CS 25J901 Installation

ED Decision 2016/010/R

(See AMC 25J901)

(a) For the purpose of this subpart, the APU installation includes:

 (1) The APU;

 (2) Each component that affects the control of the APU;

 (3) Each component that affects the safety of the APU.

(b) For the purpose of this subpart,

 (1) An essential APU is defined as an APU whose function is required for the dispatch of the aeroplane and/or continued safe flight.

 (2) A non-essential APU is defined as an APU whose function is a matter of convenience, either on the ground or in flight, and may be shut down without jeopardising safe aeroplane operation.

(c) For each APU:

 (1) The installation must comply with:

(i) The installation instructions provided under CS-APU, and

(ii) The applicable provisions of this subpart for non-essential APUs, or

(iii) The applicable provisions of this subpart for essential APUs.

 (2) The components of the installation must be constructed, arranged, and installed so as to ensure their continued safe operation between normal inspections or overhauls. (See AMC 25J901(c)(2).)

 (3) The installation must be accessible for necessary inspections and maintenance; and

 (4) The major components of the installation must be electrically bonded to the other parts of the aeroplane. (See AMC 25J901(c)(4).)

(d) The APU installation must comply with CS 25.1309, except that the effects of the following need not comply with CS 25.1309(b) (see AMC 25.901(c)):

 (1) APU case burn through or rupture; and

 (2)  Uncontained APU rotor failure.

[Amdt 25/1]

[Amdt 25/18]

AMC 25J901(c)(2) Assembly of Components

ED Decision 2005/006/R

The objectives of CS 25.671(b) should be satisfied with respect to APU systems, where the safety of the aeroplane could otherwise be jeopardised.

[Amdt 25/1]

AMC 25J901(c)(4) Electrical Bonding

ED Decision 2005/006/R

Where the APU is not in direct electrical contact with its mounting the engine should be electrically connected to the main earth system by at least two removable primary conductors, one on each side of the APU.

[Amdt 25/1]

CS 25J903 Auxiliary power unit

ED Decision 2005/006/R

(a) Each APU must meet the appropriate requirements of CS-APU for its intended function:

 (1) Essential: Category 1 APU,

 (2) Non-essential: Category 1 or Category 2 APU.

(b) Reserved

(c) Control of APU rotation and shut-down capability.

 (1) It shall be possible to shut down the APU from the flight deck in normal and emergency conditions.

 (2) Where continued rotation of an APU could jeopardise the safety of the aeroplane, there must be a means for stopping rotation. Each component of the stopping system located in the APU compartment must be at least fire resistant.

(d) For APU installation:

 (1) Design precautions must be taken to minimise the hazards to the aeroplane in the event of an APU rotor failure or of a fire originating within the APU which burns through the APU casing. (See AMC 20-128A.)

 (2) The systems associated with APU control devices, systems and instrumentation, must be designed to give reasonable assurance that those APU operating limitations that adversely affect turbine rotor structural integrity will not be exceeded in service.

(e) In-flight start capability.

 (1) For non-essential APUs that can be started in-flight and all essential APUs:

(i) Means must be provided to start the APU in-flight, and

(ii) An altitude and airspeed envelope must be established and demonstrated for APU in-flight starting.

 (2) For essential APUs:

 Cold soak must be considered in establishing the envelope of CS 25J903(e)(1)(ii).

[Amdt 25/1]

CS 25J939 APU operating characteristics

ED Decision 2005/006/R

(a)  APU operating characteristics must be investigated in all aeroplane operating conditions from APU start until shutdown to determine that no adverse characteristics (such as stall, surge, or flame-out) are present, to a hazardous degree, during normal and emergency operation within the range of operation limitations of the aeroplane and of the APU.

(b)  Reserved

(c)  The APU air inlet system may not, as a result of air-flow distortion during normal operation, cause vibration harmful to the APU.

(d)  It must be established over the range of operating conditions for which certification is required, that the APU installation vibratory conditions do not exceed the critical frequencies and amplitudes established under CS-APU 120.

[Amdt 25/1]

CS 25J943 Negative acceleration

ED Decision 2005/006/R

No hazardous malfunction of an APU or any component or system associated with the APU may occur when the aeroplane is operated at the negative accelerations within the flight envelopes prescribed in CS 25.333. This must be shown for the greatest duration expected for the acceleration.

[Amdt 25/1]

AMC 25J943 APU Operating Characteristics

ED Decision 2005/006/R

1 Compliance with CS 25J943 should be shown by design analysis and flight tests. The flight tests should include manoeuvre in which less than zero 'g' occurs for one continuous period of at least 5 seconds and a further manoeuvre with two periods of less than zero 'g' with a total time for these two periods of at least 5 seconds.

2 In the case of non-essential APUs, inadvertent shut-down due to negative accelerations is acceptable.

[Amdt 25/1]