JAR 25A903 Auxiliary power unit
(a) Each APU must meet the requirements of
JAR–APU for the corresponding category and
class of operation intended.
(c) Control of APU rotation and shut-down
capability
*Definitions of non-essential APUs and essential APUs are
given in JAR–APU.
(1) It shall be possible to shut down the
APU from the flight deck in normal and
emergency conditions.
(2) There must be a means for stopping
the rotation of any APU individually in flight,
except that the means of stopping the rotation
of any APU need be provided only where
continued rotation could jeopardise the safety
of the aeroplane. Each component of the
stopping system on the APU side of the
firewall that might be exposed to fire must be
at least fire-resistant.
(3) In particular, where no means is
provided to prevent continued rotation, the
safety of the aeroplane must be shown in the
event of failure of the APU oil supply.
(d) For APU installations:
(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 AMJ 20-128A.)]
(2) The power-plant systems associated
with APU control devices, systems, and instru-mentation,
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.
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