considered and assessed by the manufacturer and
the FAA for compliance with 14 CFR 25.671 and 25.1309. The new MCAS is
designed such that most failures will result in the MCAS function
becoming inoperative, with maintenance required before a subsequent
flight to return MCAS to being fully operative and available. The
manufacturer and the FAA have assessed potential failure modes of the
system to ensure that no single failure will prevent continued safe
flight and landing and that any combination of failures that could
occur in service, except for those shown to be extremely improbable,
would similarly not prevent continued safe flight and landing.
Failures of MCAS are annunciated to the flightcrew. MCAS is
implemented as part of the airplane's STS. During flight, STS failures
(including MCAS failures) are annunciated by illumination of the master
caution light, the SPEED TRIM FAIL light, and the system annunciator
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panel (FLT CONT). Per training, the flightcrew will follow applicable
crew procedures for continued safe flight and landing.
Based on analyses, simulation, and flight testing to establish
consequences of failures and the capability for continued safe flight
and landing, the FAA has determined that the new MCAS meets FAA safety
standards, and that it is acceptable for STS (including MCAS) to remain
inoperative for the remainder of a flight after the system fails.
Therefore, the additional redundancy requested by commenters, to
increase the availability of the system, is not required.
C. Specific Concerns About MCAS
1. Comments Regarding Redundancy of Two AOA Sensors
Comment summary: The Families of Ethiopian Airlines Flight 302
asked whether the two AOA sensor inputs to MCAS are truly redundant.
FAA response: The two AOA sensors and the data they provide are
independent, and are therefore redundant in that the failure of one AOA
sensor does not impede the operation of the other AOA sensor. For MCAS
inputs, the left and right air data/inertial reference units (ADIRUs)
receive direct input from the AOA sensors installed on the left and
right sides of the airplane, respectively. Each ADIRU transmits the
current AOA sensor position to the left and right FCCs via databuses.
The signal path to each FCC is independent of the other FCC (e.g., the
left AOA data does not travel through the left FCC to reach the right
FCC).
2. Comments Regarding Additional AOA Sensors or Data
Comment summary: Numerous commenters including the Families of
Ethiopian Airlines Flight 302 and BALPA contended that three or more
AOA values are required for the system to be able to continue operating
after a failure of a single AOA sensor. Commenters assert that if the
two AOA values diverge, the system cannot detect which value is
erroneous; but with three AOA inputs, if one value deviates from the
other two, the deviant value could be excluded while the system
continues to operate using data from the remaining two sensors. In
support of their requests for additional AOA sensors or inclusion of a
derived value (synthetic AOA), some commenters noted that AOA sensors
are exposed to the elements or other external factors such as bird
strikes.
FAA response: As explained earlier in this preamble, the 737 MAX is
capable of continued safe flight and landing with MCAS inoperative.
Accordingly, continued safe flight and landing can be accomplished when
MCAS is disabled following the failure of a single AOA input. The new
MCAS, as proposed in the NPRM and mandated by this AD, utilizes two AOA
inputs and compares the difference between them. If there is a
significant difference (greater than 5.5 degrees for a specified period
of time), then MCAS will be disabled (unavailable) for the remainder of
that flight, annunciation will alert the flightcrew to the failure, and
maintenance will be required before subsequent flight.
Regarding exposure to the elements (that is, weather conditions but
not a bird strike), AOA sensors are designed, tested, and qualified for
their operational environment as part of certification (14 CFR
25.1301). The new MCAS design accounts for safe operation after AOA
sensor failures due to environmental causes including bird strikes that
bend or break the vane of the AOA sensor, as discussed in subsequent
responses.
3. Comments Regarding Keeping MCAS Partitioned
Comment summary: Commenters suggested that MCAS be partitioned such
that each FCC would receive input from only a single AOA sensor, with
the pilots responsible for switching control from one FCC to the other.
FAA response: The change suggested by the commenters would not
improve the safety of the airplane, because it would remove the AOA
sensor comparison feature of the new design and allow a single AOA
sensor failure to activate MCAS as in the original MCAS. Regarding the
request to make the pilots responsible for switching control from one
FCC to the other, the FAA evaluated the design presented by the
applicant. It is likely, however, that the commenters' proposal would
increase pilot workload and may also introduce unreasonable reaction
time requirements for pilot actions. Contrary to the commenters'
proposed single-input configuration, which could allow for MCAS
activation following a single failure, the new MCAS design mandated by
this AD addresses the unsafe condition by not allowing for that exact
event.
4. Comments Regarding MCAS Response After Failure(s)
Comment summary: Several commenters, including BALPA and the
Turkish DGCA, requested that the FAA require that MCAS not activate if
there is a disagreement between AOA sensor inputs or a dual AOA sensor
failure, and that MCAS should not remain available following certain
AOA sensor failures.
FAA response: The FAA confirms that most AOA sensor failures will
result in the MCAS function becoming inoperative, and if MCAS is
activated, it will activate only once for each high-AOA event, which
does not preclude continued safe flight and landing. AOA sensor
failures can be divided into two broad categories: (1) Detected
failures of the electrical circuit that measures the angular position
of the AOA sensor such that the AOA data is labeled as invalid and not
used by user systems (including MCAS); and (2) undetected failures that
do not damage the electrical circuit such that AOA data is transmitted
from the ADIRU to the FCC as valid. Both 737 MAX accidents involved the
second category of AOA sensor failures; the AOA sensor electrical
circuit was unaffected and therefore perceived by the ADIRU to be
valid, and the transmitted value was used by the MCAS function in the
FCC.
With the new MCAS, the second type of AOA sensor failure will
result in disparate inputs to the FCCs. When disparate inputs are
received by the FCCs, the FCCs will disable the MCAS function,
preventing it from activating for the remainder of that flight. When
MCAS is disabled in this way, the master minimum equipment list (MMEL)
does not allow for dispatch of the airplane again until the system is
repaired.
If a single AOA sensor is damaged due to a bird strike, the bent or
broken AOA sensor vane will affect the AOA measurement. If the AOA
sensor vane breaks off, the AOA sensor will provide a high AOA value
due to a counterweight falling within the sensor. With a significant
difference between valid AOA sensor inputs, the FCCs will disable MCAS.
Later, if the other AOA sensor is damaged (resulting in a high AOA
value), MCAS will already have been disabled and there will be no MCAS
activation. The sequential failure of two AOA sensors during the same
flight is unlikely; even more unlikely would be a case where two
sensors are damaged simultaneously and symmetrically such that there is
not a difference sensed between the two AOA sensors as they both
transition to similar high AOA values. Even if such a simultaneous and
symmetrical failure were to occur, MCAS would activate only once. The
FAA confirmed through testing and analysis during certification that a
single activation of MCAS will not prevent continued safe flight and
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landing. The pilots can control the change in pitch using only the
control column, or trim inputs, or any combination of the two.
The other concern raised by these commenters was that if during a
flight there is a detected AOA sensor circuit failure (the first
category described previously), MCAS will continue to be available to
operate with only a single AOA sensor input for the remainder of that
flight. During the remainder of the flight when the first circuit
failure occurred, a subsequent independent failure of the other AOA
sensor, that is not detected (second category, e.g., a bird strike) and
results in an erroneous valid AOA input, would be extremely improbable.
Nevertheless, if this failure combination were to occur (first category
followed by the second category), the outcome would not prevent
continued safe flight and landing; MCAS would activate only one time,
with the pilots able to control the airplane using either the control
column, the electric trim switches, or both. This scenario was analyzed
and tested by FAA engineers and pilots and found to be compliant with
the FAA's safety standards.
5. Comments Regarding MCAS Operation at Low Altitude
Comment summary: A commenter stated that MCAS should not operate in
certain phases of flight, such as takeoff, climb, and landing, because
there should not be a potential for a failure to cause the airplane to
lose altitude during those phases of flight. Another commenter
suggested MCAS should not operate at low altitudes due to the potential
for a wake turbulence encounter or a bird or animal strike.
FAA response: MCAS is functional only during flight with the flaps
fully retracted. When the airplane is at low altitudes near the airport
for takeoff, and later during approach and landing, flaps are extended,
typically below 1,000 feet; therefore, MCAS is not operational for the
take-off and landing phases of flight. For other phases of flight
including climb, AOA disagreement due to an incident such as a bird
strike will be detected by the FCCs, and the FCCs will disable MCAS for
the remainder of that flight. Since the new MCAS function is consistent
with the commenters' requests, no change to this AD is necessary.
6. Comments Regarding MCAS Availability for Multiple Activations
Comment summary: Two commenters expressed concern that limiting
MCAS to a single activation would render MCAS unavailable for more
activations later in the flight, if needed, and that MCAS would not be
available to perform its intended function.
FAA response: The commenters' concerns do not accurately reflect
the new MCAS functionality. The new MCAS is designed to activate one
time for each high-AOA event (above the MCAS activation threshold). The
new MCAS will activate when there is a high-AOA event (above activation
threshold as previously described), and then will reset after the
airplane returns to a low AOA that is sufficiently below the MCAS
activation threshold, such that it will be available for a subsequent
activation if there is a subsequent high-AOA event. As a result, after
the new MCAS activates once, it will be available for more activations
later in the same flight. Only if there has been a failure during the
flight that disables MCAS, which is indicated by the SPEED TRIM FAIL
light, will MCAS not be available during a high-AOA event with the
flaps retracted.
7. Comments Regarding Disabling of Column Cutout Switches
Comment summary: Two commenters suggested changing the design and
function of the column cutout switches on the 737 MAX to be more
similar to those on earlier Boeing Model 737 designs.
FAA response: The column cutout switch function of earlier Boeing
Model 737 models would not allow for MCAS activation.
Column cutout switches on earlier Boeing Model 737 models allow the
flightcrew the capability to interrupt (cut out) a stabilizer command
in one direction by making a control column input in the other
direction (e.g., an airplane nose-down stabilizer command will be
interrupted by pulling the control column aft). The 737 MAX has the
same column cutout feature, but it is temporarily disabled during the
short duration of an MCAS activation.
MCAS operates only during high-AOA events, which are typically
caused by the flightcrew pulling aft on the control column. To allow
MCAS to operate as intended, the FCC temporarily disables the column
cutout switches when MCAS is activated (makes a command). Without this
temporary disable feature, the MCAS command to move the stabilizer in
the airplane nose-down direction would otherwise be interrupted by the
column cutout switches.
After the MCAS activation, the column cutout switches revert to a
configuration where control column inputs will interrupt stabilizer
commands in the opposite direction. When MCAS is not making a command,
the column cutout switches operate like they do on earlier models of
the Boeing Model 737. It is only during the short duration of an MCAS
command that the column cutout switches on 737 MAX airplanes operate
differently than those on other Boeing Model 737 airplanes.
The new MCAS includes cross-FCC monitoring, which detects and stops
erroneous FCC-generated stabilizer trim commands (including MCAS). This
protects against an erroneous FCC-generated stabilizer trim command
throughout the entire flight, including when the column cutout switches
are temporarily disabled.
8. Comments Regarding Erroneous MCAS Enable Command
Comment summary: A commenter expressed concern that the MCAS enable
command, which disables column cutout, could be asserted during a
horizontal stabilizer trim runaway due to hardware faults on the
stabilizer interface.
FAA response: The scenario set forth by the commenter would result
from the simultaneous occurrence of an erroneous FCC-generated command
that disables the column cutout feature and an erroneous command (from
either the pilot or the FCC) to move the stabilizer. The potential for
this combination of failures to occur simultaneously is mitigated by
integrity monitoring of the MCAS enable command by the new FCC
software, which monitors for proper FCC performance. Furthermore,
periodic maintenance checks, implemented by new tasks in the Boeing 737
Maintenance Planning Document (MPD), verify the function of the cutout
switches (located on the aisle stand) and the MCAS enable command.
Finally, the cross-FCC monitor also reduces the likelihood of any FCC-
generated stabilizer trim runaway command.
9. Comments Regarding MCAS Vulnerability to Single Failures
Comment summary: A commenter stated that the system should not be
vulnerable to a single failure, and expressed concern that the new MCAS
remains vulnerable to a single failure. Another commenter asked whether
there is a scenario where any single failure, or probable combination
of failures, requires the flightcrew to stop moving the stabilizer by
grabbing the manual stabilizer trim wheel in the flight deck; this
commenter also asked whether that is in the crew procedure.
FAA response: The FAA determined that the new MCAS is compliant
with 14 CFR 25.671 and 25.1309, such that no single failure, or
combination of
[[Page 74565]]
failures not shown to be extremely improbable, will prevent continued
safe flight and landing. Nevertheless, the AFM revisions required by
this AD include a runaway stabilizer procedure with guidance for
arresting any potential runaway stabilizer event. The final step of
that procedure is to ``grasp and hold stabilizer trim wheel.'' That
procedure is yet another layer of protection.
10. Comments Regarding MCAS Vulnerability to Sinusoidal AOA Input
Comment summary: Several commenters expressed concern about
perceived vulnerabilities of the new MCAS implemented by the new FCC
software. A commenter expressed concern that MCAS is vulnerable to
sinusoidal AOA sensor input. Another commenter expressed concern that
the middle value select (MVS) function implemented to mitigate
erroneous sinusoidal AOA sensor input as part of the new MCAS can
diverge or cause a limit cycle oscillation. Another commenter expressed
a concern with the MVS algorithm, specifically that if there is a fixed
offset between the two AOA sensor values that is less than the 5.5-
degree threshold that will cause deactivation of MCAS, the MCAS
function would be utilizing AOA sensor inputs that are offset by up to
5.5 degrees.
FAA response: The new FCC software compares the two AOA sensor
inputs relative to each other and will disable STS (including MCAS) for
the remainder of the flight if the difference between the two exceeds a
threshold of 5.5 degrees. The new MCAS also uses an MVS algorithm to
address the potential for a sinusoidal AOA input from a single AOA
sensor. To demonstrate compliance with 14 CFR part 25 standards, the
new MCAS was analyzed and tested with various failure scenarios,
including a sinusoidal AOA sensor input. The results established that
MVS is effective, that it will not result in divergence or limit cycle
oscillation, and that the design is compliant and safe. The FAA also
tested the new MCAS with the scenario of AOA sensors offset by up to
5.5 degrees during certification and found the design to be compliant
and safe.
11. Comments Regarding MCAS Vulnerability to Pilot Induced Oscillation
Comment summary: A commenter expressed concern about the MCAS
response to a pilot induced oscillation (PIO).
FAA response: PIO, which is also known as airplane/pilot coupling
(APC), is a phenomenon where the frequency of pilot inputs couples
(matches) with an inherent airplane frequency. The susceptibility of
the 737 MAX to PIO/APC was assessed throughout all of the FAA flight
testing during certification of the 737 MAX. The FAA found the 737 MAX
is not prone to PIO/APC. This remains true with and without MCAS being
available. This also remains true during a valid or erroneous MCAS
activation.
12. Comments Regarding Adequacy of MCAS
Comment summary: A commenter was concerned that the new MCAS is
inadequate with regard to the rate at which it can respond during a
high-AOA event. The commenter noted that the rate at which the airplane
AOA increases may be too great for MCAS to be effective.
FAA response: MCAS has been analyzed and tested by the FAA and the
manufacturer in various scenarios and flight conditions, which includes
MCAS's rate of response, as part of the certification process, and was
found to meet its intended function, and to be compliant with all
applicable 14 CFR part 25 regulations.
D. Specific Concerns About Alerting
1. Comments Regarding Annunciating MCAS Activation and MCAS Failures
Comment summary: Numerous commenters, including BALPA, the Families
of Ethiopian Airlines Flight 302, and Ethiopian Airlines Group,
commented regarding annunciations and alerting associated with MCAS.
Some commenters wanted the system changed to add features to make the
pilot aware when MCAS is making a valid command to the stabilizer
system. They were concerned that without annunciation, pilots would
have difficulty discerning normal from non-normal MCAS activation. They
suggested illuminating a new light, displaying a message on the primary
flight display (PFD), displaying a new flight mode annunciator,
displaying the magnitude of the incremental MCAS command to the
stabilizer, and generating a voice annunciation. Other commenters
suggested that MCAS failures or deactivations be annunciated by the
addition of a warning to alert the crew, a red MCAS FAIL warning, or a
loud alert at the same time MCAS is disabled.
FAA response: The new MCAS already alerts the pilot of an MCAS
failure. The addition of more annunciation of valid MCAS activation is
not necessary to address the unsafe condition.
When the STS (including the speed trim function and the MCAS
function) makes a command to move the stabilizer, the flightcrew is
aware of the command because the manual trim wheels, located in the
aisle stand between the two pilots in the flight deck, will rotate as
the stabilizer moves. The STS has been a basic design feature of the
Boeing Model 737 series for many years and is familiar to flightcrews.
It is not necessary for a system to annunciate to the pilot that it is
active. The pilot can both see and hear the manual trim wheels rotate
when the stabilizer is moved. Normal MCAS activation occurs only during
non-normal flight conditions when the airplane is at a high AOA, and
high AOA maneuvering could potentially already be a high workload
scenario for the flightcrew. Indications to the pilot that the airplane
is at a high AOA include the appearance of the amber band on the
airspeed tape, the appearance of amber pitch limit indicator (PLI),
flashing amber airspeed digits on the airspeed tape, the appearance of
the red and black barber pole on the airspeed tape on the PFD,
increasing column force, and stick shaker.
Additional annunciation of normal MCAS function during this time
could distract the pilots from recovering from this non-normal high-AOA
flight condition.
Regarding the commenters' request for annunciation of FCC failures
related to MCAS, the system alerts the flightcrew by illuminating the
Master Caution, system annunciator panel (FLT CONT), and SPEED TRIM
light. After landing, the SPEED TRIM FAIL and/or STAB OUT OF TRIM light
will be illuminated. Therefore, the existing system already alerts the
flightcrew to MCAS failures.
The new FCC software monitors inputs and outputs for failures,
including erroneous MCAS commands, and will disable MCAS for detected
failures. During normal operation, the FCC commands horizontal
stabilizer movement only for three cases: (1) When the autopilot is
engaged and the stabilizer is moved to offload column movement, (2) as
part of the speed trim function during manual flight, associated with
changes in airspeed, and (3) as part of the MCAS function during manual
flight at high AOA outside normal flight conditions. Pilots will learn
about automated stabilizer trim operation in the special 737 MAX
training. Pilots have the ability to override any FCC-generated
stabilizer trim command, because pilot stabilizer trim commands via the
thumb switches
[[Page 74566]]
on the control wheel always have priority over FCC-generated commands.
Finally, if the flightcrew deactivates MCAS by moving the
stabilizer trim cutout switches (located on the aisle stand) to the
cutout position using the Runaway Stabilizer NNC (non-normal
checklist), there is no associated annunciation. When the FCC generates
an STS command (speed trim or MCAS) after the trim cutout switches are
moved to the cutout position, the system will detect the lack of trim
motor response to the STS command and illuminate the master caution
light, the SPEED TRIM FAIL light, and the system annunciator panel (FLT
CONT). If the autopilot is engaged, when the FCC generates an autopilot
command after the trim cutout switches are moved to the cutout
position, the system will detect the lack of trim motor response to the
autopilot command and illuminate the STAB OUT OF TRIM light. Therefore,
the requested additional annunciation is not necessary.
2. Comments Regarding Display of AOA DISAGREE Alert
Comment summary: Several commenters, including the UAE GCAA,
requested that the AOA DISAGREE alert be displayed in the pilot's
primary field of view and/or on the Head Up Display (HUD).
FAA response: Paragraph (j) of this AD requires installation of new
MDS software including functionality to display the AOA DISAGREE alert
on each pilot's PFD if the left and right AOA values differ by more
than 10 degrees for more than 10 seconds. The PFDs are in the primary
field of view in front of each pilot, and are therefore consistent with
the commenters' request. Regarding the message also showing on the HUD,
the FAA notes that HUDs are optional equipment. For airplanes with HUDs
installed, updated HUD software will display AOA DISAGREE on the HUD if
it is being displayed on the PFD. The HUD software is not required by
this AD. No change to this AD is necessary based on this comment.
3. Comments Regarding Omission of AOA DISAGREE Alert From 737 MAX
Comment summary: Several commenters asked why the AOA DISAGREE
alert was not included in the original 737 MAX design.
FAA response: The AOA DISAGREE alert is a standard design feature
on the 737 NG fleet (600/700/800/900/900ER) and was intended to be
standard for the 737 MAX, but it was instead erroneously linked by the
manufacturer to an optional AOA indicator (which some refer to as a
gauge). The optional AOA indicator is a round dial that provides
graphic and numeric AOA position information on both PFDs. Because of
this error, only airplanes with the (optional) AOA indicator had a
functioning AOA DISAGREE alert. This was incorrectly implemented by the
manufacturer during the display software development, and was not
identified until after the 737 MAX entered into service.
4. Comments Regarding Display of AOA Indicators
Comment summary: Several commenters, including BALPA, suggested
that the optional AOA indicators (gauges) be made basic to the
airplane, or offered as a no-cost option, so they are available to
check accuracy and enhance pilot situational awareness. Another
commenter asked why there is no standby (third) AOA indicator.
FAA response: The AOA position indicators are not required for
compliance with design standards with regard to pilot situational
awareness. The cues to the pilots as the airplane approaches stall are
inherent in other airspeed and attitude information displayed on the
PFDs, which provide situational awareness and are described earlier in
this preamble. In response to the question about a third AOA indicator,
the FAA notes that there is no requirement to have any AOA indicator
for compliance with 14 CFR part 25 standards.\5\ The FAA has not
changed this AD based on this comment.
---------------------------------------------------------------------------
\5\ This preamble addresses elsewhere a comment suggesting the
addition of a third independent AOA input, which would be required
to provide data to a third independent AOA indicator.
---------------------------------------------------------------------------
5. Comments Regarding Additional Aural Alerts
Comment summary: A commenter stated that the AOA DISAGREE alert, as
well as IAS DISAGREE and ALT DISAGREE alerts, need a corresponding
aural alert for immediate two-sense awareness of the condition by the
flightcrew.
FAA response: The AOA DISAGREE, IAS DISAGREE, and ALT DISAGREE
alerts show on both PFDs in the pilots' primary field of view. This
design has been assessed, tested, and found compliant with 14 CFR part
25. The FAA has not changed this AD based on this comment.
E. Specific Concerns About Crew Interface
1. Comments Regarding Flightcrew Maintaining Control of Airplane
Comment summary: Numerous commenters stated that the pilot must be
able to maintain control of the airplane. A commenter expressed concern
that MCAS remains vulnerable to a combination of MCAS commands and
pilot inputs that would generate the repetitive MCAS activations that
occurred during the accident flights. The commenters requested that the
FAA ensure that the pilots have the physical strength required to make
column inputs to counter system failures. These commenters stated that
the system design should be changed to include an independent means to
turn MCAS off via a dedicated MCAS shutoff switch, which would be
different from and independent of the aisle stand cutout switches. The
commenters suggested including a guard that would illuminate the MCAS
shut-off switch when MCAS is inoperative and provide a corresponding
aural warning.
FAA response: None of the identified additional system changes are
necessary to achieve the objective that the flightcrew must be able to
maintain control of the airplane. The new MCAS design and associated
pilot procedures and training focus on the pilot's ability to control
and remain in control of the airplane.
The new MCAS has several features to ensure that the pilot
maintains control. With the new MCAS design, pilot inputs to the trim
switches do not reset MCAS. Therefore, the new MCAS is not vulnerable
to the same repetitive cycles of MCAS activation that occurred during
the accident flights.
The new MCAS design will (1) detect failures and not command MCAS
if those failures occur; (2) result in only a single activation of MCAS
for certain dual failures; and (3) in the event the airplane
experiences multiple high AOA events, it will limit the stabilizer
movement so the pilot can always maintain control of the airplane using
only the control column.
The FAA also notes that the Runaway Stabilizer NNC (as revised and
required by paragraph (h) of this AD) is a means for a pilot to stop
MCAS commands and any electric command to the stabilizer trim motor.
That procedure is another safety feature in the unlikely event the
airplane experiences erroneous stabilizer trim movement.
Regarding the comments suggesting a dedicated switch to disable
MCAS to include a guard, light, or aural warning, the FAA notes that
when MCAS is
[[Page 74567]]
disabled due to detected faults, the Master Caution and system
annunciator panel (FLT CONT), as well as the SPEED TRIM light on the P5
overhead panel, will be illuminated. The new MCAS is compliant with 14
CFR part 25 certification standards and addresses the unsafe condition,
so it is not necessary to change the design to add a dedicated switch
to disable MCAS or add an additional light or aural alert.
2. Comments Regarding Function of Aisle Stand Cutout Switches
Comment summary: Numerous commenters suggested changing the design
of the aisle stand stabilizer trim cutout switches to resemble the
design on pre-MAX versions of Model 737 airplanes. On those earlier
Model 737 airplanes, two guarded switches on the aft end of the center
aisle stand, aft of the throttle levers, are used to stop electric
commands to the stabilizer trim motor. The pilots are directed to use
the switches by two NNCs: Runaway Stabilizer and Stabilizer Trim
Inoperative. In both procedures, the pilot is directed to ``place both
STAB TRIM cutout switches to CUTOUT.'' On the earlier models of the
Boeing Model 737, the switches have distinct functions (labeled
``main'' and ``auto'') where one (auto) would cut out all FCC-generated
stabilizer commands (autopilot and speed trim) and the other (main)
would cut out pilot-generated commands (from the pilot thumb switches).
On the 737 MAX, however, the switches are wired in series, and both
perform the same function (primary and backup): To cut out all electric
commands to the stabilizer (both FCC-generated commands and pilot
commands). The commenters asserted that the configuration of the
earlier (pre-MAX) Boeing Model 737 airplanes would allow the pilot to
disable MCAS commands while retaining the ability to make electric trim
inputs using the thumb switches. The commenters expressed concern that
pilots would be required to use manual trim for the remainder of that
flight.
FAA response: No change to the design or this AD is necessary to
address the commenters' concerns. The new MCAS has redundancy (receives
inputs from two AOA sensors and is implemented by two FCC computers)
and will automatically disable MCAS for the remainder of the flight if
certain failures are detected. For detected failures where MCAS stops
making commands, the pilot does not use the aisle stand cutout
switches, and retains the ability to use thumb switches to control the
stabilizer. The only time the thumb switches would be unavailable is if
the pilot moves the aisle stand cutout switches to the cutout position;
in that event, the pilot has the option to use manual trim to move the
stabilizer. As discussed in the next paragraph, manual trim forces have
been assessed and deemed acceptable.
3. Comments Regarding Manual Trim Forces
Comment summary: Many commenters, including the Allied Pilots
Association, ALPA, BALPA, Ethiopian Airlines Group, and the UAE GCAA,
expressed concerns regarding the 737 MAX manual trim system and the
forces required to control and trim the aircraft following a failure of
the STS (including MCAS). Some questioned the mechanical advantage
provided by the manual trim system and whether it had been evaluated in
flight testing. A commenter stated that it takes 15 turns of the pitch
trim wheel to get just one degree of horizontal stabilizer movement,
and some pilots may lack the strength to make those turns if the
required force is too high. The commenter suggested pilots should be
required to take a yearly strength test to determine whether they are
capable of pulling a yoke or turning the pitch trim wheel in simulated
emergency conditions.
FAA response: Following the Ethiopian Airlines accident, the 737
MAX manual trim system design and force requirements were an area of
intense focus by the Ethiopian Aircraft Accident Investigation Bureau,
the FAA, Boeing, and other CAAs, which continued throughout the FAA's
evaluation and testing of the new FCC software and new MCAS during
certification. The data from the Ethiopian Airlines accident indicates
that the high trim wheel forces experienced during that accident were
the result of significant horizontal stabilizer mis-trim combined with
excessive airspeed. The new FCC software limits the maximum mis-trim
that could occur for any foreseeable failure of the STS, thus ensuring
the pilot can maintain control of pitch using the column only, without
requiring exceptional pilot skill, strength, or alertness.
Additionally, the FAA evaluated the manual trim system for the unlikely
event that manual trim will be necessary. This included detailed
analysis of manual trim wheel forces as a function of both dynamic
pressure and out-of-trim state, testing to measure and assess the
strength capability of an anthropometric cross-section of male and
female subjects, and FAA flight testing to quantitatively validate
manual trim wheel forces and qualitatively evaluate the ability to
control the airplane for continued safe flight and landing. These
flight test conditions and the associated analysis included maximum
out-of-trim conditions well beyond those possible for any failure
conditions in the new MCAS design and included the most critical
aircraft configurations and airspeeds to the operational airspeed limit
of the flight envelope (referred to as Vmo/Mmo). The FAA determined
that manual trim wheel forces meet FAA safety standards and do not
require exceptional pilot skill or strength nor any special or unique
handling techniques as suggested by some of the commenters.
Improvements to the Runaway Stabilizer non-normal procedure proposed in
the NPRM and mandated by this final rule include steps to help ensure
column forces remain manageable and reduce manual wheel trim forces in
the unlikely case where manual trim may be needed. Additionally, this
AFM procedure and pilot training emphasize the first priority in an
emergency is to maintain control of the airplane, and also include
specific information about the manual trim system including techniques
for effectively using manual trim. Therefore, the FAA has made no
changes in finalizing this AD related to the manual trim system or
related AFM non-normal procedures.
4. Comments Regarding Availability of Automation After MCAS Failure
Comment summary: A commenter stated that the autopilot and
autothrottle should be available following an MCAS failure. The
commenter expressed concern that MCAS will be triggered routinely due
to turbulence and gusts during cruise, and its shutdown would render
the autopilot inoperative. The commenter noted that when autopilot is
not available, airplanes are prohibited from flight at higher altitudes
where airplanes fly with reduced vertical separation minima (RVSM).
FAA response: In most cases, autopilot and autothrottle are
available following an MCAS failure. Flight testing of the new MCAS has
demonstrated that it will not be triggered due to turbulence and gusts.
The new MCAS design is such that following certain MCAS failure
scenarios, the system will allow for engagement of the autopilot and
autothrottle. Flightcrew training and procedures identify when the
flightcrew may attempt to engage the autopilot and/or autothrottle. If
the Runaway Stabilizer NNC is used, the use of autopilot is prohibited
by the procedure.
[[Page 74568]]
5. Comments Regarding Selection of Air Data Source
Comment summary: A commenter wanted the air data system to be
revised to allow for selection of offside data if onside data is
erroneous (i.e., the captain can select to display first officer's
data, or vice versa), and ideally to automate it to prevent the display
of erroneous data.
FAA response: This comment regarding the air data system is not
related to the unsafe condition addressed by this AD. The Boeing 737
air data system is federated such that independent air data (altitude,
airspeed, and AOA) from the captain's side is used to provide
information on the captain's PFD, while independent air data from the
first officer's side is used to provide information on the first
officer's PFD. The unsafe condition addressed by this AD concerns a
single high erroneous AOA generating repetitive MCAS behavior, which,
in combination with multiple flight deck effects, could affect the
flightcrew's ability to accomplish continued safe flight and landing.
The requirements of this AD address the MCAS issue.
6. Comments Regarding Suppression of Overspeed Warning
Comment summary: A commenter stated that the warning system needs
to be revised so that the overspeed aural warning can be suppressed
manually by the flightcrew.
FAA response: This comment is not related to the unsafe condition
addressed by this AD. Like the airspeed and stick shaker, the overspeed
aural warning is federated in a left/right configuration aligning with
the captain's and first officer's sides of the airplane. The system
meets the certification standards applicable to this airplane and was
certificated without a provision for suppressing the aural warning.
7. Comments Regarding Crew Procedure To Extend Flaps
Comment summary: Two commenters suggested adding a crew procedure
to extend the flaps in the event of an MCAS failure. They noted that
MCAS is available only when the flaps are retracted, which indicates
that the airplane does not need MCAS when the flaps are extended.
FAA response: It is not necessary to add a new flightcrew procedure
for extending the flaps in order to counter an MCAS failure. With the
new MCAS design, time-critical crew procedures are not required to
mitigate MCAS failures. Furthermore, extending the flaps at high
airspeeds could damage the flaps and cause controllability problems.
The FAA has not changed this AD regarding this issue.
F. Suggestions for Crew Procedure Changes
1. Comments Regarding AFM Crew Procedure Adequacy
Comment summary: Several commenters, including BALPA, NATCA, ALPA,
Boeing, the Allied Pilots Association, the JEMOG, Ethiopian Airlines
Group, A4A, and SWAPA, requested that the FAA modify the emergency and
non-normal procedures contained in the proposed AD. These comments
covered several of the proposed checklists, with an emphasis on the
Airspeed Unreliable and Runaway Stabilizer checklists. The comments
included requests to make small changes involving typographical errors,
to add information to checklists, to simplify checklists, to shorten or
reduce the number of memory items, and to develop checklists for
certain specific failure cases. Three commenters, including BALPA and
Ethiopian Airlines Group, recommended providing a combined Airspeed
Unreliable and Runaway Stabilizer checklist for certain specific
failure conditions.
Finally, ALPA commented that, while it supported in principle the
potential changes to the Unreliable Airspeed checklist described in the
addendum to the draft 737 FSB Report, it cannot provide support or
opposition to any such changes without reviewing the checklist as
modified. ALPA proposed that the FAA release the final Airspeed
Unreliable Checklist for public review and comment after modification
with the potential refinements described in the addendum.
FAA response: The FAA has made several changes to the checklists,
taking into consideration not only comments provided in the context of
the NPRM, but also in response to the outcomes from the FAA FSB
evaluation. The inputs from the FAA FSB were the result of
collaboration with other CAAs during the JOEB. The JOEB conducted an
extensive evaluation of the proposed procedures and training conducted
by a wide variety of crews, including line pilots with levels of
experience ranging from high to low and regulatory pilots from four
separate CAAs during the NPRM comment period.
The AFM procedures specified in the proposed AD were the result of
procedural development conducted by FAA test pilots, human factors, and
operations personnel (along with other engineering and operational
experts from other CAAs and from Boeing), which considered a myriad of
similar aspects as the procedures were developed and evaluated.
Additionally, the procedures were evaluated during FAA certification,
including human factors evaluations to determine compliance to 14 CFR
25.1302, and system safety assessments to determine compliance to 14
CFR 25.1309. The FAA convened a team of test pilots, operational
pilots, and human factors experts during the development of the AFM
procedures specified in the proposed AD. The FAA convened a similar
team to consider each procedural comment made during the NPRM comment
period and to determine if changes were warranted to improve safety.
A4A and SWAPA expressed concern that there are too many recall
items in the Runaway Stabilizer non-normal procedure, and included a
suggestion for how to reduce the number of steps. The suggestion
included combining some recall items to achieve fewer numbered steps,
but with multiple embedded actions in each recall item, such that the
suggested changes would result in the same number of required
flightcrew actions. The FAA agrees that it is desirable to minimize
recall items when appropriate. The recall steps in the non-normal
procedures required by paragraph (h) of this AD reflect flightcrew
actions required to address a runaway stabilizer condition. Based on
the FAA's evaluation and in coordination with human factors
specialists, the FAA determined that the commenters' proposed changes
would complicate the recall steps and would increase the likelihood
that a critical flightcrew action is forgotten or missed. The FAA
considered all of the commenters' requests in the context of crew
workload, clarity of instruction, consistency with training objectives,
and consistency with other procedures contained in the AFM. The FAA
declines the request to combine checklists because checklists must be
applicable to all potential failure conditions, not just the specific
failure conditions noted by the commenters. Additionally, the failure
conditions where a combined checklist might be useful were evaluated by
multiple flightcrews, resulting in a conclusion by the FAA that,
primarily due to the new MCAS required by this AD, the order and
content in which these two checklists were accomplished is not critical
to continued safe flight and landing.
The FAA made minor changes to the procedures that were proposed in
the NPRM. The changes simplify and
[[Page 74569]]
correct grammatical and typographical errors in, the Airspeed
Unreliable non-normal checklist (figure 2 to paragraph (h)(3) of this
AD) as follows:
Removed the words ``using performance tables from an
approved source,'' which contradicted the next sentence.
Corrected a typographical error to specify actions if the
``captain's and first officer's altitude indications are both
unreliable'' instead of the proposed ``captain's or first officer's
altitude indications are both unreliable.''
Revised a note to correct a typographical error; the
corrected text refers to ``DA/MDA,'' while the previous text referred
to ``DH/MDA,'' and revised the last sentence for clarity.
Revised a sentence to specify that the pitch bar may
``automatically'' be removed, thus clarifying that removal does not
require pilot action.
Revised a sentence to specify ``An AFDS pitch mode''
instead of ``Selection of an AFDS pitch mode.''
Added a note to specify ``only use flight director
guidance on the reliable PFD.''
The FAA also revised the ALT Disagree non-normal checklist (figure
8 to paragraph (h)(9) of this AD) to correct a typographical error in
the proposed AD. The corrected text refers to ``DA/MDA,'' while the
proposed text referred to ``DH/MDA.''
To the extent that ALPA suggests the addendum contained
insufficient information to provide a meaningful comment, the FAA notes
that the addendum identified the areas of potential checklist
refinement and the reasons why refinement may be necessary. The JOEB's
operational evaluation of the proposed checklists generated potential
refinements that did not result in any substantive change to the
checklists proposed in the NPRM. Rather, the results of the evaluation
indicated that minor revisions to the unreliable airspeed checklist,
which are reflected in this AD, may be appropriate. As such, there was
no need for the FAA to publish the ``final checklist'' with the 737 FSB
Report. However, because the FAA was aware that additional information
obtained during the operational evaluation could have an impact on the
final checklists, it provided notice of the findings in an addendum to
the 737 FSB Report and sought comment from the public. The FAA finds
that the addendum provided sufficient information for commenters to
assess the potential revisions and offer alternatives to the proposed
checklist to address the concerns suggested by the operational
evaluation.
2. Comments Regarding Crew Procedure To Disable Stick Shaker
Comment summary: Several commenters, including the Allied Pilots
Association, ALPA, BALPA, Ethiopian Airlines Group, and the UAE GCAA,
expressed concerns regarding the attention-getting nature of the stick
shaker and requested a change to the procedures to include a means to
suppress an erroneous stick shaker, including procedures to pull the
associated stick shaker circuit breaker. In contrast, a commenter
expressed a concern with the possible safety risks of including a
procedure to pull the stick shaker circuit breaker in order to silence
the warning.
FAA response: The FAA infers that the commenters are suggesting
there is an unacceptably high flightcrew workload when stick shaker is
activated erroneously. The 737 stall warning/stick shaker is, by
design, attention getting and can be a distraction during an
erroneously high-AOA event. However, after careful evaluation, the FAA
has not changed the AFM non-normal procedure to include pulling the
stick shaker circuit breakers in this final rule, for the following
reasons.
The FAA evaluated all failure conditions of the new FCC software as
part of certification of the proposed system changes. The new FCC
software removes the potential for repeated, uncommanded MCAS inputs in
the presence of an erroneous high AOA sensor input. This new design
therefore removes the most significant contributor to unacceptably high
flightcrew workload. With the new FCC software on the 737 MAX, the FAA
tested and assessed all remaining flight deck effects, including
erroneous stick shaker, during all foreseeable failure conditions,
including high-AOA sensor failures during the most critical phases of
flight (such as during takeoff or go-around). With the remaining flight
deck effects and associated crew workload, these failures and effects
were found compliant and safe.
The FAA considered the commenters' concerns that an erroneous stick
shaker may pose a distraction for the crew, and evaluated that scenario
with procedures that include steps to silence an erroneous stick shaker
stall warning via a circuit breaker pull. The FAA finds that an
erroneous stick shaker, while it may pose a distraction to the
flightcrew, does not affect controllability of the airplane. The stick
shaker circuit breaker locations also do not meet FAA requirements for
convenient operation for emergency controls for the complete range of
pilots from their normal seated position in the flight deck, leading to
possible distraction from their primary duties to safely control and
monitor the aircraft. Furthermore, inclusion of these additional steps
would add cognitive and physical workload to an already substantial
Airspeed Unreliable non-normal procedure, and errors in locating and
pulling the correct circuit breaker may lead to other airplane hazards.
Balancing the concerns associated with adding a procedure to pull
circuit breakers against the distraction of an erroneous stick shaker,
the FAA has concluded that the design is compliant and safe, and
therefore no change to the proposed non-normal procedures related to
silencing the 737 MAX stall warning is required for this AD.
3. Comments Regarding Changes Associated With Crew Procedures
Comment summary: The FAA received comments from A4A, JEMOG, Air
China, Ameco, and several other commenters regarding the new AFM non-
normal procedures that were primarily administrative in nature rather
than specific recommended changes. A commenter recommended referring to
the AFM non-normal procedures as ``updates'' versus ``new'' as stated
in the NPRM. Another commenter stated that the proposed new non-normal
procedures were different and more complicated than previous Boeing
Model 737 non-normal procedures. Another commenter disagreed with the
FAA's proposed allowance to insert the figures containing the non-
normal procedures directly into the AFM. A4A expressed concern with the
memory items in the proposed AFM non-normal procedures and use of Quick
Reference Cards (QRCs) by some operators. Finally, a commenter
requested that the FAA assess the proposed procedures in light of one
pilot instead of a crew of two.
FAA response: While it is true that some of these non-normal
procedures can be viewed as updates to existing procedures, such as
those in the operator's Quick Reference Handbook, this AD addresses AFM
non-normal procedures that are part of the required type design change
to the 737 MAX. The FAA is mandating removal of old, and replacement
with new, AFM non-normal procedures. These AFM changes will result in
corresponding changes to flightcrew training and operations materials
including applicable Quick Reference Handbook Non-Normal Checklists
such that they reflect these new AFM procedures.
Regarding the comment about the added complexity in the new AFM
non-normal procedures compared to
[[Page 74570]]
previous Boeing Model 737 procedures, as previously noted the AFM
procedures specified in the proposed AD were thoroughly vetted by the
FAA and others, as previously described in the ``Related Actions''
section. The AFM procedures are required by this AD as part of the 737
MAX design changes; their complexity has been reduced during the FAA's
certification activity, and they have been validated by the FSB during
the JOEB evaluation.
To facilitate immediate incorporation of new AFM non-normal
procedures, the FAA allows for copies of the figures to be inserted
directly into the existing AFM if needed. That provision is specified
in paragraph (h) of this AD. The FAA agrees that revised AFMs should be
provided to operators, and the FAA expects those revisions will be
available from Boeing following issuance of this final rule.
The FAA did not assess use of QRCs, which are operator specific.
Should an operator wish to use QRCs that deviate from the AFM
procedures specified in paragraph (h) of this AD, the operator must
coordinate with its principal inspector or responsible Flight Standards
Office and submit a request for an alternative method of compliance
(AMOC) to the requirements of this AD.
Finally, while most tasks in the flight deck could be accomplished
by a single pilot, the FAA notes that the 737 MAX is certified with two
pilots as the minimum crew, in accordance with 14 CFR 25.1523.
No change to this AD is necessary based on these comments.
4. Comments Regarding Disabling Elevator Feel Shift
Comment summary: A commenter requested that the flight control
system disable differential feel in the event it is triggered falsely
by an erroneous high AOA condition.
FAA response: The FAA infers the commenter is referring to the
Elevator Feel Shift (EFS), which is associated with identification of a
stall on 737 NG and 737 MAX airplanes based on AOA sensor data.
Although both MCAS and EFS use AOA data, only MCAS can move the
horizontal stabilizer. The EFS changes control column feel force, but
does not use the horizontal stabilizer trim system to initiate the
changed feel force. This comment is unrelated to MCAS and the unsafe
condition addressed by this AD. The FAA considered this system during
the analysis, flight testing, and human factors assessments performed
prior to approval of the new MCAS implemented by the FCC software
required by paragraph (g) of this AD. No change to this AD is necessary
based on this comment.
5. Comments Regarding Timeliness of Flightcrew Procedures
Comment summary: Boeing recommended that the FAA revise a sentence
in the sixth paragraph of the Proposed Design Changes section of the
NPRM to clarify the use of ``timeliness'' as it relates to the
flightcrew performing a non-normal procedure. Boeing stated that there
is an element of timeliness expected in flightcrew responses to all
non-normal events.
FAA response: The FAA intentionally referred to the ``timeliness''
of the flightcrew performing a non-normal procedure in the proposed AD.
The 737 MAX flight control design at the time of the Lion Air and
Ethiopian accidents relied on pilot use of secondary flight controls
(i.e., the electric trim switches) in a particular way (large
continuous commands versus several short duration commands) or use of
the Runaway Stabilizer non-normal crew procedure (using aisle stand
cutout switches or grasping the manual trim control wheel), in a
relatively short amount of time, for certain failure conditions
(erroneous MCAS command) to retain aircraft control and ensure
continued safe flight and landing. Control of the airplane during this
failure scenario depended on these timely crew actions. With the new
MCAS implemented by the FCC software required by this AD, basic control
of the airplane is ensured for all potential failure conditions through
the use of only the primary flight controls (i.e., control column),
without the need for particular and timely pilot reactions on non-
primary controls. Therefore, the FAA has determined that no change to
this AD is warranted.
G. Suggestions Regarding Monitors/Maintenance/Operations
1. Comments Regarding AOA Sensor Checks and Monitoring
Comment summary: Several commenters offered input regarding
suggested additional checks and monitoring of the AOA sensors,
including doing a visual inspection before flight, continuously
monitoring the AOA sensor electrical circuits, comparing AOA sensor
values before flight, and continuously monitoring them throughout the
flight. The commenters asked whether the monitors can detect damage
(e.g., damage that occurs while at the gate) to an AOA sensor while on
the ground. The commenters noted that the NPRM did not mention ground
operations actions regarding vulnerable AOA vanes. The commenters
requested expansion of the one-time AOA sensor system test (required by
paragraph (l) of this AD) to a regularly scheduled repetitive action
(not just one time before the airplane is returned to service).
FAA response: The vane-style AOA sensor used on the 737 MAX is a
common instrument installed on many transport airplanes. The existing
preflight walk-around inspection of the airplane includes a visual
check of the condition of the AOA sensors. These AOA sensors include
electrical circuits that measure the angle of the sensor. The position-
sensing electrical circuits are continuously monitored and can detect
if an electrical circuit is compromised. The AOA sensors also include
electrical heaters in the body of the sensor and within the vane that
aligns with local airflow and rotates within the sensor as AOA changes.
The electrical current to the AOA heaters is monitored to detect a
heater failure. The left and right AOA sensor values are not compared
before flight because AOA sensors can be moved by winds. The left and
right AOA sensor values are compared during flight and before the data
is used by MCAS. If the difference between them is more than 5.5
degrees, MCAS will be disabled. If an AOA sensor is damaged while at
the gate, the typical damage would be a bent or broken vane. This
damage could be detected during the preflight inspection. If the heater
circuit is damaged, the heater failure will be annunciated. If a vane
is bent only a small amount, there may be small differences between the
captain's and first officer's altitude and airspeed indications.
Paragraph (l) of this AD requires a one-time check of the AOA sensors
to verify that the AOA sensors are calibrated correctly and the AOA
heaters are working properly. Scheduled checks of the AOA sensors are
not necessary due to the preflight inspections, the continuous circuit
monitors, and the pilots' use of altitude and airspeed data affected by
the AOA sensors.
2. Comments Regarding AOA Sensor Calibration and Testing
Comment summary: A commenter requested improved calibration and
testing of critical AOA sensors.
FAA response: The Collins Aerospace Component Maintenance Manual
(CMM) that is used for calibrating the 737 MAX AOA sensors as they are
assembled has been updated with a new final check to verify that the
AOA sensor has been calibrated correctly. This new check uses a simple
independent electrical test that will
[[Page 74571]]
detect whether the more sophisticated calibration equipment was
configured and used correctly. The AOA sensor is tested on the airplane
using the AOA sensor system test in the AMM. This test is specified in
Boeing Special Attention Service Bulletin 737-00-1028, dated July 20,
2020, which is required by paragraph (l) of this AD. The test is
required to ensure that all 737 MAX AOA sensors are properly calibrated
and the heaters are operational prior to return to service. Therefore
no change to this AD is necessary based on this comment.
3. Comments Regarding Discerning AOA Sensor Failures
Comment summary: The Turkish DGCA, Ethiopian Airlines Group, and
other commenters proposed to integrate information from the various AOA
sensor electrical circuits and other data available on the airplane to
establish when there is an AOA sensor failure and when data from the
AOA sensor should not be used. Data from the Ethiopian Airlines Flight
302 accident shows a detected AOA heater failure coincident with the
sensed AOA transitioning rapidly to a large AOA value.\6\ The
commenters also noted that with the failure of the AOA sensor heater,
the AOA sensor is more vulnerable to icing and consequently could
provide unreliable AOA output values. Proposed scenarios that would
cause AOA sensor data to be disregarded include the following: Heater
failure, heater failure combined with a rapid change in the AOA sensor
position to a position consistent with vane departure, AOA disagree at
90 knots during takeoff, unreasonable AOA for flight conditions, and an
AOA that disagrees with the estimated (synthetic) AOA.
---------------------------------------------------------------------------
\6\ Figure 56, ``AOA Values During the Beginning of the
Flight,'' of Report No. AI 01/19, ``Interim Investigation Report on
Accident to the B737-8 (MAX) Registered ET-AVJ operated by Ethiopian
Airlines on 10 March 2019,'' dated March 9, 2020, of the Federal
Democratic Republic of Ethiopia Ministry of Transport Aircraft
Accident Investigation Bureau.
---------------------------------------------------------------------------
FAA response: FAA regulations do not require the integrated failure
detection capability requested by the commenters, and the 737 MAX air
data system does not include this capability. The FAA has determined
that no change to this AD is necessary because heater failures are
annunciated, and the Unreliable Airspeed NNC provides guidance for
pilots to establish whether there is reliable available data.
4. Comments Regarding Use of Erroneous AOA Sensor Data
Comment summary: A commenter noted that it would be preferable to
suppress the effects of a faulty AOA sensor by declaring it failed and
disregarding it.
FAA response: The unsafe condition identified in this AD is
addressed by the required actions, including installation of the new
FCC software (with the new MCAS) which compares AOA sensor data
supplied to it. The actions required by this AD do not change the
existing 737 MAX air data system, which includes monitoring and
determination of AOA sensor failures, which was certificated without
the capability suggested by the commenter.
5. Comments Regarding Use of STAB OUT OF TRIM Light
Comment summary: Several commenters, including ALPA and the UAE
GCAA, had questions and concerns regarding the STAB OUT OF TRIM light
function and use. The commenters noted the new use of the light to
annunciate FCC failures, and had questions about where the light is
located, when the light would be illuminated, whether pilots would see
it, and whether depressing the RECALL button would be required. Other
commenters were concerned that a light with a dual meaning could lead
to what they referred to as a ``Helios'' type of event, and therefore
there should be a new separate light.
FAA response: On the 737 MAX, there is one STAB OUT OF TRIM light
located on the captain's forward instrument panel above the inboard
display. Per figure 6 to paragraph (h)(7) of this AD, on the ground the
light will illuminate if there is a partial failure of an FCC. In
flight, the light will illuminate if the autopilot does not set the
stabilizer trim correctly. Dispatch is prohibited when the STAB OUT OF
TRIM light is illuminated while on the ground. With electrical power
on, for certain failures of an FCC, the light will be illuminated
continuously, such that no recall action is required of the pilot to
have the light annunciate a fault. The light is in a location that is
visible by both pilots.
The FAA infers that the commenter's reference to Helios is
regarding the Helios Airways Flight 522 accident on August 14, 2005,\7\
related to confusion with a single flight deck warning used for a dual
purpose. On that 737-300 airplane, a single warning served to
annunciate two different, unrelated issues: Takeoff configuration
warning and cabin altitude warning, with two associated distinct
flightcrew procedures. The function of the STAB OUT OF TRIM light
implemented by this AD (it is in the FCC software) is associated with
only one flightcrew procedure (the Stabilizer Out of Trim NNC required
by this AD). Per that procedure, if the light is illuminated on the
ground the flightcrew is directed to not takeoff. Therefore, a new
separate light is not required. No change to this AD is necessary based
on these comments.
---------------------------------------------------------------------------
\7\ Hellenic Republic Ministry of Transport & Communications Air
Accident Investigation & Aviation Safety Board (AAIASB) Helios
Airways Flight HCY522 Aircraft Accident Report, dated November 2006
(https://data.ntsb.gov/Docket/?NTSBNumber=DCA05RA092).
---------------------------------------------------------------------------
6. Comments Regarding Periodic Testing of MCAS
Comment summary: A commenter suggested that MCAS have either an
automatic or a manual self-test that could be tied to the stall warning
system test.
FAA response: Based on the suggestion to tie a self-test to the
stall warning system test, the FAA infers that the commenter is
suggesting that this test be conducted every day. Frequent testing of
MCAS is not required to comply with FAA reliability requirements (14
CFR 25.1309). Even though MCAS is intended only for use during non-
normal flight conditions, the elements of the air data and flight
controls system associated with MCAS are used during every flight and
are continuously monitored. These include AOA sensors and associated
wiring, ADIRUs, databuses, FCCs, and FCC-generated stabilizer trim
commands, such as STS commands or autopilot commands. An existing CMR
(22-CMR-01 in the Boeing MPD) does an operational check of speed trim
and stabilizer trim discrete associated with the FCC computers.
Certification of the new MCAS required implementing a new CMR (22-CMR-
02), which requires periodic testing to verify proper functioning of
the stabilizer trim enable ground path and autopilot arm cutout switch.
In summary, while MCAS is not explicitly tested each flight, any
problem with AOA, ADIRU, FCC, software, etc., will be evidenced
immediately by existing monitors and alerts to be resolved by
maintenance prior to subsequent dispatch, and therefore does not need
to be tested. The FAA has not changed this AD based on this comment.
7. Comments Regarding Maintenance of MCAS
Comment summary: A commenter noted that there is little mention of
[[Page 74572]]
maintenance in the NPRM. Another commenter asked whether dispatch is
prohibited after MCAS failure. Another commenter inquired about
procedures for recording, diagnosing, and repairing the system before
another flight.
FAA response: Design changes mandated via an AD often have new or
revised maintenance documents associated with them.
All of these 737 MAX maintenance-related documents have been
revised:
Boeing 737 Fault Isolation Manual (FIM)
Boeing 737 Aircraft Maintenance Manual (AMM)
Boeing 737 Maintenance Planning Document (MPD)
FAA Maintenance Review Board Report
FAA Master Minimum Equipment List (MMEL) (referenced in
paragraph (i) of this AD)
Collins Aerospace Component Maintenance Manual (CMM) for AOA
Sensor
This AD requires accomplishment of certain Boeing service bulletins
that reference sections of the AMM. Paragraph (i) of this AD requires
actions related to the MMEL. The FAA has released a maintenance Safety
Alert for Operators (SAFO), SAFO 20015, Boeing 737-8 and 737-9
Airplanes: Return to Service,\8\ that identifies related documents.
---------------------------------------------------------------------------
\8\ SAFO 20015 is available at https://www.faa.gov/other_visit/aviation_industry/airline_operators/airline_safety/safo/all_safos/.
---------------------------------------------------------------------------
U.S. airlines must have an approved maintenance program as a
condition of their approval to operate in the U.S. In response to the
comment pertaining to operation after MCAS failure, the MMEL does not
allow dispatch of the airplane with failure of the STS, which includes
MCAS. Maintenance will utilize the FIM and AMM to assess the system,
isolate the fault, resolve the issue, and then return the airplane to
service.
For shop repair of AOA sensors, the Collins Aerospace CMM was
updated to add a final check using different equipment to ensure the
sensor was not mis-calibrated.
For scheduled periodic maintenance, two new tasks are included in
the FAA's Maintenance Review Board Report and in the Boeing MPD. The
first is Item 22-011-00 in the Boeing MPD, which is an operational
check of the MCAS discrete to verify the integrity of MCAS. The other
new task is Item 22-030-00 in the Boeing MPD, which is also a CMR (22-
CMR-02) that operationally checks the stabilizer trim enable ground
path and autopilot arm cutout switch.
Boeing notified 737 MAX operators that these documents were revised
and published via customary communication methods. U.S. part 121 and
part 135 operators must use current CMRs per their OPS SPECS D072
Aircraft Maintenance--Continuous Airworthiness Maintenance Program
(CAMP) Authorization. Continued eligibility for a CAMP authorization
depends on the operator incorporating MPD revisions (which include
CMRs) into their maintenance programs.
8. Comments Regarding Oversight of Maintenance Program
Comment summary: A commenter asked who and what documents and/or
procedure ensures that the maintenance program is enforced.
FAA response: For airplanes registered in the United States,
operators must have an approved maintenance program and must adhere to
it. The FAA oversees U.S. operators. Foreign operators are regulated
and overseen by the civil aviation authority of their country.
9. Comments Regarding Redundancy in the Master Minimum Equipment List
Comment summary: A commenter noted that figure 10 to paragraph (i)
of the proposed AD contained redundant information. The commenter
stated that within figure 10 to paragraph (i) of the proposed AD, both
step (2) and step (8) specify that the autopilot disengage aural
warning system must be operating normally for dispatch. The commenter
added that item 22-10-02 (which is discussed in note 2 to paragraph (i)
of the proposed AD; now note 3 to paragraph (i) of this AD) was deleted
in revision 2 of the MMEL.
FAA response: The FAA agrees that the items mentioned are
redundant. However, this redundancy does not affect compliance with the
AD. In addition, this redundancy will be addressed in the next revision
of the MMEL. No change to this AD is necessary based on this comment.
10. Comments Regarding Inclusion of AOA Sensors in MMEL
Comment summary: A commenter asked if the AOA sensors and MCAS are
in the MEL. The commenter stated that if the AOA and MCAS are
essential, then they must be included in the MEL so that pilots cannot
take off if the AOA sensor or the connection between the AOA and MCAS
is degraded or failed.
FAA response: The FAA infers that the commenter is asking that the
AOA sensors and MCAS be excluded from the MMEL, meaning that the
equipment must be operative for dispatch. On April 10, 2020, the FAA
published the FAA-approved Boeing 737 MAX B-737-8/-9 MMEL, Revision 2,
after public notice and opportunity for comment. The 737 MAX MMEL does
not allow dispatch with the STS (which includes MCAS) inoperative, and
it does not allow dispatch with the position sensing circuit in an AOA
sensor inoperative. The monitoring that would prevent this dispatch
would also detect a failure in the communication between the AOA
sensors and the MCAS function in the FCCs. The MMEL, which includes AOA
sensor heaters, allows for limited dispatch with inoperative AOA
heaters, provided the airplane is not operated in known or forecast
icing conditions. No change to this AD is necessary based on this
comment.
11. Comments Regarding Inclusion of AOA Sensor Heaters in MMEL
Comment summary: The UAE GCAA noted that currently ``AOA heating
system, flight control system, and AP/YD'' are MMEL ``go'' items in
most cases, except for long-range operations and in-icing conditions.
The UAE GCAA noted that it is sometimes difficult for flightcrews to
avoid icing in some flight conditions. The UAE GCAA asked that the FAA
and Boeing make these items ``no go'' in the MMEL.
FAA response: As previously noted, the FAA approved revisions to
the MMEL that removed provisions for dispatch related to MCAS failures.
The MMEL continues to include provisions for limited dispatch for other
unrelated degradation of the flight control system, the autopilot, and
yaw damper. Regarding the AOA heating system, no changes are required
for MMEL item 30-31-02. The MMEL currently states that the AOA sensor
heaters may be inoperative, provided the aircraft is not operated in
known or forecast icing conditions. However, if icing conditions are
encountered, the potential effects due to unheated vanes, including to
air data and to MCAS, do not rise to a hazardous level.
12. Comments Regarding Typographical Error in Note 2 to Paragraph (i)
of the Proposed AD
Comment summary: A4A stated that note 2 to paragraph (i) of the
proposed AD incorrectly refers to MMEL item 22-11-06-2B instead of MMEL
item 22-11-06-02B.
FAA response: The FAA concurs and has revised this note, now note 3
to paragraph (i) of this AD, to refer to MMEL item 22-11-06-02B.
[[Page 74573]]
13. Comments Regarding Removal of Note in Item (4) Within Figure 10 to
Paragraph (i) of the Proposed AD
Comment summary: A4A stated that the FAA should correct conflicts
between the NPRM and policies regarding MEL items pertaining to several
aspects of the flight control system (FCS). A4A noted that figure 10 to
paragraph (i) of the proposed AD contains a note under item (4) stating
that both FCCs must be operative to dispatch. A4A explained that there
are several FCC functions that will continue to have MMEL deferral
relief, as specified in figure 10 to paragraph (i) of the proposed AD
and Revision 2 of the MMEL. A4A added that the item (4) statement in
figure 10 to paragraph (i) of the proposed AD (which states that speed
trim function must be operative for dispatch), combined with the
deletion of the Speed Trim deferral allowance from Revision 2 of the
MMEL, provides a clear indication that Speed Trim must operate normally
for dispatch. For these reasons, A4A recommended that the note be
removed.
FAA response: The FAA has removed the note identified in the A4A
comment. The intent of the note was to emphasize that FCC deactivation
is no longer permitted; this deactivation was associated with Speed
Trim Function relief in previous MMEL revisions. This deactivation came
as part of a required maintenance procedure supported by Boeing in the
Dispatch Deviation Guide (DDG). The FAA acknowledges that the note is
unnecessary, and the revised MMEL itself addresses the condition
specified in the note. For these reasons, the FAA has revised this AD
to remove the note that was under item (4) in figure 10 to paragraph
(i) of the proposed AD.
H. Suggestions for Crew Reporting and Crew Procedures
1. Comments Regarding Crew Reporting of Irregularities
Comment summary: A commenter stated that a procedure should exist
mandating that every 737 MAX operator inform Boeing, the FAA, and local
authorities when any stall warning activation, airspeed disagree alert,
altitude disagree alert, or AOA disagree alert occurs in normal
operation (excluding test flights or readiness flights).
FAA response: For U.S. operators, 14 CFR 121.563 requires the pilot
in command to ensure all mechanical irregularities occurring during
flight time are entered into the maintenance log of the airplane at the
end of that flight time. 14 CFR 121.533, 121.535, and 121.537 also
place responsibility for operational control with the operator and
require operators to exercise operational control through approved or
accepted procedures that lead to the safe dispatch and operation of a
flight. Operators may also provide additional reporting and/or data
collection such as irregularity reports, Aviation Safety Action Program
reports, flight operational quality assurance data, or ad-hoc data
collection from flight data recorders or from aircraft communicating
and reporting system (ACARS) as part of their operational control
system. 14 CFR 121.703 requires reporting of emergency actions during
flight, such as stick shaker activations. The FAA has not changed this
final rule regarding this issue.
2. Comments Regarding Consistency of 737 MAX and 737 NG AFM Procedures
Comment summary: The BALPA questioned whether applicable procedure
changes from the 737 MAX AFM would be applied to the Boeing 737 NG AFM
to avoid confusion if pilots serve in both the Boeing 737 MAX and the
Boeing 737 NG.
FAA response: The FAA expects Boeing will update the eight non-
normal procedures included in this final rule in the Boeing 737 NG AFM.
The FAA is considering mandating these 737 NG AFM changes by a separate
AD rulemaking action. Additionally, the new special emphasis areas \9\
described in section 9.2 of the 737 FSB Report, also apply to the
Boeing 737 NG. Therefore, pilots serving in mixed fleet operations of
the Boeing 737 MAX and the Boeing 737 NG will have consistent
procedures and training in both airplanes. The FAA has not changed this
final rule regarding this issue.
---------------------------------------------------------------------------
\9\ 737 FSB Report, paragraph 6.11, defines a ``special emphasis
area'' as ``A training requirement unique to the aircraft, based on
a system, procedure, or maneuver, which requires additional
highlighting during training. It may also require additional
training time, specialized FSTD, or training equipment.''
---------------------------------------------------------------------------
3. Comments Regarding Flight Crew Operations Manual Content
Comment summary: The Turkish DGCA commented that a comprehensive
description of the flight director bias out of view needed to be
included ``in FCOM'' (the FAA infers the commenter is referring to a
Flight Crew Operations Manual) to ensure pilots will understand that
manual flight is necessary. Another commenter stated that the ``MAX
system'' (which the FAA infers means MCAS) must be included in the
pilot's manual.
FAA response: The information requested by the commenters is in the
AFM. In addition, the FAA has confirmed that Boeing will include the
information requested by the commenter in the FCOM (which is not
mandated by this AD) after publication of this AD.
I. Comments Related to Pilot Training and the Use of Simulators for
Pilot Training
The FAA received several comments to the NPRM docket related to
pilot training and certification and the qualification and use of
simulators for pilot training. The FAA appreciates this input and,
where appropriate, considered the information in other related actions
(e.g., finalizing the 737 FSB Report). Although the comments are beyond
the scope of this rule, the FAA provides the following responses.
1. Comments Regarding Simulator Training
Comment summary: Several commenters, including Flyers Rights, ALPA,
and the Turkish DGCA, stated that the FAA must require simulator
training for pilots operating the Boeing 737 MAX including training on
specific areas.\10\ Two commenters also recommended that the FAA
address perceived deficiencies in 737 MAX simulators related to
accurate representations of the force required by pilots to turn the
pitch trim wheel manually.
---------------------------------------------------------------------------
\10\ Commenters suggested the following areas be included in
simulator training: Stall recovery, flight displays, what to do if
the AOA disagree light illuminates, maneuvers with the AOA sensor
failed, training that mimics the forces needed by pilots,
intricacies of the manual trim wheel and how to implement two-pilot
intervention, autopilot disconnect and flight director bias out of
view, dependencies between MCAS and the other aircraft systems, and
differences in behavior when MCAS is operational versus when MCAS
has failed. Another commenter also noted that computer-based
training (CBT) should include the AOA disagree warning system and
the instrument panel gauges.
---------------------------------------------------------------------------
FAA response: As noted, this AD does not mandate pilot training.
However, consistent with the results of the JOEB operational evaluation
and in accordance with 14 CFR 121.405(e), the FAA is requiring air
carriers to revise all Boeing 737 MAX training curricula to include the
special training as described in the 737 FSB Report. This special
training includes training on all of the areas identified by the
commenters, including the use of manual stabilizer trim in an FFS. The
FAA has taken steps to verify that, in accordance with 14 CFR 60.11(d),
flight simulation training device (FSTD) sponsors have evaluated the
manual stabilizer trim system for proper control forces and travel on
each
[[Page 74574]]
FAA-qualified Boeing 737 MAX FFS. If the forces do not meet the
specified requirements of 14 CFR part 60, Appendix A, the FSTD sponsor
must not allow use of the FFS to conduct training on the manual
stabilizer trim wheel.
The FAA recommends that commenters review the 737 FSB Report and
SAFO 20014, Boeing 737-8 and 737-9 Airplanes: Pilot Training and Flight
Simulation Training Devices (FSTDs) Updates for more information on air
carrier pilot training requirements for the MAX.\11\
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\11\ The 737 FSB Report is available at https://fsims.faa.gov/PICResults.aspx?mode=Publication&doctype=FSBReports; and SAFO 20014
is available at https://www.faa.gov/other_visit/aviation_industry/airline_operators/airline_safety/safo/all_safos/
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2. Comments Regarding New Pilot Type Rating
Comment summary: Some commenters suggested that the FAA establish a
new type rating for the Boeing 737 MAX because, according to the
commenters, the 737 MAX behaves differently than the Boeing 737 Next
Generation (NG), and differences training is not adequate to address
the changes in the 737 MAX from the previous series. Commenters
suggested that a new type rating would ensure that 737 MAX pilots are
properly trained especially in abnormal and emergency situations. The
UAE GCAA raised concerns regarding a mixed fleet consisting of both the
Boeing 737 MAX and the Boeing 737 NG, suggesting that the FAA needed to
examine the impact of mixed fleet operations on crew training.
FAA response: The FAA establishes type ratings through an
operational evaluation of an aircraft conducted by a Flight
Standardization Board. The same process determines the differences
training required for a variation of the aircraft type (e.g., a new
series). For each new series of Boeing Model 737 airplanes, the FAA
conducted the described evaluation and determined that the same pilot
type rating applies to all Boeing Model 737 airplanes. The FAA finds
that this evaluation process has properly determined that the Boeing
737 type rating is appropriate for the 737 MAX. However, in accordance
with 14 CFR 121.400(c)(5), differences training is required for air
carrier pilots to serve on a new series of the Boeing 737. As outlined
in the 737 FSB Report, the differences training from the Boeing 737 NG
to the 737 MAX includes ground and flight training on abnormal and
emergency situations.
Regarding concerns about mixed fleets, the FAA notes that the new
special emphasis areas described in section 9.2 of the 737 FSB Report
also apply to the Boeing 737 NG. Therefore, pilots serving in mixed
fleet operations of the Boeing 737 MAX and the Boeing 737 NG will have
consistent training in both airplanes. The FAA refers commenters to the
737 FSB Report for further information specific to this issue.
3. Comments Regarding Manual Flying Proficiency
Comment summary: Several commenters asserted that pilots have an
over-reliance on automation and need training on manual flying skills
to ensure proficiency.
FAA response: Although these comments are not within the scope of
the proposed rule, the FAA notes that air carrier pilots are required
to demonstrate and maintain proficiency of manual flying skills.\12\
The FAA's commitment to ensuring manual flying proficiency is evident
in its publication of several advisory circulars (ACs) and SAFOs
related to this topic.\13\
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\12\ See 14 CFR 121.423, 121.424, 121.427, 121.441, and part 121
Appendices E and F.
\13\ See AC 120-109A, Stall Prevention and Recovery Training; AC
120-111, Upset Prevention and Recovery Training; AC 120-114, Pilot
Training and Checking (14 CFR part 121, subparts N and O, including
Appendices E and F); SAFO 13002 Manual Flight Operations; and SAFO
17007 Manual Flight Operations Proficiency.
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The FAA continues to emphasize proficiency in manual flying skills
for air carrier pilots by requiring 737 MAX special pilot training that
focuses on manual trim operations, manual flight during MCAS
demonstration at high angles of attack, and manual flight with an
unreliable airspeed condition. The 737 MAX special training is
described in Appendix 7 of the 737 FSB Report.
In September 2019, the FAA presented a working paper at the
International Civil Aviation Organization (ICAO) Assembly seeking the
establishment of a new panel that would address pilot training and
automation dependency. This panel would be an important step in
understanding the scope of automation dependency globally and bring the
international community together to work towards accepted solutions
that could reduce the variability in how the issue is addressed by
individual CAAs.
With broad support for establishing a panel at the Assembly, the
ICAO Air Navigation Commission approved the establishment of a new
Personnel Training and Licensing Panel (PTLP) in June 2020. The U.S.
has been named a member of this panel and the panel's work is
anticipated to begin in early 2021. The FAA will continue to advocate
for taking steps to address automation dependency, manual flight
operations proficiency, and improving pilot management of automated
systems globally. No change to this AD is necessary based on these
comments.
4. Comments Regarding Inclusion of Low-Time Pilots in Operational
Evaluation
Comment summary: The UAE GCAA stated the operational evaluation
should include low-time pilots with a commercial pilot license.
FAA response: As previously described in the ``Related Actions''
section, the FAA completed the operational evaluation jointly with
EASA, ANAC, and TCCA in September 2020. The operational evaluation of
the 737 MAX with the new MCAS included pilots from multiple countries
with varying levels of experience, including a low-time pilot with a
commercial pilot license.
J. Requests for Clarification
Several commenters sought additional information about operation
and behavior of certain systems on the 737 MAX.
1. Comments Regarding Various AOA Thresholds
Comment summary: Several commenters asked questions regarding the
different thresholds used by the new FCC and MDS software when
comparing AOA values. They asserted that use of different thresholds
and different computers should be eliminated. They were concerned that
different thresholds for the two monitors could cause confusion. They
noted that if the difference in AOA values is between the two
thresholds, MCAS would be disabled but the AOA DISAGREE annunciation
would not take place.
FAA response: The FAA provides the following clarification. At
lower speeds (flaps extended), the acceptable difference between the
left and right AOA values is larger. MCAS operates with flaps fully
retracted (higher airspeeds), where the acceptable difference is
smaller.
Airplanes experience significantly different sideslip conditions
during low-speed flight compared to high-speed flight, resulting in
larger differences between left and right sensed AOA values at low
airspeed when compared to high airspeed. It is therefore appropriate
for MCAS, which operates only at high airspeeds (with the flaps
retracted), to have a smaller acceptable
[[Page 74575]]
difference (tighter tolerance) than the AOA DISAGREE alert, which
functions throughout the flight envelope (low and high airspeeds). With
this tighter tolerance, MCAS will be disabled with the smaller
difference between AOA sensor inputs; thus, preventing erroneous MCAS
commands. No change to this AD is necessary based on these comments.
2. Comments Regarding MCAS Activation Prior to Stick Shaker
Comment summary: Several commenters stated that the thresholds for
MCAS activation and for stick shaker activation should ensure that
stick shaker occurs after MCAS activation.
FAA response: The AOA threshold associated with MCAS activation is
less than the AOA threshold associated with stick shaker. Therefore,
MCAS will activate prior to stick shaker.
3. Comments Regarding Function of Column Cutout Switches
Comment summary: Several commenters stated that the NPRM did not
explain the hardware and software modifications that provide new
functionality for control column cutout. They stated that there are
three conditions of control column cutout: Main electric stabilizer
trim column cutout, FCC trim column cutout, and FCC trim software
column cutout. They asked that the FAA explain the significant
modification on the control column cutout as part of this AD.
FAA response: The functionality of the column cutout switches is
described in section 6 of the ``Preliminary Summary of the FAA's Review
of the 737 MAX,'' dated August 3, 2020, which was included in the
docket for this AD at the time of publication of the NPRM. At the base
of the control column are column cutout switches. They inhibit
stabilizer trim commands if the control column moves more than a few
degrees in a direction opposite to the trim command. For example, if
the stabilizer trim command is in the airplane nose-down direction and
the pilot pulls the column aft to raise the nose of the airplane, then
the column cutout switches will inhibit the command to the stabilizer.
There are column cutout switches for commands initiated by the pilot
using the thumb switches on the control wheels, and for commands
initiated by the FCC for autopilot and speed trim commands. The new FCC
software installed as required by paragraph (g) of this AD includes a
redundant software equivalent of the physical switches that interrupt
FCC commands. An FCC will not make a stabilizer command if the column
position is more than a few degrees in the opposite direction of the
pending stabilizer command. The exception occurs when there is an MCAS
airplane nose-down command during high-AOA flight, when the pilot is
typically pulling aft on the control column. During the short duration
of an MCAS activation, the physical and software column cutouts will be
temporarily bypassed to allow the MCAS command.
4. Comments Regarding Term Used in NPRM for Wiring Change
Comment summary: A commenter suggested changing the description of
wiring associated with the horizontal stabilizer trim system. The NPRM
described one of the wires as ``arm'' wiring, and the commenter
suggested that the wiring be referred to as ``power'' wiring.
FAA response: The wiring nomenclature in the NPRM is consistent
with that of the service information required by paragraph (k) of this
AD. No change has been made to this AD based on this comment.
5. Comments Regarding Autopilot Engagement During Stick Shaker
Comment summary: A commenter asked whether the autopilot can be
engaged with the stick shaker active. The commenter noted that flight
data recorder data from the ET302 flight shows that the autopilot was
engaged while the stick shaker was active.
FAA response: Flightcrew training informs pilots how to recover
from a stall, which does not include engagement of the autopilot. In
some cases, the autopilot can be engaged or remain engaged while a
single stick shaker is active. For example, an AOA sensor failure
(e.g., ET302 flight) can cause persistent erroneous stick shaker that
would also affect airspeed and altitude displayed to one of the pilots.
The Airspeed Unreliable procedure required by paragraph (h) of this AD
directs flightcrews to disengage the autopilot, then later allows for
autopilot engagement, but only after a reliable airspeed indication has
been determined. No change has been made to this AD based on this
comment.
6. Comments Regarding Retention of INOP Markers
Comment summary: Several commenters questioned why the FAA proposed
to mandate removing ``INOP'' markers as part of paragraph (j) of the
proposed AD. They suggested that the INOP markers be retained as a
backup or to draw the attention of the flightcrew.
FAA response: The INOP markers are simply stickers that are
covering one of the selectable positions of a dial on the electronic
flight instrument system (EFIS) panel. After installation of the
software required by paragraph (j) of this AD, a display setting that
had been inoperative will be operative. Removal of the INOP marker will
allow the flightcrew to select and use the now operative display
setting. No change to this AD has been made based on these comments.
7. Comments Regarding Boeing Model 737 STS Failures
Comment summary: Several commenters noted that the STS has been on
Boeing Model 737 airplanes since the Boeing Model 737 Classic
airplanes, implemented with a single FCC in control of the function.
They stated that the STS has always been subject to the failure
conditions that drove MCAS to require a dual FCC solution. They
asserted that the STS has not failed to date, but seems vulnerable to a
future failure. They asked whether there is a plan to address STS on
prior models, or if the unhindered aft column cutout saves those
airplanes from further hazards.
FAA response: These comments do not pertain directly to the unsafe
condition of the Boeing 737 MAX that this AD addresses, and therefore
no change to this AD is required based on these comments. Relevant to
these comments, however, the new FCC software installed on the 737 MAX
includes a cross-FCC monitor that will detect and stop any erroneous
FCC-generated stabilizer commands, including STS/MCAS commands. Earlier
Boeing 737 models (pre-MAX) include full-time column cutout switches,
which effectively protect against an erroneous stabilizer trim command.
The pilot stops, or cuts out, the trim command by moving the control
column to oppose the uncommanded trim input. Because of this design
difference between the 737 MAX and earlier versions of the Boeing Model
737, the FAA is not aware of any need to change earlier Boeing 737
models in this respect.
K. Changed Product Rule/Regulations Allowance
This section addresses comments regarding how the FAA certificates
new and derivative aircraft, the overall configuration of the 737 MAX,
whether it is appropriate to include systems like MCAS on airplanes,
and specific comments suggesting changes to crew alerting and
indication on the 737 MAX.
[[Page 74576]]
1. Comments Regarding Certification of Derivative Airplane Models
Comment summary: Several commenters, including the Families of
Ethiopian Airlines Flight 302 and NATCA, did not consider it
appropriate that FAA regulations allowed for 737 MAX airplanes to be
certificated as derivative airplanes of the older, existing Boeing 737
Type Certificate. They highlighted that all Model 737 airplanes are
included on the same type certificate. They stated that FAA regulations
related to this practice should be amended to disallow this. A
commenter suggested that type certificates should expire. Some
commenters contended that FAA regulations allow for existing type
certificates of older designs to be modernized excessively to avoid
complying with new more restrictive requirements. They stated that
every variation needs to be thoroughly reviewed as if it were new. They
also stated that when certifying a derivative aircraft, standard
improvements should be required, such as to include brake temperature
gauges, to make upgrades to the airspeed system, and to introduce
triple redundancy for critical systems. Lastly, they stated that the
737 MAX airplane needs to be recertified with a new type certificate.
Specific to the 737 MAX, they cited the new, larger engines installed
on the old airframe, the age of stabilizer trim system, and the flight
deck caution and warning system.
FAA response: The comments recommend broader reforms to 14 CFR
21.19 and 21.101 and associated guidance that address the criteria and
process used by the FAA, and the other major civil aviation
authorities, when assessing proposed changes to existing products.
These comments do not pertain specifically to correcting the unsafe
condition addressed in this AD. The corrective action mandated by this
AD addresses the identified unsafe condition.
2. Comments Regarding Configuration of 737 MAX
Comment summary: Several commenters, including the Families of
Ethiopian Airlines Flight 302, Flyers Rights, and Aerospace Safety and
Security, Inc., expressed fundamental concerns with the configuration
of the 737 MAX. They stated that the design should be changed, and
should not have been certificated originally. They cited the new,
larger engines installed on the older airplane in a new location that
is forward and higher, and potential associated impacts to
aerodynamics, weight and balance, and pitch-up tendency. Redesign
suggestions include the following: Reverting to using the old engines,
replacing the engines with smaller engines, redesigning the nacelles so
they do not generate lift, and increasing the height of the airplane by
extending the landing gear.
FAA response: The FAA does not prescribe particular designs, but
rather assesses the regulatory compliance and safety of designs
proposed by an applicant. In this case, the FAA certificated the
configuration of the MAX with its current configuration of wing,
engine, landing gear, nacelles, etc., with MCAS as part of the design.
Since the initial certification of the MAX, an unsafe condition was
identified and is addressed by the actions mandated by this AD. The FAA
has determined that the resultant configuration, which includes the new
MCAS, is compliant with the 14 CFR part 25 regulatory requirements and
is safe.
3. Comments Regarding Inclusion of MCAS
Comment summary: Several commenters, including the Families of
Ethiopian Airlines Flight 302, stated that MCAS should not be retained
on the airplane. Some asserted that FAA regulations do not (or, if they
do, they should not) allow for inclusion of a stability augmentation
system like MCAS on an airplane. They stated the airplane should be
redesigned via an aerodynamic configuration change, as discussed
previously, such that it is stable without MCAS, instead of relying on
automation like MCAS to make it stable. They stated that if MCAS is
installed, it would be unacceptable for the airplane to become unstable
with MCAS inoperative. They questioned how much divergent pitch
instability is permitted in commercial aircraft. They stated MCAS
should be replaced with an elevator system solution to resolve a column
force issue.
FAA response: The FAA does not have a factual basis to mandate
removing MCAS from the airplane and finds that the unsafe condition is
appropriately addressed by the requirements of this AD. In addition,
FAA regulations 14 CFR 25.21, 25.671, and 25.672 provide for inclusion
of stability augmentation systems in showing compliance to those
standards. Stability augmentation systems are common features included
in the design of modern transport category airplanes. Subpart B of 14
CFR part 25 requires transport airplanes to have stable pitch
characteristics. The 737 MAX airplane is stable both with and without
MCAS operating. This has been demonstrated on the MAX during FAA flight
testing. Regarding the suggestion to revise the elevator system, the
FAA does not prescribe design, but rather assesses proposed designs,
and the FAA finds the new MCAS meets FAA safety standards.
4. Comments Regarding Crew Alerting System
Comment summary: The Families of Ethiopian Airlines Flight 302
suggested simplifying the Crew Alert System on the 737 MAX so that
flightcrews are not overwhelmed by multiple warning systems. They
asserted that due to provisions of 14 CFR 21.101, the 737 MAX does not
fully comply with 14 CFR 25.1322 concerning flightcrew alerts. They
asserted that an FAA rule (14 CFR 21.101) allows for determining that
it would be ``impractical'' to comply with later amendments of
regulations because the anticipated safety benefits do not justify the
costs necessary to comply with later amendments. They asserted that the
Boeing 737 MAX does not fully comply with 14 CFR 25.1322(b)(3), which
requires advisory alerts ``for conditions that require flightcrew
awareness and may require subsequent flightcrew response''; 14 CFR
25.1322(c)(2), which mandates that warning and caution alerts ``must
provide timely attention-getting cues through at least two different
senses by a combination of aural, visual, or tactile indications''; and
14 CFR 25.1322(d), which states that ``the alert function must be
designed to minimize the effects of false and nuisance alerts.''
Separately, NATCA recommended that all changes to the 737 MAX
comply with the flightcrew alerting requirements in 14 CFR 25.1302
amendment 25-137 and 25.1322 amendment 25-131. Specifically, NATCA
contended that the exception to 14 CFR 25.1322(b)(2), (b)(3), (c)(2),
(d)(1), and (d)(2) granted by the FAA for the 737 MAX should not be
granted for the cockpit changes that would be implemented by the
proposed AD.
Finally, another commenter suggested conducting a holistic
evaluation of flight deck human factors and crew alerting, at least
ensuring all alerts comply with regulations, and reevaluate the
exception to the crew alerting regulation, and to ideally require
installation of an engine indication and crew alerting system (EICAS)
on the 737 MAX.
FAA response: The 737 MAX complies with 14 CFR 25.1322, as
specified in that airplane's certification basis. The 737 MAX crew
alerting system is not substantially changed
[[Page 74577]]
from the 737 NG crew alerting system, which has been shown through
service history to be reliable and safe. The FAA has determined the
existing certification basis for the 737 MAX airplane is appropriate
for the design changes necessary to correct the identified unsafe
condition.
The FAA lacks a factual basis to require any changes (simplifying
the crew alerting system or converting to EICAS) other than those
proposed in the NPRM and mandated by this AD. The unsafe condition
associated with this AD is related to MCAS and how it contributed to
pilot workload. The changes mandated by this AD effectively address the
unsafe condition.
This AD includes two changes related to the crew alerting system.
First, the MDS software change required by paragraph (j) of this AD
implements the AOA DISAGREE alert that was certificated, but
erroneously not implemented, during the initial certification of the
737 MAX. The other change is implemented by the new FCC software
required by paragraph (g) of this AD, which changes the conditions for
which the existing SPEED TRIM FAIL and STAB OUT OF TRIM lights are
illuminated. No change to this AD is necessary based on these comments.
5. Comments Regarding Autothrottle Indication
Comment summary: NATCA asked the FAA to require design changes to
the autothrottle indication to meet current certification regulations,
which are 14 CFR 25.1329(k) at amendment 25-119 and 25.1322.
NATCA stated that the Autothrottle Disconnect alert on the 737 MAX
is a red flashing light with no aural component, which does not meet
the standard alert definitions in 14 CFR 25.1322 and 25.1329(k).
FAA response: This request is unrelated to the unsafe condition
addressed by this AD. There are no changes to the autothrottle
associated with this AD.
L. Certification Process
1. Comments Regarding Compliance and Certification Rigor of MCAS
Comment summary: Some commenters had several questions regarding
the certification associated with the new MCAS, including the basis for
assessing the change, whether the change complies with applicable
regulatory requirements, and the rigor associated with the
certification effort. The commenters questioned the aviation standards
that the FAA used to certify MCAS, including whether the certification
basis is the latest (as commenters believe it should be), whether MCAS
complies, and whether MCAS would comply if it were installed as part of
a new airplane. The comments were associated with hazard
classifications of the software and of certain failures of MCAS, Speed
Trim, and the pitch trim systems. The commenters asserted that a
single-channel system cannot be upgraded to a dual-channel system via a
software change only, and that a hardware change must also be required.
Another commenter asked whether certification testing was done with
MCAS failed. Other commenters suggested specific flight test scenarios.
FAA response: The initial 737 MAX certification and the recent
certification of changes to the 737 MAX used the 737 MAX certification
basis as documented in the Type Certificate Data Sheet. In some areas,
the regulations in the certification basis are at earlier amendment
levels, as allowed by 14 CFR 21.101. The new MCAS complies with those
design standards, and addresses the unsafe condition identified in this
AD. While certifying the new MCAS, the FAA determined the hazard levels
associated with potential failure scenarios after thorough review,
including failure scenarios assessed by FAA pilots.
The new MCAS software was certified as Level A using Radio
Technical Commission for Aeronautics, Inc. (RTCA) DO-178 ``Software
Considerations in Airborne Systems and Equipment Certification'' as a
means of compliance, per Advisory Circular 20-115. Regarding the
assertion that the new MCAS software is insufficient and that a
hardware change is needed, the existing hardware on the 737 MAX
airplane includes two AOA sensors and two FCCs; therefore, with only a
software change to the existing dual-FCC and dual-AOA hardware
configuration, MCAS became a dual-channel system. In addition to the
dual architecture, the new FCC software that implements MCAS includes
integrity monitoring and cross-FCC monitoring. The flight test program
included flights with MCAS failures, and the FAA determined the set of
test scenarios to be sufficient for demonstrating compliance with
applicable 14 CFR part 25 regulations.
2. Comments Regarding Embedding Pilots in Certification Process
Comment summary: Several commenters, including BALPA, suggested
that pilots should be embedded in the certification process and that
average airline pilots should be considered. BALPA stated that the MAX
accidents were due to modifying aircraft with a commonality of design
that precluded the need for a level of certification rigor that the
modification deserved. BALPA cited the Kegworth accident with B737
Engine Instrument System (EIS) change that did not necessitate a new
type rating for EIS-equipped models. BALPA asserted that had line
pilots been involved in certification of that EIS and assessing its
efficiency in imparting information to the pilots, then a different
outcome may have occurred.
FAA's response: The FAA confirms that operational pilots were an
integral part of the certification of the 737 MAX. Several types of
pilots were embedded in the certification process. The FAA has flight
test pilots from its Aircraft Certification Service and aviation safety
inspector pilots from the Flight Standards Service participate in
various parts of the certification process. Additionally, the
certification process involves a cooperative effort from not just the
FAA, but also the aircraft manufacturers, who closely consult with
their customers. The 737 MAX procedures and training were evaluated by
the FAA, EASA, ANAC, and TCCA, including evaluations by pilots from
foreign CAAs and airline pilots from many different countries
representing a wide range of experience. Associated with the actions
required by this AD, 737 MAX flightcrew procedures and training have
been updated and evaluated by the FSB to ensure flightcrews are
provided information about MCAS and that flightcrews will be trained on
the new system before operating the 737 MAX.
3. Comments Regarding Assessment of Flightcrew Response Times
Comment summary: The FAA received two comments, including one from
the Families of Ethiopian Airlines Flight 302, expressing concern
regarding what they described as unrealistic expectations for pilot
response times after failures. The commenters noted that the flightcrew
is a key part of the aircraft control system, and pilot reaction and
response used for certification must be operationally representative
and scientifically validated. A commenter stated that Boeing failed to
examine sufficiently the hazard of repeated MCAS activation due to
erroneously high AOA and failed to consider properly the real-world
pilot reaction to flight deck effects during these potential failures.
FAA response: The FAA agrees that pilot reaction and response used
for certification should be operationally
[[Page 74578]]
representative and validated. The FAA utilized the findings and
recommendations from the accident reports and auditing entities to
drive a closer evaluation of airmanship and pilot response. This
resulted in extensive FAA design reviews and validations conducted in
engineering simulators and in-flight tests. With the original MCAS
design, pilots had full control authority over MCAS, but had to use the
electric stabilizer trim switches, and could disable the system using
the stabilizer trim cutout switches. The new MCAS design eliminates the
need for time-critical pilot actions beyond normal pitch attitude
control using the column alone for any foreseeable failures. The FAA
evaluated possible failures, including AOA failures, during all phases
of flight under the most critical (i.e., takeoff and go-around) phases
of flight and conditions. All associated flight deck effects were
replicated, and the workload and effect of each in combination was
considered and validated. These evaluations were conducted using a wide
range of FAA test pilots, FAA operations pilots, training pilots, and
domestic and international pilots of varying experience. The
evaluations were monitored by human factors specialists to validate
pilot reactions to possible failures of the new design.
The changes to the 737 MAX required by this AD address the unsafe
condition. Therefore, the FAA has not changed this final rule based on
these comments.
4. Comments Regarding Integrated Review Including MCAS
Comment summary: Flyers Rights commented that MCAS should be
evaluated from an integrated whole-aircraft system perspective, and
evaluated with the appropriate catastrophic failure designation.
FAA response: The FAA evaluated MCAS from an integrated whole-
aircraft system perspective. During certification of the new MCAS,
Boeing developed and the FAA approved an integrated SSA that assessed
systems that interface with MCAS. The FAA also approved an analysis of
single and multiple failures, which considered comprehensive impacts of
single and multiple failures. The FAA concluded that for certification
of the new MCAS, Boeing applied the appropriate hazard category
designations.
M. Proposed AD Revisions and Data Requests
1. Comments Regarding Clarification of the Unsafe Condition
Comment summary: A commenter suggested the FAA clarify that the
agency's intent is to address the following unsafe condition:
``Failures that results in repeated nose-down trim commands of the
horizontal stabilizer, that if not addressed, could cause the
flightcrew to have difficulty controlling the airplane, and lead to
excessive nose-down attitude, significant altitude loss, and possible
impact with terrain.''
FAA response: The FAA's description of the unsafe condition in this
AD is accurate. The commenter's proposed description of the unsafe
condition is specific to the narrow accident scenarios. However, the
unsafe conditions and corrective actions addressed by this AD encompass
not only those scenarios described by the commenter, but also other
related scenarios, to ensure they do not occur in service.
2. Comments Requesting Additional Information
Comment summary: The FAA received a variety of requests for
additional information from numerous commenters, including the Families
of Ethiopian Airlines Flight 302 and the Turkish DGCA. These requests
ranged from general to specific. The most broadly-worded included
requests for ``all'' data used by the agency to make its findings and
to propose this rule, and for ``technical details of the proposed
fixes.'' Slightly more tailored requests asked for all data that showed
the airplane's stall characteristics were safe. Very specific requests
also were made, such as for the MCAS SSA including its fault trees and
failure modes and effects analyses (FMEAs), a full description of
system input signals and functions, and details of the in-depth reviews
that a commenter stated took place to establish the acceptability of
implementing MCAS through tailplane movement. Another commenter asked
for internal objections by FAA employees to the NPRM.
FAA response: In reviewing whether a particular issue is an unsafe
condition that requires corrective action, the FAA relies upon data
provided by the manufacturer, including the manufacturer's contractors
and suppliers, which they have designated as proprietary.
The records submitted by the manufacturer to show compliance with
FAA regulations consist of highly technical data and proprietary
compliance methods that the manufacturer developed specific to the 737
MAX design changes. The Trade Secrets Act (TSA) prohibits the FAA and
its employees from disclosing companies' proprietary information. 18
U.S.C. 1905. The information is likewise protected from disclosure
under Freedom of Information Act (FOIA) Exemption 4, and would not be
available to members of the public through a FOIA request for public
access. 5 U.S.C. 552(b)(4).
The FAA supports the public's rights to be reasonably informed of
the basis for agency rulemaking. This does not, however, require
putting interested members of the public in a position to reconstruct
for themselves the underlying technical analyses that are based on
proprietary data; rather, the FAA has provided, as the law specifies,
``either the terms or substance of the proposed rule or a description
of the subjects and issues involved.'' 5 U.S.C. 553. If the FAA were to
disclose or force the disclosure of manufacturers' proprietary data,
there is risk of a chilling effect that would make U.S. aviation less
safe. Manufacturers could become hesitant to provide the FAA with
fulsome design and manufacturing information that best supports the FAA
in addressing potential unsafe conditions, instead seeking to provide
only a bare minimum of information required by 14 CFR 21.3 and 121.703.
FAA analysts would have difficulty obtaining needed technical data, or
such details could be slow in forthcoming during what are sometimes
very urgent analyses.
This particular NPRM was accompanied by the service bulletins for
all of the design changes except for one, and a nearly 100-page summary
of technical information in the ``Preliminary Summary of the FAA's
Review of the Boeing 737 MAX,'' dated August 3, 2020. This information
fairly apprised the public of the issues under consideration in this
rulemaking and enabled informed responses, as evidenced by the more
than two hundred submitted comments, many of which were highly
technical.
For example, the FAA received thirty comments regarding the
adequacy of two AOA sensors on the 737 MAX, with many suggesting that
three sensors are necessary to address the unsafe condition. Some of
these commenters provided detailed engineering rationale, which was
possible based on generally available knowledge of how AOA sensors
work; their reliability; and general principles on system design,
system architecture, and system safety analysis techniques. The
information
[[Page 74579]]
that the FAA supplied thus enabled the public to provide thoughtful
comments on the agency's proposal. As another example, regarding the
new FCC software, the NPRM provided a detailed explanation of how the
new MCAS functions (as implemented by the new FCC software), and how
the FAA proposed that those functions would address the unsafe
condition. Also, in the ``Preliminary Summary of the FAA's Review of
the Boeing 737 MAX,'' dated August 3, 2020, the FAA explained the
safety standards that the agency applied to the software, and how the
agency validated that the new software would function as intended.
Without the need for underlying detail such as the actual MCAS software
code, which could not be interpreted unless it is installed in the
airplane or simulator, the information that the FAA supplied enabled
meaningful comments on the software's functions and how those functions
address the unsafe condition.
Regarding the request for internal objections by FAA employees to
the NPRM, this final rule represents the considered position of the FAA
based on the totality of the agency's work.
3. Comments Regarding Inclusion of Wiring Change in Proposed AD
Comment summary: Several commenters noted that the proposed AD
would mandate wiring separation; however, it was not clear to the
commenters how separating wiring prevents the repeated nose-down trim
commands that this AD is intended to correct. The Boeing service
information indicates that a short circuit between the ``Arm,'' one of
the Control signal lines, and a 28 VDC source will cause a stabilizer
trim runaway. A commenter noted that a continuous trim runaway command
is a different scenario from repeated nose-down trim commands, and
stated that continuous trim runaway should be addressed via an AFM
procedure. While the commenter agreed that future production aircraft
should incorporate this corrective action, the commenter did not find
that an AD mandating corrective action was warranted.
FAA Response: As noted in the NPRM, Boeing re-assessed the
stabilizer trim control system and identified areas of non-compliance
with applicable regulations. The Boeing system safety analysis for the
stabilizer trim control system assessed compliance of the revised
system (with wires separated). Boeing and the FAA determined that wire
separation is needed on the Boeing Model 737 MAX to bring the airplanes
into compliance with the FAA's wire separation safety standards (14 CFR
25.1707).
Regarding the commenter's statement about continuous trim runaway,
the Runaway Stabilizer NNC required by figure 3 to paragraph (h)(4) of
this AD is the AFM procedure to be used ``[i]f uncommanded stabilizer
movement occurs continuously or in a manner not appropriate for flight
conditions.''
4. Comments Regarding Operational Readiness Flight
Comment summary: Several commenters, including Air China, Ameco,
and the UAE GCAA, had questions about the operational readiness flight
required by paragraph (m)(1) of this AD. They did not think the
``Operational Readiness Flight'' (ORF) is sufficiently defined in
Boeing Special Attention Service Bulletin 737-00-1028, July 20, 2020.
They suggested that Boeing publish a separate flight test document for
the 737 MAX ORF rather than the profile in the service bulletin. They
asked whether an AMOC is required if there is a deviation from the ORF
requirements in this AD. They asked whether a subsequent ORF is
required if a fault is identified during the ORF required by this AD.
FAA response: The requirements of the ORF are intentionally brief
and concise and are specified in the service bulletin. The requirements
are to achieve flaps-up flight at or above 20,000 feet above mean sea
level (MSL). If a flight achieves these two criteria, the ORF is
completed. There are no specific test conditions or required maneuvers.
The requirement is written to allow operators the flexibility to
utilize their own typical procedures and flight profiles, provided they
include flight with the flaps up, at or above 20,000 feet above MSL.
The service bulletin includes a suggested flight profile, which an
operator may choose to use. The FAA does not anticipate the need for
AMOCs related to paragraph (m)(1) of this AD due to the brevity of the
requirement.
If a fault is identified during the ORF, a subsequent ORF is not
required by this AD; however, the operator should resolve the
discrepancy using standard procedures, which may require a test flight.
Paragraph (m)(2) of this AD requires resolving any mechanical
irregularities that occurred during the ORF following the operator's
FAA-approved maintenance or inspection program, as applicable.
5. Comments Regarding Necessity for Flight Permit
Comment summary: A4A noted that all Required for Compliance (RC)
steps must be completed ``before further flight'' (including the ORF in
paragraph (m) of the proposed AD) to fully address the NPRM referenced
unsafe condition. A4A asked the FAA to clarify the airworthiness of the
aircraft prior to completing the ORF.
FAA Response: The FAA did not intend the reference to ``before
further flight'' in paragraph (m)(1) of this AD to include the ORF.
Therefore, the FAA has revised paragraph (m)(1) of this AD to require
the ORF to be completed ``before any other flight.'' The FAA finds that
completion of the actions specified in paragraphs (g) through (l) of
this AD is adequate to accomplish the ORF safely. Ferry flights are
permitted prior to or after the ORF as stated in paragraph (n) of this
AD.
6. Comments Regarding Warranty Coverage of Wiring Change Costs
Comment summary: A commenter asserted that the cost of the
horizontal stabilizer wiring change would be borne by the operators,
and suggested that the wiring change should be done at Boeing's
expense.
FAA response: Boeing Service Bulletin 737-27-1318, identified in
the NPRM as the appropriate source of service information for the
horizontal stabilizer wiring change, states that warranty remedies are
available for airplanes in warranty as of March 6, 2020. Although the
NPRM provided all costs, it also noted, ``[a]ccording to the
manufacturer, some or all of the costs of this proposed AD may be
covered under warranty, thereby reducing the cost impact on affected
operators.'' No change to this AD is necessary based on this comment.
7. Comments Regarding Change to AOA Sensor System Test Costs
Comment summary: Based on new data, Boeing clarified and updated
the amount of time it will take to perform the AOA sensor system test:
10 work-hours instead of 40 work-hours. Boeing noted that Boeing
Special Attention Service Bulletin 737-00-1028, dated July 20, 2020
(the source of service information identified in the NPRM for this
test), overstated the time required. Boeing subsequently re-evaluated
the time it takes to do the test and determined the 10-work-hour
estimate better reflects the actual time required to do the AOA sensor
system test. Boeing reported this update in Information Notice IN-737-
00-1028-00-01.
FAA response: The FAA concurs with this requested change to the
work-hour estimate for the reasons provided by the commenter, and has
updated the ``Costs
[[Page 74580]]
of Compliance'' section in this final rule accordingly.
N. Requests for Clarification of Preamble Statements
Various commenters requested clarification of preamble statements.
1. Comments Regarding Preamble Changes From Boeing
Comment Summary: Request to clarify purpose of AOA sensors:
Regarding the Proposed Design Changes section, Boeing requested that
the FAA change ``[t]he updated FCC software would also compare the
inputs from the two sensors to detect a failed AOA sensor'' to ``[t]he
updated FCC software would also compare the inputs from the two sensors
to detect a disagreement between the AOA sensors.'' Boeing stated that
this comment is intended to add clarity and enhance the completeness of
the information included in the NPRM. The software compares two AOA
inputs to determine if they agree, within an appropriate range, and if
the STS should be in an operative state.
Comment Summary: Request to clarify conditions for multiple MCAS
activations: Regarding the Proposed Design Changes section, Boeing
requested that the FAA change ``[a] subsequent activation of MCAS would
be possible only after the airplane returns to a low AOA state, below
the threshold that would cause MCAS activation'' to ``[a] subsequent
activation of MCAS would be possible only after the airplane returns to
a low AOA state, below the threshold that would cause MCAS activation,
and then increases above the activation threshold.'' Boeing stated that
this comment is intended to improve clarity and completeness, and that
the proposed language more fully describes the conditions under which
multiple MCAS activations could occur. The airplane must return to a
low AOA state, below the threshold that would cause MCAS activation,
and then increase above the activation threshold.
Comment Summary: Request to clarify purpose of AOA DISAGREE alert:
Regarding the Proposed Design Changes section, Boeing requested that
the FAA change ``[w]hile the lack of an AOA DISAGREE alert is not an
unsafe condition itself, the FAA is proposing to mandate this software
update to restore compliance with 14 CFR 25.1301 and because the
flightcrew procedures mandated by this AD now rely on this alert to
guide flightcrew action'' to ``[w]hile the lack of an AOA DISAGREE
alert is not an unsafe condition itself, the FAA is proposing to
mandate this software update to restore compliance with 14 CFR 25.1301
and because the flightcrew procedures mandated by this AD now reference
the presence of this alert.'' Boeing stated that this comment is
included to add clarity and avoid confusion. The AOA DISAGREE alert is
not relied upon to guide flightcrew action; it is one of several flight
deck indications that may alert the flightcrew of an unreliable
airspeed event. Due to those integrated flight deck effects, the
flightcrew should execute the un-annunciated Airspeed Unreliable
procedure.
Comment Summary: Request for consistent terminology of non-normal
procedures: Regarding the Proposed Design Changes section, Boeing
requested that the FAA change ``[t]o facilitate the flightcrew's
ability to recognize and respond to undesired horizontal stabilizer
movement and the effects of a potential AOA sensor failure, the FAA
proposes to mandate revising and adding certain operating procedures
(checklists) of the AFM used by the flightcrew for the 737 MAX'' to
``[t]o facilitate the flightcrew's ability to recognize and respond to
undesired horizontal stabilizer movement and the effects of a potential
AOA sensor failure, the FAA proposes to mandate revising and adding
certain non-normal procedures (checklists) of the AFM used by the
flightcrew for the 737 MAX.'' Boeing stated that this comment is
intended to clarify and enhance consistency in the way the NPRM refers
to procedures found in the AFM. The referenced procedures are
technically referred to as ``non-normal procedures'' and the NPRM uses
the ``non-normal procedure'' terminology in the subsequent sentences.
This change simply makes the terminology consistent.
Comment Summary: Request to clarify certain Quick Reference
Handbook (QRH) provisions: Regarding footnote 15, in the Background
section, Boeing requested that the FAA change ``[a]ll of the checklists
that the FAA proposes to revise or add to the AFM are already part of
Boeing's QRH, for the 737 MAX (except for the IAS Disagree checklist,
which is new to both the AFM and the QRH)'' to ``[a]ll of the
checklists that the FAA proposes to revise or add to the AFM are
already part of Boeing's Quick Reference Handbook, or QRH, for the 737
MAX.'' Boeing stated that this comment provides clarification. The IAS
DISAGREE non-normal checklist is not new to the QRH.
Comment Summary: Request to clarify revised Runaway Stabilizer
checklist: Regarding the Proposed Design Changes section, Boeing
requested that the FAA change ``[f]inally, the checklist would be
revised to add a reference item to manually trim the horizontal
stabilizer for pitch control, and note that a two-pilot effort may be
used to correct an out-of-trim condition'' to ``[f]inally, the
checklist would be revised to add a reference item to not reengage the
autopilot or autothrottle, note that a two-pilot effort may be used to
correct an out-of-trim condition, and note that reducing airspeeds will
reduce the effort needed to manually trim the horizontal stabilizer for
pitch control.'' Boeing stated that this comment is included to add
clarity and avoid confusion. The existing checklist directs the
flightcrew to manually trim the horizontal stabilizer. The revised
checklist directs the flightcrew to not re-engage the autopilot or
autothrottle and provides enhanced guidance that reducing airspeeds
reduces the effort needed to manually trim.
Comment Summary: Request to clarify conditions for AOA Disagree
procedure: Regarding the Proposed Design Changes section, Boeing
requested that the FAA change ``[t]herefore, this proposed checklist
would be used when there is an indication, such as an AOA DISAGREE
alert, that the airplane's left and right AOA vanes disagree'' to
``[t]herefore, this proposed checklist would be used when there is an
AOA DISAGREE alert, which indicates that the airplane's left and right
AOA vanes disagree.'' Boeing stated that this comment is included to
add clarity and avoid confusion. The current wording may be interpreted
to suggest that there are multiple reasons to use the AOA Disagree non-
normal procedure. However, the only reason the flightcrew would perform
the AOA Disagree procedure is if the AOA DISAGREE alert is annunciated.
Comment Summary: Request to clarify conditions for certain
checklist steps: Regarding the Proposed Design Changes section, Boeing
requested that the FAA change ``[t]he checklist would also provide
additional steps for the flightcrew to subsequently complete for the
descent, approach, and landing phases of flight'' to ``[i]f IAS
DISAGREE is not shown, the checklist would also provide additional
steps for the flightcrew to subsequently complete the descent,
approach, and landing phases of flight.'' Boeing stated that this
comment is intended to improve clarity. The steps indicated are only
executed by the crew if IAS DISAGREE is not present.
FAA response: The FAA agrees with the foregoing assertions and
Boeing's rationale for its proposed changes. However, because the
proposed changes
[[Page 74581]]
would not affect any requirement of this AD, no change to this AD is
necessary based on this comment.
2. Comments Regarding Credit for MEL Provisions
Comment summary: Air China and Ameco requested that the FAA revise
paragraph (i) of the proposed AD to state that the incorporation of FAA
737 MAX MMEL Revision 2, dated April 10, 2020, into the operator's
existing MEL would show compliance with the requirements of paragraph
(i) of the proposed AD. The commenter also recommended revising
paragraph (o) of the proposed AD to provide credit for the actions
specified in paragraph (i) of the proposed AD, if Revision 2 of the
MMEL was incorporated into the operator's existing MEL before the
effective date of the AD.
FAA response: Since operators are not required to have an MEL, the
FAA cannot revise paragraph (i) of this AD to directly require
operators to incorporate Revision 2 of the MMEL. Paragraph (i) requires
that an operator update their MEL if they want to use it. The FAA
agrees with the intent of the request for credit for incorporating
Revision 2 of the MMEL before the effective date of this AD. Paragraph
(f) of this AD requires that operators ``comply with this AD . . .
unless already done.'' Therefore, in light of that provision, no change
to this AD is necessary regarding these requests.
3. Comments Regarding Service Information: Boeing Special Attention
Service Bulletin 737-27-1318
Comment summary: Air China, Ameco, Boeing, A4A, and the Ethiopian
Airlines Group requested that paragraph (k) of the proposed AD refer to
revised service information for the horizontal stabilizer trim wire
bundle routing change. (The NPRM referred to Boeing Special Attention
Service Bulletin 737-27-1318, Revision 1, dated June 24, 2020, as the
appropriate source of service information for this action, and provided
credit for Boeing Special Attention Service Bulletin 737-27-1318, dated
June 10, 2020.)
The commenters requested credit for the prior accomplishment of
previous revisions of this service information, if certain Installation
Deviation Records (IDRs) identified in Boeing MOM-MOM-20-0608-01B(R3),
dated November 3, 2020, have been incorporated. Boeing stated that the
FAA and Boeing reviewed the IDRs that were issued to operators and
maintenance repair organizations that completed the actions specified
in Revision 1 of the service information, and determined that certain
IDRs addressed installation issues identified in Revision 1 of the
service information that needed to be addressed to ensure proper
incorporation of the changes.
A4A requested that the FAA also allow later FAA-approved revisions
of this service information.
FAA response: Boeing Special Attention Service Bulletin 737-27-
1318, Revision 2, dated November 10, 2020, was issued primarily to
identify the IDRs that were issued to ensure proper incorporation of
changes that were made in accordance with Revision 1 of the service
information. As previously explained in the ``Differences from the
NPRM'' section, the FAA is requiring Revision 2 for the actions
required by paragraph (k) of this AD. The FAA further agrees to provide
credit for the original and Revision 1 of this service information,
provided the referenced 14 IDRs have been incorporated. The FAA also
finds that incorporation of certain FAA-approved Boeing IDRs is
acceptable in lieu of the corresponding RC step identified in the
service information. The FAA has revised paragraphs (k) and (o)
accordingly in this AD. The IDRs identified in Revision 2 of the
service bulletin include an additional IDR that was not identified in
Boeing Multi-Operator Message MOM-MOM-20-0608-01B(R3), dated November
3, 2020; this AD therefore does not refer to the MOM since it is
incomplete.
Regarding the request to allow use of later-approved service
information, an AD may not refer to any document that does not yet
exist. To allow operators to use later revisions of the referenced
document (issued after publication of the AD), either the FAA must
revise the AD to refer to specific later revisions, or operators or the
manufacturer must request approval to use later revisions as an AMOC
for the AD. The FAA has therefore not changed this AD regarding this
issue.
4. Comments Regarding Service Information: Boeing Special Attention
Service Bulletin 737-31-1860
Comment summary: Boeing requested that the FAA refer to Boeing
Special Attention Service Bulletin 737-31-1860, Revision 1, dated July
2, 2020, for installing/verifying MDS software and removing INOP
markers, as specified in paragraph (j) of the proposed AD. (The
proposed AD referred to Boeing Special Attention Service Bulletin 737-
31-1860, dated June 12, 2020, as the appropriate source of service
information for these actions, and also the source of the applicability
information in paragraph (c) of the proposed AD.) Boeing stated that
allowing use of either version would enhance the completeness of the
service information by providing up-to-date information in Revision 1,
as well as credit for the original issue.
FAA response: The FAA finds that the requested action would enhance
the completeness of the service information, and leaves the effectivity
and required actions unchanged. Therefore the FAA has revised
paragraphs (c), (j), and (o) of this AD accordingly.
5. Comments Regarding Service Information: Boeing Alert Requirements
Bulletin 737-22A1342 RB
Comment summary: Paragraph (g) of the proposed AD would require
installing new FCC OPS software. Although no specific compliance method
was provided, the proposed AD referred to AMM 22-11-33 as a source of
guidance for the service information. Ethiopian Airlines Group reported
that it was notified by Boeing of the release of relevant service
information for this software installation: Service Bulletin 737-
22A1342. Ethiopian requested that the FAA consider this service
information as a method of compliance for the proposed FCC OPS
software.
FAA response: The FAA has reviewed Boeing Alert Requirements
Bulletin 737-22A1342 RB, dated November 17, 2020, and determined that
it is an appropriate source of service information for the FCC OPS
software installation. The FAA has revised paragraph (g) of this AD to
add this service information as a method of compliance.
6. Comments Regarding Effects Contributing to Flightcrew Workload
Comment summary: The NPRM preamble stated that following the Lion
Air Flight 610 accident, data from the flight data recorder indicated
that a single erroneously high-AOA sensor input to the flight control
system while the flaps are retracted can cause repeated airplane nose-
down trim of the horizontal stabilizer and multiple flight deck
effects, including stall warning activation, airspeed disagree alert,
and altitude disagree alert, and ``may affect the flightcrew's ability
to accomplish continued safe flight and landing.'' Boeing commented
that these effects instead should be characterized as ``contributing
factors to crew workload.'' Boeing said that its comment was intended
to provide a more specific description of the way in which stall
warning activation, an airspeed disagree alert, and an altitude
disagree alert may affect the flightcrew. Boeing reported that it has
shown, and the FAA has found, that the effects of stall warning
[[Page 74582]]
activation and airspeed/altitude disagree alerts specifically affect
flightcrew workload, an important factor that can affect continued safe
flight and landing. Boeing added that flightcrew workload has been
considered and accounted for in the development of the software update
and non-normal procedures described in the NPRM.
FAA response: The referenced flight deck effects can contribute to
the flightcrew workload, but the FAA finds that the most adverse flight
deck effect in the Lion Air 610 accident was a flight control problem
that affected the flightcrew's ability to accomplish continued safe
flight and landing. Because the proposed changes would not affect any
requirement of this AD, no change to this AD is necessary based on this
comment.
O. Additional Comments Unrelated to the Unsafe Condition
1. Comments Regarding Removal of 737 MAX Airplanes From Service
Comment summary: Multiple commenters requested that the FAA prevent
the 737 MAX from reentering service. Some asked that the FAA do so by
removing the 737 MAX from the Boeing 737 Type Certificate; others
requested that the FAA permanently prohibit the airplane's operation.
The commenters expressed concern for the continued safety of Model
737 MAX airplanes. Some of these commenters expressed concern about a
design that they characterized as old, unsafe, or unstable, with
inferior systems and an undue reliance on electronics and automated
systems. Some commenters questioned the effect on pilot workload of
complex procedures and multiple checklists. Other commenters contended
that the MAX certification process was tainted by a lack of
transparency, reliance on self-certification, a rush to complete
certification, and certification decisions that prioritized profit,
cost reduction, and expedience over safety.
FAA response: The FAA finds that the requirements set forth in this
AD appropriately address the unsafe condition and that upon completion
of the mandated requirements, the 737 MAX airplane meets FAA safety
standards. The FAA acknowledges all of the commenters' safety concerns,
and those concerns align with the FAA's mission of ensuring safety in
air commerce. However, the FAA bases its decisions on data, and because
the corrective actions the FAA is mandating appropriately address the
identified unsafe condition, the FAA lacks a factual basis to mandate
that this airplane be permanently grounded.
2. Comments Regarding Assessment of Other Users of AOA Data
Comment summary: Ethiopian Airlines Group noted that the proposed
AD stated that MCAS logic that was dependent on a single AOA sensor
input will be changed to using two AOA inputs. The commenter asked
about other users of AOA data, either as a single input user or a dual
input user, and whether the FAA can confirm the change to MCAS to use
two AOA inputs does not affect other users requiring only one AOA
input.
FAA response: During the certification of the new MCAS, Boeing and
the FAA scrutinized all users of AOA data and considered normal and
failure conditions. There is no effect on other users of AOA data.
Other users of AOA data are compliant and safe.
3. Comments Not Related to the Unsafe Condition Addressed by This AD
The FAA received a variety of general comments and allegations
related to the competence, ethics, motives, and resources of the
agency, the manufacturer, and their component organizations such as the
organization designation authorization (ODA) and the FAA Boeing
Aviation Safety Oversight Office. These comments came from individuals
and organizations that included the Families of Ethiopian Airlines
Flight 302, Aerospace Safety and Security, Inc., Aerospace Safety
Research Institute, Inc., AFA-CWA, Allied Pilots Association, BALPA,
Ethiopian Airlines Group, and Flyers Rights. These comments are
unrelated to the particular unsafe condition and corrective action, and
therefore are not addressed here.
The FAA also received a variety of comments related to other
potential safety issues on the 737 MAX. The subjects of these comments
include the airplane's susceptibility to high intensity radiated field,
protection of the airplane's rudder cable, the reliability of the
airplane's auto speedbrake system, engine bonding issues, electronic
flight bags, slat track assemblies, the airplane's refueling system,
the auxiliary power unit (APU) fuel tank float switch, the Landing
Attitude Modifier, the airplane's fly-by-wire spoiler system, and the
possibility of foreign object debris. These issues are unrelated to the
particular unsafe condition that this AD addresses and therefore are
not addressed here.
The FAA also received a variety of comments related to proposed
solutions other than those proposed in this rulemaking. These include
limiting the 737 MAX's overwater operation; converting all 737 MAX
airplanes to cargo airplanes; using the Boeing Model 757 instead;
allowing passengers booked on this airplane to change flights;
thoroughly redesigning the airplane's flight control surfaces;
increasing engine power rather than decreasing pitch; limiting airplane
nose up and installing an Alpha floor design used on Airbus airplanes;
requiring certain data to be transmitted from the airplane mid-flight;
requiring certain parameters to be recorded such as the status of
manual electric trim switches; constraining the flight envelope using
control laws or mechanical means; and changing the airplane's
configuration. Some commenters also suggested that the FAA ask the U.S.
Congress to increase the agency's budget and contract out its
functions. These proposed solutions are unrelated to the corrective
actions that were proposed in this rulemaking and therefore will not be
addressed here.
The FAA received a variety of comments and suggestions, including
from the Families of Ethiopian Airlines Flight 302, related to other
airplane models, and requests that the FAA review the safety of those
other airplanes and future airplanes. The FAA is applying lessons
learned on the 737 MAX to current and future FAA certifications and
continued operational safety processes. However, these comments are
unrelated to the unsafe condition addressed by this AD for the 737 MAX,
and therefore will not be addressed here.
The FAA received a variety of comments, including from the Families
of Ethiopian Airlines Flight 302 and the Allied Pilots Association,
related to the adequacy of the regulations that govern how the FAA
processes applications, such as 14 CFR part 21 and 21.101 in
particular, and the design standards in 14 CFR part 25 such as 25.1309
and 25.1322, and how the FAA applies them, such as in AC 21.101 and AC
25.1329. These comments included 13 requests from BALPA for regulatory
and other oversight changes applicable to future aircraft models by the
FAA and other authorities. The FAA's regulatory requirements are
promulgated via notice-and-comment rulemaking as required by the
Administrative Procedure Act (APA), and the public can petition for
rulemaking at https://www.faa.gov/regulations_policies/rulemaking/petition/.
The FAA received several comments, including from the Families of
Ethiopian Airlines Flight 302, to improve its processes and oversight,
such as those for approving proposed
[[Page 74583]]
designs, overseeing manufacturers (including conducting audits),
overseeing the Boeing ODA and other designees including ensuring
freedom from undue pressure, and overseeing all aspects of airline
operations including maintenance practices and repair facilities. The
FAA appreciates and considers all such input; however, it is outside
the scope of this particular rulemaking.
The FAA received requests, including from the Allied Pilots
Association, regarding how the FAA should treat alternative methods of
compliance, known as AMOCs. The FAA acknowledges the commenters'
concern; however, it is premature for the FAA to limit or foreclose the
methods by which an applicant can show compliance with this AD.
The FAA also received requests that the agency create additional
data for public review. These included a request for a comparative
analysis of the difference in stability and control between the subject
airplane and other airplane models. They also included a request for
in-depth reviews to establish the acceptability of implementing MCAS
through tailplane movement. The creation of such additional information
is not necessary to find compliance with FAA regulations, or to find
that the unsafe condition has been addressed.
The FAA also received a request from the Families of Ethiopian
Airlines Flight 302 to commission a new independent review board to
prepare findings.
The FAA commissioned an independent review board, called the
Technical Advisory Board (TAB). The TAB is an independent team of
experts that evaluated the design of the new MCAS. The TAB included FAA
certification specialists and chief scientific and technical advisors
not involved in the original 737 MAX certification program, and subject
matter experts from the U.S. Air Force, the Volpe National
Transportation Systems Center, and the National Aeronautics and Space
Administration. The TAB findings are summarized in the ``Summary of the
FAA's Review of the Boeing 737 MAX,'' which is posted in Docket No.
FAA-2020-0686.
The FAA also received comments that were out of scope for other
reasons, such as doubting the technical ability of the public to
comment on this proposal. Such comments are not being addressed.
Commenters asked how the design changes to correct this unsafe
condition would be distributed to and approved by the CAAs and
implemented by operators worldwide. The FAA, as the airworthiness
authority for the State of Design for these airplanes, is obligated by
ICAO Annex 8 to provide Mandatory Continued Airworthiness Information
to CAAs of other countries.\14\ The FAA will provide the AD to those
authorities, and ICAO Annex 8 requires them to take appropriate action
in response. Therefore, the FAA expects that foreign civil aviation
authorities will adopt similar requirements to those mandated by this
AD, and that foreign operators would then comply with those
requirements.
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\14\ https://www.icao.int/safety/airnavigation/Pages/nationality.aspx.
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Conclusion
The FAA reviewed the relevant data, considered the comments
received, and determined that air safety and the public interest
require adopting this AD with the changes described previously, and
minor editorial changes. The FAA has determined that these minor
changes:
Are consistent with the intent that was proposed in the
NPRM for addressing the unsafe condition; and
Do not add any additional burden upon the public than was
already proposed in the NPRM.
The FAA also determined that these changes will not increase the
economic burden on any operator or increase the scope of this AD.
Related Service Information Under 1 CFR Part 51
The FAA reviewed and approved the following service information.
Boeing Alert Requirements Bulletin 737-22A1342 RB, dated
November 17, 2020, describes procedures for installation of FCC OPS
software on FCC A and FCC B, a software installation verification, and
corrective actions.
Boeing Special Attention Service Bulletin 737-31-1860,
Revision 1, dated July 2, 2020, describes procedures for installation
of MDS software, a software installation verification and corrective
actions, and removal of certain INOP markers on the EFIS control
panels.
Boeing Special Attention Service Bulletin 737-27-1318,
Revision 2, dated November 10, 2020, describes procedures for changing
of the horizontal stabilizer trim wire routing installations.
Boeing Special Attention Service Bulletin 737-00-1028,
dated July 20, 2020, describes procedures for an AOA sensor system test
and an operational readiness flight.
This service information is reasonably available because the
information is posted in the docket and because the interested parties
otherwise have access to it through their normal course of business or
by the means identified in the ADDRESSES section.
Effective Date
Section 553(d) of the APA (5 U.S.C.) generally requires publication
of a rule not less than 30 days before its effective date. However,
section 553(d) authorizes agencies to make rules effective in less than
thirty days, upon a finding of good cause. Due to the relationship
between the Lion Air accident on October 29, 2018, and the Ethiopian
Airlines accident on March 10, 2019, the FAA issued an Emergency Order
of Prohibition on March 13, 2019, generally prohibiting the operation
of 737 MAX airplanes subject to this AD. This AD now identifies the
unsafe condition in the 737 MAX and mandates corrective actions to
correct the unsafe condition so that general operations may resume.
With the publication of this AD, the Emergency Order is no longer
necessary. Accordingly, the FAA is rescinding the Emergency Order
contemporaneously with publication of this final rule. These actions
create the opportunity for operators to safely return the 737 MAX to
service, following a fleet-wide grounding lasting over twenty months.
Therefore, the FAA finds that good cause exists pursuant to 5 U.S.C.
553(d) for making this amendment immediately effective to provide
relief from the grounding restriction as operators take the required
actions to address the unsafe condition.
Costs of Compliance
The FAA estimates that this AD affects 72 airplanes of U.S.
registry. The agency estimates the following costs to comply with this
AD:
[[Page 74584]]
Estimated Costs
----------------------------------------------------------------------------------------------------------------
Cost on U.S.
Action Labor cost Parts cost Cost per product operators
----------------------------------------------------------------------------------------------------------------
FCC OPS installation and 1 work-hour x $85 $0................ $85............... $6,120.
verification. per hour = $85.
AFM revisions................... 1 work-hour x $85 $0................ $85............... $6,120.
per hour = $85.
MDS installation and 1 work-hour x $85 $0................ $85............... $6,120.
verification, INOP marker per hour = $85.
removal.
Stabilizer wiring change........ Up to 79 work- Up to $3,790...... Up to $10,505..... Up to $756,360.
hours x $85 per
hour = Up to
$6,715.
AOA sensor system test.......... 10 work-hours x $0................ $850.............. $61,200.
$85 per hour =
$850.
----------------------------------------------------------------------------------------------------------------
The FAA has received no definitive data that would enable the
agency to provide cost estimates for the operational readiness flight
specified in this AD.
Operators that have a MEL and choose to dispatch an airplane with
an inoperative flight control system affected by this AD would be
required to incorporate certain provisions into the operator's existing
FAA-approved MEL. The FAA has determined that revising the operator's
existing FAA-approved MEL takes an average of 90 work-hours per
operator, although the agency recognizes that this number may vary from
operator to operator. Since operators incorporate MEL changes for their
affected fleet(s), the FAA has determined that a per-operator estimate
is more accurate than a per-airplane estimate. Therefore, the FAA
estimates the average total cost per operator to be $7,650 (90 work-
hours x $85 per work-hour).
According to the manufacturer, some or all of the costs of this AD
may be covered under warranty, thereby reducing the cost impact on
affected operators.
Authority for This Rulemaking
Title 49 of the United States Code specifies the FAA's authority to
issue rules on aviation safety. Subtitle I, Section 106, describes the
authority of the FAA Administrator. Subtitle VII, Aviation Programs,
describes in more detail the scope of the Agency's authority.
The FAA is issuing this rulemaking under the authority described in
Subtitle VII, Part A, Subpart III, Section 44701, General requirements.
Under that section, Congress charges the FAA with promoting safe flight
of civil aircraft in air commerce by prescribing regulations for
practices, methods, and procedures the Administrator finds necessary
for safety in air commerce. This regulation is within the scope of that
authority because it addresses an unsafe condition that is likely to
exist or develop on products identified in this rulemaking action.
Regulatory Findings
The FAA has determined that this AD will not have federalism
implications under Executive Order 13132. This AD will not have a
substantial direct effect on the States, on the relationship between
the national government and the States, or on the distribution of power
and responsibilities among the various levels of government.
For the reasons discussed above, I certify that this AD:
(1) Is not a ``significant regulatory action'' under Executive
Order 12866,
(2) Will not affect intrastate aviation in Alaska, and
(3) Will not have a significant economic impact, positive or
negative, on a substantial number of small entities under the criteria
of the Regulatory Flexibility Act.
List of Subjects in 14 CFR Part 39
Air transportation, Aircraft, Aviation safety, Incorporation by
reference, Safety.
Adoption of the Amendment
Accordingly, under the authority delegated to me by the
Administrator, the FAA amends 14 CFR part 39 as follows:
PART 39--AIRWORTHINESS DIRECTIVES
0
1. The authority citation for part 39 continues to read as follows:
Authority: 49 U.S.C. 106(g), 40113, 44701.
Sec. 39.13 [Amended]
0
2. The FAA amends Sec. 39.13 by:
0
a. Removing Airworthiness Directive (AD) 2018-23-51, Amendment 39-19512
(83 FR 62697, December 6, 2018; corrected December 11, 2018 (83 FR
63561)), and
0
b. Adding the following new AD:
2020-24-02 The Boeing Company: Amendment 39-21332; Docket No. FAA-
2020-0686; Product Identifier 2019-NM-035-AD.
(a) Effective Date
This AD is effective November 20, 2020.
(b) Affected ADs
This AD replaces AD 2018-23-51, Amendment 39-19512 (83 FR 62697,
December 6, 2018; corrected December 11, 2018 (83 FR 63561)) (``AD
2018-23-51'').
(c) Applicability
This AD applies to The Boeing Company Model 737-8 and 737-9
airplanes, certificated in any category, as identified in Boeing
Special Attention Service Bulletin 737-31-1860, Revision 1, dated
July 2, 2020.
(d) Subject
Air Transport Association (ATA) of America Code 22, Auto flight;
27, Flight controls; and 31, Indicating/recording systems.
(e) Unsafe Condition
This AD was prompted by the potential for a single erroneously
high angle of attack (AOA) sensor input received by the flight
control system to result in repeated airplane nose-down trim of the
horizontal stabilizer, which, in combination with multiple flight
deck effects, could affect the flightcrew's ability to accomplish
continued safe flight and landing.
(f) Compliance
Comply with this AD within the compliance times specified,
unless already done.
(g) Installation/Verification of Flight Control Computer (FCC)
Operational Program Software (OPS)
Before further flight, install FCC OPS software version P12.1.2,
part number (P/N) 2274-COL-AC2-26, or later-approved software
versions, on FCC A and FCC B, and do a software installation
verification. During the installation verification, if the approved
software part number is not shown as being installed on FCC A and
FCC B, before further flight, do corrective actions until the
approved software part number is installed on FCC A and FCC B.
Later-approved software versions are only those Boeing software
versions that are approved as a replacement for the applicable
software, and are approved as part of the type design by the FAA
after the effective date of this AD. Accomplishment of all
applicable actions identified as ``RC'' (required for compliance)
in, and in accordance with, the Accomplishment Instructions of
Boeing Alert Requirements Bulletin 737-22A1342 RB, dated November
17, 2020, is acceptable for compliance with the requirements of this
paragraph.
[[Page 74585]]
Note 1 to paragraph (g): Guidance for doing the installation
and installation verification of the FCC OPS software can be found
in Boeing 737-7/8/8200/9/10 Aircraft Maintenance Manual (AMM),
Section 22-11-33.
Note 2 to paragraph (g): Guidance for accomplishing the actions
required by paragraph (g) can also be found in Boeing Alert Service
Bulletin 737-22A1342, dated November 17, 2020, which is referred to
in Boeing Alert Requirements Bulletin 737-22A1342 RB, dated November
17, 2020.
(h) Airplane Flight Manual (AFM) Revisions
Before further flight, revise the existing AFM to include the
changes specified in paragraphs (h)(1) through (10) of this AD.
Revising the existing AFM to include the changes specified in
paragraphs (h)(2) through (10) of this AD may be done by inserting a
copy of figure 1 to paragraph (h)(2) through figure 9 to paragraph
(h)(10) into the existing AFM.
(1) In the Certificate Limitations and Operating Procedures
chapters, remove the information identified as ``Required by AD
2018-23-51.''
(2) In the Operating Procedures chapter, revise the General
paragraph to include the information in figure 1 to paragraph (h)(2)
of this AD.
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(3) In the Operating Procedures chapter, replace the existing
Airspeed Unreliable paragraph with the information in figure 2 to
paragraph (h)(3) of this AD.
[[Page 74586]]
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[[Page 74587]]
[GRAPHIC] [TIFF OMITTED] TR20NO20.033
(4) In the Operating Procedures chapter, replace the existing
Runaway Stabilizer paragraph with the information in figure 3 to
paragraph (h)(4) of this AD.
[[Page 74588]]
[GRAPHIC] [TIFF OMITTED] TR20NO20.034
(5) In the Operating Procedures chapter, replace the existing
Stabilizer Trim Inoperative paragraph with the information in figure
4 to paragraph (h)(5) of this AD.
[[Page 74589]]
[GRAPHIC] [TIFF OMITTED] TR20NO20.035
(6) In the Operating Procedures chapter, add the information in
figure 5 to paragraph (h)(6) of this AD.
[GRAPHIC] [TIFF OMITTED] TR20NO20.036
(7) In the Operating Procedures chapter, add the information in
figure 6 to paragraph (h)(7) of this AD.
[[Page 74590]]
[GRAPHIC] [TIFF OMITTED] TR20NO20.037
(8) In the Operating Procedures chapter, add the information in
figure 7 to paragraph (h)(8) of this AD.
[GRAPHIC] [TIFF OMITTED] TR20NO20.038
(9) In the Operating Procedures chapter, add the information in
figure 8 to paragraph (h)(9) of this AD.
[[Page 74591]]
[GRAPHIC] [TIFF OMITTED] TR20NO20.039
(10) In the Operating Procedures chapter, add the information in
figure 9 to paragraph (h)(10) of this AD.
[GRAPHIC] [TIFF OMITTED] TR20NO20.040
(i) Minimum Equipment List (MEL) Provisions for Inoperative Flight
Control System Functions
In the event that the airplane functions associated with the
flight control system as modified by this AD are inoperative, an
airplane may be operated (dispatched) only if the provisions
specified in figure 10 to paragraph (i) of this AD are incorporated
into the operator's existing FAA-approved MEL.
[[Page 74592]]
[GRAPHIC] [TIFF OMITTED] TR20NO20.041
Note 3 to paragraph (i): The MEL provisions specified in figure
10 to paragraph (i) of this AD correspond to Master Minimum
Equipment List (MMEL) items 22-10-01B, 22-10-02, 22-10-03, 22-11-01,
22-11-02, 22-11-05-02B, 22-11-06-02B, 22-11-08-01A, 22-11-08-01B,
22-11-10A, 22-11-10B, and 27-41-01, in the existing FAA-approved
Boeing 737 MAX B-737-8/-9 MMEL, Revision 2, dated April 10, 2020,
which can be found on the Flight Standards Information Management
System (FSIMS) website, https://fsims.faa.gov/PICResults.aspx?mode=Publication&doctype=MMELByModel.
(j) Installation/Verification of MAX Display System (MDS) Software,
Removal of INOP Markers
Before further flight, do all applicable actions identified as
``RC'' in, and in accordance with, the Accomplishment Instructions
of Boeing Special Attention Service Bulletin 737-31-1860, Revision
1, dated July 2, 2020.
(k) Horizontal Stabilizer Trim Wire Bundle Routing Change
Before further flight, do all applicable actions identified as
``RC'' in, and in accordance with, the Accomplishment Instructions
of Boeing Special Attention Service Bulletin 737-27-1318, Revision
2, dated November 10, 2020.
(l) AOA Sensor System Test
Before further flight, do all applicable actions identified as
``RC'' for the ``Angle of Attack (AOA) Sensor System Test''
specified in, and in accordance with, the Accomplishment
Instructions of Boeing Special Attention Service Bulletin 737-00-
1028, dated July 20, 2020.
(m) Operational Readiness Flight
(1) After accomplishment of all applicable required actions in
paragraphs (g) through (l) of this AD, do all applicable actions
identified as ``RC'' for the ``Operational Readiness Flight''
specified in, and in accordance with, the Accomplishment
Instructions of Boeing Special Attention Service Bulletin 737-00-
1028, dated July 20, 2020. The ``Operational Readiness Flight''
required by this paragraph must be accomplished before any other
flight. A special flight permit is not required to accomplish the
``Operational Readiness Flight'' required by this paragraph.
(2) After the ``Operational Readiness Flight'' and before
further flight, any mechanical irregularities that occurred during
the ``Operational Readiness Flight'' must be resolved following the
operator's FAA-approved maintenance or inspection program, as
applicable.
(n) Special Flight Permits
Special flight permits may be issued in accordance with 14 CFR
21.197 and 21.199 to operate the airplane to a location where the
actions of this AD can be performed.
(o) Credit for Previous Actions
(1) This paragraph provides credit for the actions specified in
paragraph (j) of this AD, if those actions were performed before the
effective date of this AD using Boeing Special Attention Service
Bulletin 737-31-1860, dated June 12, 2020.
(2) This paragraph provides credit for the actions specified in
paragraph (k) of this AD, if those actions were performed before the
effective date of this AD using Boeing Special Attention Service
Bulletin 737-27-1318, dated June 10, 2020, or Revision 1, dated June
24, 2020, provided the 14 Installation Deviation Records (IDRs)
identified in paragraph 1.D., ``Description,'' of Boeing Special
Attention Service Bulletin 737-27-1318, Revision 2, dated November
10, 2020, have been incorporated on the airplane. Accomplishment of
FAA-approved Boeing IDRs not identified in paragraph 1.D.,
``Description,'' of Boeing Special Attention Service Bulletin 737-
27-1318, Revision 2, dated November 10, 2020, before the effective
date of this AD, is acceptable for compliance with the corresponding
RC steps specified in Special Attention Service Bulletin 737-27-
1318, Revision 1, dated June 10, 2020, provided those IDRs reference
Boeing Special Attention Service Bulletin 737-27-1318, Revision 1,
dated June 10, 2020.
[[Page 74593]]
(p) Alternative Methods of Compliance (AMOCs)
(1) The Manager, Seattle ACO Branch, FAA, has the authority to
approve AMOCs for this AD, if requested using the procedures found
in 14 CFR 39.19. In accordance with 14 CFR 39.19, send your request
to your principal inspector or responsible Flight Standards Office,
as appropriate. If sending information directly to the manager of
the certification office, send it to the attention of the person
identified in paragraph (q)(1) of this AD. Information may be
emailed to: [email protected].
(2) Before using any approved AMOC, notify your appropriate
principal inspector, or lacking a principal inspector, the manager
of the responsible Flight Standards Office.
(3) AMOCs approved previously for AD 2018-23-51 are not approved
as AMOCs for this AD.
(4) For service information that contains steps that are labeled
as RC, the provisions of paragraphs (p)(4)(i) and (ii) of this AD
apply.
(i) The steps labeled as RC, including substeps under an RC step
and any figures identified in an RC step, must be done to comply
with the AD. If a step or substep is labeled ``RC Exempt,'' then the
RC requirement is removed from that step or substep. An AMOC is
required for any deviations to RC steps, including substeps and
identified figures.
(ii) Steps not labeled as RC may be deviated from using accepted
methods in accordance with the operator's maintenance or inspection
program without obtaining approval of an AMOC, provided the RC
steps, including substeps and identified figures, can still be done
as specified, and the airplane can be put back in an airworthy
condition.
(q) Related Information
(1) For more information about this AD, contact Ian Won,
Manager, Seattle ACO Branch, FAA, 2200 South 216th St., Des Moines,
WA 98198; phone and fax: 206-231-3500; email: [email protected].
(2) Service information identified in this AD that is not
incorporated by reference is available at the addresses specified in
paragraphs (r)(3) and (4) of this AD.
(r) Material Incorporated by Reference
(1) The Director of the Federal Register approved the
incorporation by reference (IBR) of the service information listed
in this paragraph under 5 U.S.C. 552(a) and 1 CFR part 51.
(2) You must use this service information as applicable to do
the actions required by this AD, unless the AD specifies otherwise.
(i) Boeing Alert Requirements Bulletin 737-22A1342 RB, dated
November 17, 2020.
(ii) Boeing Special Attention Service Bulletin 737-00-1028,
dated July 20, 2020.
(iii) Boeing Special Attention Service Bulletin 737-27-1318,
Revision 2, dated November 10, 2020.
(iv) Boeing Special Attention Service Bulletin 737-31-1860,
Revision 1, dated July 2, 2020.
(3) For service information identified in this AD, contact
Boeing Commercial Airplanes, Attention: Contractual & Data Services
(C&DS), 2600 Westminster Blvd., MC 110-SK57, Seal Beach, CA 90740-
5600; telephone 562-797-1717; internet https://www.myboeingfleet.com.
(4) You may view this service information at the FAA,
Airworthiness Products Section, Operational Safety Branch, 2200
South 216th St., Des Moines, WA. For information on the availability
of this material at the FAA, call 206-231-3195.
(5) You may view this service information that is incorporated
by reference at the National Archives and Records Administration
(NARA). For information on the availability of this material at
NARA, email [email protected], or go to: https://www.archives.gov/federal-register/cfr/ibr-locations.html.
Issued on November 18, 2020.
Lance T. Gant,
Director, Compliance & Airworthiness Division, Aircraft Certification
Service.
[FR Doc. 2020-25844 Filed 11-18-20; 4:15 pm]
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