[Federal Register Volume 64, Number 232 (Friday, December 3, 1999)]
[Rules and Regulations]
[Pages 67701-67705]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 99-31396]
[[Page 67701]]
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DEPARTMENT OF TRANSPORTATION
Federal Aviation Administration
14 CFR Part 25
[Docket No. NM162; Special Conditions No. 25-154-SC]
Special Conditions: Bombardier Model DHC-8-400 Airplane;
Automatic Takeoff Thrust Control System
AGENCY: Federal Aviation Administration (FAA), DOT.
ACTION: Final special conditions.
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SUMMARY: These special conditions are issued for the Bombardier Model
DHC-8-400 series airplanes. This new airplane will have a novel or
unusual design feature associated with an Automatic Takeoff Thrust
Control System (ATTCS). The applicable airworthiness regulations do not
contain appropriate safety standards for approach climb performance
using an ATTCS. These special conditions contain the additional safety
standards that the Administrator considers necessary to establish a
level of safety equivalent to that established by the existing
airworthiness standards.
EFFECTIVE DATE: November 22, 1999.
FOR FURTHER INFORMATION CONTACT: Greg Dunn, FAA, Transport Airplane
Directorate, Aircraft Certification Office, Standardization Branch,
ANM-113, 1601 Lind Avenue SW., Renton, Washington, telephone (425) 227-
2799; facsimile (425) 227-1149.
SUPPLEMENTARY INFORMATION:
Background
On January 31, 1995, Bombardier Regional Aircraft, 123 Garratt
Blvd., Downsview, Ontario, Canada, M3K 1Y5, applied for an amended type
certificate to include the new Bombardier Model DHC-8-400 airplane. The
Bombardier Model DHC-8-400, which is a derivative of the Bombardier
(formerly de Havilland, Inc.) Model DHC 8-300 series airplanes
currently under Type Certificate No. A13NM is a medium-sized airplane
powered by two Pratt & Whitney Canada PW150A turbopropeller engines
mounted on the wings. Each engine is equipped with a Dowty Aerospace
Model R408 propeller and is capable of delivering 5071 horsepower at
takeoff. The airplane is configured for five flight crewmembers and 78
passengers.
The Bombardier Model DHC-8-400 incorporates an unusual design
feature, the Automatic Takeoff Thrust Control System (ATTCS), referred
to by Bombardier as uptrim, to show compliance with the approach climb
requirements of Sec. 25.121(d). Appendix I to part 25 limits the
application of performance credit for ATTCS to takeoff only. Since the
airworthiness regulations do not contain appropriate safety standards
for approach climb performance using ATTCS, special conditions are
required to ensure a level of safety equivalent to that established in
the regulations.
Type Certification Basis
Under the provisions of Title 14, Code of Federal Regulations (14
CFR) Sec. 21.101, Bombardier must show that the Model DHC-8-400 meets
the applicable provisions of the regulations incorporated by reference
in Type Certificate No. A13NM or the applicable regulations in effect
on the date of application for the change to the Model DHC-8-400. The
regulations incorporated by reference in the type certificate are
commonly referred to as the ``original type certification basis.'' The
regulations incorporated by reference in Type Certificate No. A13NM are
as follows: part 25, effective February 1, 1965, including Amendments
25-1 through 25-86, and Sec. 25.109 as amended by Amendment 92. The
certification basis may also include later amendments to part 25 that
are not relevant to these special conditions. In addition, the
certification basis for the Model DHC-8-400 includes part 34, effective
September 10, 1990, including Amendment 34-3 effective February 3,
1999, plus any amendments in effect at the time of certification; and
part 36, effective December 1, 1969, including Amendments 36-1 through
36-21 and any subsequent amendments which will be applicable on the
date the type certificate is issued. These special conditions form an
additional part of the type certification basis. In addition, the
certification basis may include other special conditions that are not
relevant to these special conditions.
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 Bombardier Model DHC-8-400 because
of a novel or unusual design feature, special conditions are prescribed
under the provisions of Sec. 21.16.
In addition to the applicable airworthiness regulations and special
conditions, the Model DHC-8-400 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.
Special conditions, as appropriate, are issued in accordance with
Sec. 11.49 after public notice, as required by Secs. 11.28 and
11.29(b), and become part of the type certification basis in accordance
with Sec. 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 Sec. 21.101(a)(1).
Novel or Unusual Design Features
The Model DHC-8-400 will incorporate the following novel or unusual
design feature: the Automatic Takeoff Thrust Control System (ATTCS),
referred to by Bombardier as uptrim, to show compliance with the
approach climb requirements of Sec. 25.121(d). The Bombardier Model
DHC-8-400 is a medium-sized airplane powered by two Pratt & Whitney
Canada PW150A turbopropeller engines equipped with Full Authority
Digital Engine Controls (FADEC) that, in part, protect against
exceeding engine limits. The Model DHC-8-400 is also equipped with
Dowty Aerospace Model R408 propellers as part of the propulsion
package. The propellers incorporate a Propeller Electronic Control
(PEC) that functions with the FADEC to control the engine/propeller
system.
The Model DHC-8-400 incorporates a non-moving throttle system that
functions by placing the throttle levers in detents for the takeoff and
climb phases of flight, allowing the FADEC to schedule power settings
based on flight phase. With the uptrim and associated systems
functioning normally as designed, all applicable requirements of 14
CFR, part 25 and paragraph 25 of the Joint Aviation Requirements (JAR),
will be met without requiring any action by the crew to increase power.
Automatic takeoff power control on the Model DHC-8-400 involves
uptrimming the remaining engine to Maximum Takeoff Power (MTOP) and
autofeathering the propeller on the failed engine. These actions will
be controlled by the PEC. At takeoff when AUTOFEATHER (A/F) is selected
and the power levers are set to Normal Takeoff Power (NTOP), the engine
display will show an ``A/F ARM'' message. This engine display will
confirm to the pilot that the system is armed and autofeather and
uptrim will occur without any further action by the crew if an engine
fails. During go-around the uptrim will be automatically
[[Page 67702]]
armed as soon as the control (power) levers are set to the takeoff (go-
around) configuration.
Engine power is set to NTOP, which is 90 percent of MTOP, to
initiate the takeoff roll. The value of NTOP for the current ambient
conditions will be calculated and set by the FADEC. Following an engine
failure during takeoff or go-around, the ATTCS will change the power
reference on the operating engine to achieve the MTOP rating if the
engine power was originally set to NTOP. If the reduced power takeoff
option is being used the ATTCS will increase the power of the operating
engine from 90 percent to 100 percent of the corresponding set power.
The engine operating limits (turbine temperature and RPM) for NTOP
are set and displayed to the pilot when that rating is selected. These
limits are set such that the engine red line limits are not exceeded
when an uptrim is applied. When MTOP rating is selected or triggered,
the engine limits are reset automatically to reflect the engine red
line limits.
When both Power Lever Angles (PLA) are high and both the Condition
Lever Angles (CLA) are at maximum position (MAX), the system is armed.
If the torque on one engine drops below 25 percent, the PEC on the
failed engine sends an uptrim signal to the remaining engine. Other
conditions that will trigger the uptrim are the reduction of prop speed
(Np) below 80 percent or the automatic feathering of the prop. The
power levers will continue to function normally should the ATTCS fail.
The MTOP can also be selected by pressing the ``MTOP'' switch on the
engine control panel. The full MTOP is available if the pilot elects to
push the PLA past the takeoff power detent into the over travel range.
To deactivate the uptrim, the PLA's should be moved out of the
rating detent to a position less than 60 degrees (PLA not high) or the
CLA of the active engine should be moved out of the MAX/1020 takeoff
detent.
The part 25 standards for ATTCS, contained in Sec. 25.904 and
appendix I, specifically restrict performance credit for ATTCS to
takeoff. Expanding the scope of the standards to include other phases
of flight, including go-around, was considered at the time the
standards were issued, but flightcrew workload issues precluded further
consideration. As stated in the preamble to Amendment 25-62: ``In
regard to ATTCS credit for approach climb and go-around maneuvers,
current regulations preclude a higher thrust for the approach climb
(Sec. 25.121(d)) than for the landing climb (Sec. 25.119). The workload
required for the flightcrew to monitor and select from multiple in-
flight thrust settings in the event of an engine failure during a
critical point in the approach, landing, or go-around operations is
excessive. Therefore, the FAA does not agree that the scope of the
amendment should be changed to include the use of ATTCS for anything
except the takeoff phase'' (52 FR 43153, November 9, 1987).
The ATTCS incorporated on the Model DHC-8-400 allows the pilot to
use the same power setting procedure during a go-around, regardless of
whether or not an engine fails. In either case, the pilot obtains go-
around power by moving the throttles into the forward (takeoff/go-
around) throttle detent. Since the ATTCS is permanently armed, it will
function automatically following an engine failure, and advance the
remaining engine to the ATTCS thrust level. Therefore, this design
adequately addresses the pilot workload concerns identified in the
preamble to Amendment 25-62. Accordingly, these proposed special
conditions would require a showing of compliance with those provisions
of Sec. 25.904 and appendix I that are applicable to the approach climb
and go-around maneuvers.
The definition of a critical time interval for the approach climb
case, during which time it must be extremely improbable to violate a
flight path based on the Sec. 25.121(d) gradient requirement, is of
primary importance. The Sec. 25.121(d) gradient requirement implies a
minimum one-engine-inoperative flight path capability with the airplane
in the approach configuration. The engine may have been inoperative
before initiating the go-around, or it may become inoperative during
the go-around. The definition of the critical time interval must
consider both possibilities.
Discussion of Comments
Notice of Proposed Special Conditions No. 25-99-08-SC for the
Bombardier Model DHC-8-400 series airplanes was published in the
Federal Register on August 12, 1999 (64 FR 43943). Two commenters
responded to the Notice.
Comment: One commenter agrees that the applicable airworthiness
regulations do not contain appropriate safety standards for approach
climb performance using an Automatic Takeoff Thrust Control System
(ATTCS), and concurs with the proposed special conditions.
Disposition: The comment is accepted with no action required.
Comment: One commenter states that the proposed special condition
uses a complicated construction to determine a ``critical time
interval,'' broadly following the idea of Appendix I to JAR-25 for
ATTCS takeoffs, but having defined the time interval, the special
condition itself assigns it no regulatory function.
Disposition: The critical time interval concept used in the special
condition originated with Appendix I to part 25. Appendix I to part 25
remains in effect for the Model DHC-8-400. Therefore, Sec. I25.3, which
specifies the requirements associated with the critical time interval,
continues to apply. The combined failure of an engine and the ATTCS
must be extremely improbable during the critical time interval. Also,
an ATTCS failure or combination of failures during the critical time
interval shall not prevent the insertion of the maximum approved
takeoff thrust or power, or must be shown to be an improbable event. An
ATTCS failure or combination of failures during the critical time
interval shall not result in a significant loss or reduction in thrust
or power, or must be shown to be an extremely improbable event. No
changes were made to the proposed special condition as a result of this
comment.
Comment: One commenter states the proposed special condition
defines time periods for two different failure cases in an ATTCS go-
around (not the same as critical time intervals) whose permitted
duration is related to a period in the takeoff case (again, not the
critical time interval). However, the correlation with the takeoff case
seems weak; in the takeoff case, the effect of an engine failure plus
ATTCS failure in the critical time interval is clearly hazardous
(flight below the normal takeoff flight path) and an appropriate
probability target must be met in this interval. In the go-around case,
it just means the reduced gradient starts slightly earlier.
Disposition: The time periods referring to the takeoff case in the
definition of the critical time interval for go-around are associated
with the minimum acceptable time period for the flightcrew to recognize
the combined ATTCS and engine failure and to take corrective action by
manually inserting go-around thrust. Using the time interval from the
takeoff case for the time it takes the flightcrew to recognize and
respond makes use of an accepted benchmark and ensures consistent
treatment in the design and evaluation of the ATTCS for both takeoff
and go-around. The intent of the special condition is to ensure that
the flight path implied by the part 25 approach climb gradient
requirement is
[[Page 67703]]
maintained when an automatic system is used to increase thrust on the
operating engine when an engine fails. For both the takeoff and the go-
around cases, the intent is for compliance with the applicable part 25
performance requirements to continue to be met, considering the
potential for a concurrent ATTCS and engine failure. No changes were
made to the proposed special condition as a result of this comment.
Comment: One commenter states there are no criteria directly
associated with failures in the go-around critical time interval,
noting that the ``effect'' is variable depending on go-around height,
but surprisingly, the special condition deals only in terms of
gradients. This is presumably by analogy with the basic go-around
performance requirements, which are not tightly tied to obstacle
clearance, but it does make it difficult to understand the objective of
the special condition. Is it obstacle clearance or ground contact in
the go-around?
Disposition: The Appendix I to part 25 requirements related to the
critical time interval continue to apply for use of ATTCS in the go-
around phase of flight. The part 25 approach climb gradient, which is
the only applicable part 25 requirement for the use of ATTCS for go-
around, is independent of the go-around initiation height. The
objective of the special condition is to retain the performance
capability associated with the part 25 approach climb requirement,
which is not directly tied to either obstacle clearance or ground
contact in the go-around. No changes were made to the proposed special
condition as a result of this comment.
Comment: One commenter asks why the approach is assumed to be made
on a 2.5 degree glidepath.
Disposition: Two and one-half degrees were selected to
conservatively represent a normal approach glidepath, which is
typically 2.5 to 3 degrees. No changes were made to the proposed
special condition as a result of this comment.
Comment: One commenter notes that in the absence of any height
constraints, the construction of the flight paths for setting the
critical time interval could in theory involve flight below ground
level, but still give a valid interval. Would this be acceptable?
Disposition: The special condition ensures that the existing part
25 requirements are met for an airplane incorporating an ATTCS. Under
this special condition, the go-around flight path will not deviate
below that required by part 25. The operating requirements address the
relationship between this go-around flight path capability and the
surrounding terrain. No changes were made to the proposed special
condition as a result of this comment.
Comment: One commenter asks the purpose of the proposed special
condition.
Disposition: The special condition ensures that the existing part
25 requirements are met for an airplane incorporating an ATTCS.
Comment: One commenter asks what regulatory effect the proposed
special condition might have on design or performance scheduling.
Disposition: The special condition will affect the design of the
ATTCS to the extent that the system meets the reliability requirements
associated with the critical time interval for the go-around phase of
flight. The special condition will provide the flightcrew with a means
to verify, before beginning an approach for landing, that the ATTCS is
in a condition to operate. There will be no effect on performance
scheduling.
Comment: One commenter states that the absence of a defined point
of origin for the go-around makes the possible effects and safety
benefits of the proposed special condition hard to predict.
Disposition: The proposed special condition will ensure that the
relevant part 25 requirement associated with go-around, Sec. 25.121(d),
will continue to be met when a system is installed that automatically
increases power on the operating engine after an engine fails.
Therefore, the level of safety provided by the special condition for an
airplane with such a system installed is equivalent to that assured by
part 25 for airplanes that do not have such a system. No changes were
made to the proposed special condition as a result of this comment.
Applicability
As discussed above, these proposed special conditions would be
applicable to the Bombardier Model DHC-8-400. Should Bombardier apply
at a later date for a change to the type certificate to include another
model incorporating the same novel or unusual design feature, these
special conditions would apply to that model as well under the
provisions of Sec. 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 CASA Model
C-295 is imminent, the FAA finds that good cause exists to make these
special conditions effective upon issuance.
Conclusion
This action affects only certain novel or unusual design features
on the Bombardier Model DHC-8-400 airplane. 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 proposed 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 the Bombardier Regional Aircraft Model
DHC-8-400 airplane.
1. General. An Automatic Takeoff Thrust Control System (ATTCS) is
defined as the entire automatic system, including all devices, both
mechanical and electrical that sense engine failure, transmit signals,
actuate fuel controls or power levers, or increase engine power by
other means on operating engines to achieve scheduled thrust or power
increases and furnish cockpit information on system operation.
2. ATTCS. The engine power control system that automatically resets
the power or thrust on the operating engine (following engine failure
during the approach for landing) must comply with the following
requirements:
a. Performance and System Reliability Requirements. The probability
analysis must include consideration of ATTCS failure occurring after
the time at which the flightcrew last verifies that the ATTCS is in a
condition to operate until the beginning of the critical time interval.
b. Thrust Setting. The initial takeoff thrust set on each engine at
the beginning of the takeoff roll or go-around may not be less than:
(1) Ninety (90) percent of the thrust level set by the ATTCS (the
maximum takeoff thrust or power approved for the airplane under
existing ambient conditions);
(2) That required to permit normal operation of all safety-related
systems and equipment dependent upon engine thrust or power lever
position; or
[[Page 67704]]
(3) That shown to be free of hazardous engine response
characteristics when thrust is advanced from the initial takeoff thrust
or power to the maximum approved takeoff thrust or power.
c. Powerplant Controls. In addition to the requirements of
Sec. 25.1141, no single failure or malfunction, or probable combination
thereof, of the ATTCS, including associated systems, may cause the
failure of any powerplant function necessary for safety. The ATTCS must
be designed to:
(1) Apply thrust or power on the operating engine(s), following any
one engine failure during takeoff or go-around, to achieve the maximum
approved takeoff thrust or power without exceeding engine operating
limits; and
(2) Provide a means to verify to the flightcrew before takeoff and
before beginning an approach for landing that the ATTCS is in a
condition to operate.
3. Critical Time Interval. The definition of the Critical Time
Interval in appendix I, Sec. I25.2(b) shall be expanded to include the
following:
a. When conducting an approach for landing using ATTCS, the
critical time interval is defined as follows:
(1) The critical time interval begins at a point on a 2.5 degree
approach glide path from which, assuming a simultaneous engine and
ATTCS failure, the resulting approach climb flight path intersects a
flight path originating at a later point on the same approach path
corresponding to the part 25 one-engine-inoperative approach climb
gradient. The period of time from the point of simultaneous engine and
ATTCS failure to the intersection of these flight paths must be no
shorter than the time interval used in evaluating the critical time
interval for takeoff beginning from the point of simultaneous engine
and ATTCS failure and ending upon reaching a height of 400 feet.
(2) The critical time interval ends at the point on a minimum
performance, all-engines-operating go-around flight path from which,
assuming a simultaneous engine and ATTCS failure, the resulting minimum
approach climb flight path intersects a flight path corresponding to
the part 25 minimum one-engine-inoperative approach climb gradient. The
all-engines-operating go-around flight path and the part 25 one-engine-
inoperative approach climb gradient flight path originate from a common
point on a 2.5 degree approach path. The period of time from the point
of simultaneous engine and ATTCS failure to the intersection of these
flight paths must be no shorter than the time interval used in
evaluating the critical time interval for the takeoff beginning from
the point of simultaneous engine and ATTCS failure and ending upon
reaching a height of 400 feet.
b. The critical time interval must be determined at the altitude
resulting in the longest critical time interval for which one-engine-
inoperative approach climb performance data are presented in the
Airplane Flight Manual.
c. The critical time interval is illustrated in the following
figure:
[GRAPHIC] [TIFF OMITTED] TR03DE99.023
[[Page 67705]]
*The engine and ATTCS failed time interval must be no shorter
than the time interval from the point of simultaneous engine and
ATTCS failure to a height of 400 feet used to comply with I25.2(b)
for ATTCS use during takeoff.
Issued in Renton, Washington, on November 22, 1999.
Donald L. Riggin,
Acting Manager, Transport Airplane Directorate, Aircraft Certification
Service, ANM-100.
[FR Doc. 99-31396 Filed 12-2-99; 8:45 am]
BILLING CODE 4910-13-P