[Federal Register Volume 62, Number 187 (Friday, September 26, 1997)]
[Rules and Regulations]
[Pages 50494-50497]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 97-25509]
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DEPARTMENT OF TRANSPORTATION
Federal Aviation Administration
14 CFR Part 25
[Docket No. NM-141; Special Conditions No. 25-ANM-132]
Special Conditions: Boeing Model 737-600/-700/-800; High
Intensity Radiated Fields (HIRF)/Engine Stoppage
AGENCY: Federal Aviation Administration (FAA), DOT.
ACTION: Final special conditions.
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SUMMARY: These special conditions are issued for Boeing Model 737-600/-
700/-800 airplanes. These airplanes will have novel and unusual design
features when compared to the state of technology envisioned in the
airworthiness standards for transport category airplanes. These special
conditions contain the additional safety standards that the
Administrator considers necessary to establish a level
[[Page 50495]]
of safety equivalent to that provided by the existing airworthiness
standards.
EFFECTIVE DATE: September 17, 1997.
FOR FURTHER INFORMATION CONTACT:
Gregory Dunn, FAA, Standardization Branch, ANM-113, Transport Airplane
Directorate, Aircraft Certification Service, 1601 Lind Avenue SW.,
Renton, Washington, 98055-4056; telephone (425) 227-2799; facsimile
(425) 227-1149.
SUPPLEMENTARY INFORMATION:
Background
On February 4, 1993, Boeing submitted an application for an
amendment to Type Certificate A16WE to include the next generation 737
family of airplanes. Two of these airplanes will have the same length
as the present 737-300 and 737-500. The third version will be the
existing 737-400, stretched to add two additional passenger rows. In
addition, all models will have increased wing size, higher thrust
engines, and body structure modifications due to increased design
weights and higher wing and tail loads. The maximum operating altitude
is to be increased from 37,000 ft. to 41,000 ft. The long range cruise
speed is increased to 0.78 Mach or better. The range is increased to be
transcontinental of approximately 2,950 nmi. There is only one engine
type being offered, which is a derivative of the existing CFM56
referred to as the CFM56-7.
Type Certification Basis
Under the provisions of 14 CFR Sec. 21.101, Boeing must show that
the Model 737-600/-700/-800 airplanes meet the applicable provisions of
the regulations incorporated by reference in Type Certificate A16WE, or
the applicable regulations in effect on the date of application for the
change to the Model 737. The regulations incorporated by reference in
the type certificate are commonly referred to as the ``original type
certification basis.'' The certification basis for the Model 737-600/-
700/-800 airplanes includes 14 CFR part 25, as amended by Amendments
25-1 through 25-77, except as indicated below:
------------------------------------------------------------------------
At amdt.
Section No. Title 25-
------------------------------------------------------------------------
25.365........................ Pressurized Compartment Loads 0
25.561........................ Emergency Landing Conditions-- 0
General.
25.562........................ Emergency Landing Dynamic * 64
Conditions.
25.571........................ Damage-tolerance and Fatigue ** 0,77
Evaluation of Structure.
25.607........................ Fasteners.................... ** 0,77
25.631........................ Bird Strike Damage........... ** 0,77
25.699........................ Lift and Drag Device ** 0,77
Indicator.
25.783(f)..................... Doors........................ ** 15,77
25.807(c)(3).................. Emergency Exits.............. 15
25.813........................ Emergency Exit Access........ 45
25.832........................ Cabin Ozone Concentration.... *** 0,77
25.1309....................... Equipment, Systems and ** 0,77
Installations.
25.1419(c).................... Ice Protection............... ** 23,77
------------------------------------------------------------------------
Boeing has also elected to comply with Amendments 25-78 and 25-80 and
portions of Amendments 25-79, 25-84, and 25-86.
* Flight attendants seats will be qualified to Technical Standard Order
C127. Passenger and flight deck seats will comply with 14 CFR 25.562
(a),(b),((c)(1),(2),(3),(4),(7), and (8)).
** Applicable to new and significantly modified structure and systems
and portions of the airplane affected by these changes. Where two
amendment levels are shown for the same paragraph, the number without
the asterisks (*) applies to structures, systems, and portions of the
airplane which are not new or significantly modified. The structure,
systems, and components which comply with the later amendment will be
identified in Boeing document D010A001, approved by the FAA and JAA,
and referenced on the type certificate data sheet.
*** Boeing provides FAA approved data (Document number D6-49779) to 737
operators to enable the operators to show ozone compliance per 14 CFR
121.578 for their specific route structures.
Amendment level ``0'' is the original published version of Part 25
(February 1, 1965).
In addition, the certification basis will be upgraded to include
the Part 25 complement to any Part 121 amendments adopted prior to the
certification date and having impact on transport category airplane
type designs, and these special conditions.
In addition to the applicable airworthiness regulations and special
conditions, the Model 737-600/-700/-800 airplanes must comply with the
fuel vent and exhaust emission requirements of 14 CFR part 34, and the
noise certification requirements of 14 CFR part 36.
If the Administrator finds that the applicable airworthiness
regulations (i.e., part 25, as amended) do not contain adequate or
appropriate safety standards for the Boeing Model 737-600/-700/-800
airplanes because of novel or unusual design features, special
conditions are prescribed under the provisions of 14 CFR 21.16 to
establish a level of safety equivalent to that established in the
regulations.
Special conditions, as appropriate, are issued in accordance with
14 CFR 11.49 after public notice, as required by 14 CFR 11.28 and
11.29, and become part of the type certification basis in accordance
with 14 CFR 21.101(b)(2).
Special conditions are initially applicable to the model for which
they are issued. Should the type certificate for that model be amended
later to include any other model that incorporates the same novel or
unusual design feature, or should any other model already included on
the same type certificate be modified to incorporate the same novel or
unusual design feature, the special conditions would also apply to the
other model under the provisions of 14 CFR 21.101(a)(1).
Novel or Unusual Design Features
The Boeing Model 737-600/-700/-800 airplanes will incorporate new
avionic/electronic systems, such as the Air Data Inertial Reference
System (ADIRS) and Common Display System (CDS), that perform critical
functions. These systems may be vulnerable to HIRF external to the
airplane. In addition, the CFM56-7B engine proposed for the Boeing 737-
700 airplane is a high-bypass ratio fan jet engine that will not seize
and produce transient torque loads in the same manner that is
envisioned by current Sec. 25.361(b)(1) related to ``sudden engine
stoppage.''
Discussion
There is no specific regulation that addresses protection
requirements for electrical and electronic systems from HIRF. Increased
power levels from ground-based radio transmitters and the growing use
of sensitive electrical and electronic systems to command and control
airplanes have made it necessary to provide adequate protection.
To ensure that a level of safety is achieved equivalent to that
intended by the regulations incorporated by reference, a special
condition is needed for the Boeing Model 737-600/-700/-800, which
requires that new electrical and electronic systems that perform
critical functions be designed and installed to preclude component
damage and interruption of function due to both the direct and indirect
effects of HIRF.
For the CFM56-7B engine, the limit engine torque load imposed by
sudden engine stoppage due to malfunction or structural failure (such
as compressor jamming) has been a specific requirement for transport
category
[[Page 50496]]
airplanes since 1957. The size, configuration, and failure modes of jet
engines has change considerably from those envisioned in 14 CFR
25.361(b) when the engine seizure requirement was first adopted.
Relative to the engine configurations that existed when the rule
was developed in 1957, the present generation of engines are
sufficiently different and novel to justify issuance of a special
condition to establish appropriate design standards.
The FAA is developing a new regulation and new advisory circular
that will provide more comprehensive criteria for treating engine loads
resulting from structural failures. In the meantime, a special
condition is needed to establish appropriate criteria for the Boeing
737-600/-700/-800 airplanes.
High-Intensity Radiated Fields (HIRF)
With the trend toward increased power levels from ground-based
transmitters, plus the advent of space and satellite communications,
coupled with electronic command and control of the airplane, the
immunity of critical digital avionics systems to HIRF must be
established.
It is not possible to precisely define the HIRF to which the
airplane will be exposed in service. There is also uncertainty
concerning the effectiveness of airframe shielding for HIRF.
Furthermore, coupling of electromagnetic energy to cockpit-installed
equipment through the cockpit window apertures is undefined. Based on
surveys and analysis of existing HIRF emitters, an adequate level of
protection exists when compliance with the HIRF protection special
condition is shown with either paragraphs 1, or 2 below:
1. A minimum threat of 100 volts per meter peak electric field
strength from 10 KHz to 18 GHz.
a. The threat must be applied to the system elements and their
associated wiring harnesses without the benefit of airframe shielding.
b. Demonstration of this level of protection is established through
system tests and analysis.
2. A threat external to the airframe of the following field
strengths for the frequency ranges indicated.
------------------------------------------------------------------------
Peak (V/ Average
Frequency M) (V/M)
------------------------------------------------------------------------
10 KHz-100 KHz...................................... 50 50
100 KHz-500 KHz..................................... 60 60
500 KHz-2 MHz....................................... 70 70
2 MHz-30 MHz........................................ 200 200
30 MHz-100 MHz...................................... 30 30
100 MHz-200 MHz..................................... 150 33
200 MHz-400 MHz..................................... 70 70
400 MHz-700 MHz..................................... 4,020 935
700 MHz-1 GHz....................................... 1,700 170
1 GHz-2 GHz......................................... 5,000 990
2 GHz-4 GHz......................................... 6,680 840
4 GHz-6 GHz......................................... 6,850 310
6 GHz-8 GHz......................................... 3,600 670
8 GHz-12 GHz........................................ 3,500 1,270
12 GHz-18 GHz....................................... 3,500 360
18 GHz-40 GHz....................................... 2,100 750
------------------------------------------------------------------------
Limit Engine Torque Loads for Sudden Engine Stoppage
In order to maintain the level of safety envisioned by
Sec. 25.361(b), more comprehensive criteria are needed for the new
generation of high bypass engines. This special condition distinguishes
between the more common events and those rare events resulting from
structural failures in the engine. For these more rare but severe
events, these criteria allow deformation in the engine supporting
structure in order to absorb the higher energy associated with the high
bypass engines, while at the same time protecting the adjacent primary
structure in the wing and fuselage by applying an additional factor on
these loads.
Discussion of Comments
Notice of proposed special conditions No. SC-97-3-NM for the Boeing
737-600/-700/-800 airplanes was published in the Federal Register on
May 14, 1997 (62 FR 26453).
Comments were received from an engine manufacturer who, while
supporting the need for the engine torque loads requirements, offers
the following comments for consideration.
The commenter recommends that the words ``* * * and that could
cause a shutdown due to vibrations'' be removed from paragraph
2(b)(1)(i) of the special conditions. The commenter states that its
position is based on a comparison of the proposed special condition
with similar work currently underway within the Aviation Rulemaking
Advisory Committee (ARAC). The commenter notes differences between
these two proposals. For example, the special condition adds a
provision that the engine malfunction for limit load calculation be
such that it ``could cause a shutdown due to engine vibrations,'' while
this provision was removed from the ARAC proposal, whose intent is to
address engine events beyond maximum acceleration and other than
structural failures, seizures, jamming, and unbalance, such as engine
surge. The commenter further notes that the special condition does not
explicitly state that the limit torque acts simultaneously with 1g
flight loads, although this may be intended.
The FAA recognizes that the ARAC working group is studying this
issue and that its final proposal may be different from what has
already been applied as a special condition on several airplanes.
However, until more definitive criteria have been accepted by industry
and by the FAA, the special condition will remain unchanged. The
special condition is based on the assumption that the airplane will be
subjected to 1g flight loads throughout the engine torque event.
Applicability
As discussed above, these special conditions are applicable to the
Model 737-600/-700/-800 airplanes. Should Boeing Commercial Airplane
Group apply at a later date for a change to the type certificate to
include another model incorporating the same novel or unusual design
feature, the special conditions would apply to that model as well under
the provisions of 14 CFR 21.101(a)(1).
Under standard practice, the effective date of final special
conditions would be 30 days after the date of publication in the
Federal Register; however, as the certification date for the Model 737-
600/-700/-800 airplanes is imminent, the FAA finds that good cause
exists to make these special conditions effective upon issuance.
Conclusion
This action affects only certain design features on the Boeing
Model 737-600/-700/-800 airplanes. It is not a rule of general
applicability and affects only the applicant who applied to the FAA for
approval of these features on the airplane.
List of Subjects in 14 CFR Part 25
Aircraft, Aviation safety, Reporting and recordkeeping
requirements.
The authority citation for these special conditions is as follows:
Authority: 49 U.S.C. 106(g), 40113, 44701, 44702, 44704.
The Special Conditions
Accordingly, pursuant to the authority delegated to me by the
Administrator, the following special conditions are issued as part of
the type certification basis for Boeing Model 737-600/-700/-800
airplanes.
1. Protection from Unwanted Effects of High-Intensity Radiated
Fields (HIRF). Each electrical and electronic system that performs
critical functions must be designed and installed to ensure that the
operation and operational capability of these systems
[[Page 50497]]
to perform critical functions are not adversely affected when the
airplane is exposed to high intensity radiated fields.
For the purpose of this special condition, the following definition
applies:
Critical Functions. Functions whose failure would contribute to or
cause a failure condition that would prevent the continued safe flight
and landing of the airplane.
2. Engine Torque Loads. In lieu of compliance with Sec. 25.361(b),
compliance with the following must be shown:
(b) For turbine engine installations, the mounts and local
supporting structure must be designed to withstand each of the
following:
(1) The maximum torque load, considered as limit, imposed by:
(i) sudden deceleration of the engine due to a malfunction that
could result in a temporary loss of power or thrust capability, and
that could cause a shutdown due to vibrations; and
(ii) the maximum acceleration of the engine.
(2) The maximum torque load, considered as ultimate, imposed by
sudden engine stoppage due to a structural failure, including fan blade
failure.
(3) The load condition defined in paragraph (b)(2) of this section
is also assumed to act on adjacent airframe structure, such as the wing
and fuselage. This load condition is multiplied by a factor of 1.25 to
obtain ultimate loads when the load is applied to the adjacent wing and
fuselage supporting structure.
Issued in Renton, Washington, on September 17, 1997.
Vi L. Lipski,
Acting Manager, Transport Airplane Directorate, Aircraft Certification
Service.
[FR Doc. 97-25509 Filed 9-25-97; 8:45 am]
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