Appendix I to Part 25 - Installation of an Automatic Takeoff Thrust Control System (ATTCS)
14:1.0.1.3.12.12.121.1.14 : Appendix I
Appendix I to Part 25 - Installation of an Automatic Takeoff Thrust
Control System (ATTCS) I25.1
General.
(a) This appendix specifies additional requirements for
installation of an engine power control system that automatically
resets thrust or power on operating engine(s) in the event of any
one engine failure during takeoff.
(b) With the ATTCS and associated systems functioning normally
as designed, all applicable requirements of Part 25, except as
provided in this appendix, must be met without requiring any action
by the crew to increase thrust or power.
I25.2
Definitions.
(a) Automatic Takeoff Thrust Control System (ATTCS). An
ATTCS is defined as the entire automatic system used on takeoff,
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.
(b) Critical Time Interval. When conducting an ATTCS
takeoff, the critical time interval is between V1 minus 1 second
and a point on the minimum performance, all-engine flight path
where, assuming a simultaneous occurrence of an engine and ATTCS
failure, the resulting minimum flight path thereafter intersects
the Part 25 required actual flight path at no less than 400 feet
above the takeoff surface. This time interval is shown in the
following illustration:
I25.3
Performance and System Reliability Requirements.
The applicant must comply with the performance and ATTCS
reliability requirements as follows:
(a) An ATTCS failure or a combination of failures in the ATTCS
during the critical time interval:
(1) Shall not prevent the insertion of the maximum approved
takeoff thrust or power, or must be shown to be an improbable
event.
(2) Shall not result in a significant loss or reduction in
thrust or power, or must be shown to be an extremely improbable
event.
(b) The concurrent existence of an ATTCS failure and an engine
failure during the critical time interval must be shown to be
extremely improbable.
(c) All applicable performance requirements of Part 25 must be
met with an engine failure occurring at the most critical point
during takeoff with the ATTCS system functioning.
I25.4
Thrust Setting.
The initial takeoff thrust or power setting on each engine at
the beginning of the takeoff roll may not be less than any of the
following:
(a) Ninety (90) percent of the thrust or power set by the ATTCS
(the maximum takeoff thrust or power approved for the airplane
under existing ambient conditions);
(b) That required to permit normal operation of all
safety-related systems and equipment dependent upon engine thrust
or power lever position; or
(c) That shown to be free of hazardous engine response
characteristics when thrust or power is advanced from the initial
takeoff thrust or power to the maximum approved takeoff thrust or
power.
I25.5
Powerplant Controls.
(a) In addition to the requirements of § 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.
(b) The ATTCS must be designed to:
(1) Apply thrust or power on the operating engine(s), following
any one engine failure during takeoff, to achieve the maximum
approved takeoff thrust or power without exceeding engine operating
limits;
(2) Permit manual decrease or increase in thrust or power up to
the maximum takeoff thrust or power approved for the airplane under
existing conditions through the use of the power lever. For
airplanes equipped with limiters that automatically prevent engine
operating limits from being exceeded under existing ambient
conditions, other means may be used to increase the thrust or power
in the event of an ATTCS failure provided the means is located on
or forward of the power levers; is easily identified and operated
under all operating conditions by a single action of either pilot
with the hand that is normally used to actuate the power levers;
and meets the requirements of § 25.777 (a), (b), and (c);
(3) Provide a means to verify to the flightcrew before takeoff
that the ATTCS is in a condition to operate; and
(4) Provide a means for the flightcrew to deactivate the
automatic function. This means must be designed to prevent
inadvertent deactivation.
I25.6
Powerplant Instruments.
In addition to the requirements of § 25.1305:
(a) A means must be provided to indicate when the ATTCS is in
the armed or ready condition; and
(b) If the inherent flight characteristics of the airplane do
not provide adequate warning that an engine has failed, a warning
system that is independent of the ATTCS must be provided to give
the pilot a clear warning of any engine failure during takeoff.
[Amdt. 25-62, 52 FR 43156, Nov. 9, 1987]