[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



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    *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