JAR 25.1309 Equipment, systems and
installations
(a) The equipment, systems, and installations
whose functioning is required by the JAR and
national operating regulations must be designed to
ensure that they perform their intended functions
under any foreseeable operating conditions. (See
AMJ 25.1309 and ACJ No. 2 to JAR 25.1309.)
However, systems used for non-essential services
need only comply so far as is necessary to ensure
that the installations are neither a source of danger
in themselves nor liable to prejudice the proper
functioning of any essential service.
(b) The aeroplane systems and associated
components, considered separately and in relation
to other systems, must be designed so that (see
AMJ 25.1309 and ACJ No. 3 to JAR 25.1309 and
AMJ 25.1309(b)) –
(1) The occurrence of any failure
condition which would prevent the continued
safe flight and landing of the aeroplane is
extremely improbable; and
(2) The occurrence of any other failure
condition which would reduce the capability of
the aeroplane or the ability of the crew to cope
with adverse operating conditions is
improbable.
(c) Warning information must be provided to
alert the crew to unsafe system operating
conditions, and to enable them to take appropriate
corrective action. Systems, controls, and
associated monitoring and warning means must be
designed to minimise crew errors which could
create additional hazards. (See AMJ 25.1309 and
ACJ Nos. 4 and 8 to JAR 25.1309.)
(d) Compliance with the requirements of sub-paragraph
(b) of this paragraph must be shown by
analysis, and where necessary, by appropriate
ground, flight, or simulator tests. The analysis
must consider (see AMJ 25.1309) –
(1) Possible modes of failure, including
malfunctions and damage from external
sources;
(2) The probability of multiple failures
and undetected failures;
(3) The resulting effects on the
aeroplane and occupants, considering the stage
of flight and operating conditions; and
(4) The crew warning cues, corrective
action required, and the capability of detecting
faults.
(e) Each installation whose functioning is
required for certification and that requires a
power supply, is an ‘essential load’ on the power
supply. The power sources and the system must
be able to supply the following power loads in
probable operating combinations and for probable
durations (see ACJ No. 6 to JAR 25.1309);
(1) Loads connected to the system with
the system functioning normally.
(2) Essential loads, after failure of any
one prime mover, power converter, or energy
storage device.
(3) Essential loads after failure of –
(i) Any one engine on two-engined
aeroplanes; and
(ii) Any two engines on three-or-more
engined aeroplanes.
After the failure of any two engines on a three-engined
aeroplane, those services essential to
airworthiness must continue to function and
perform adequately within the limits of operation
implied by the emergency conditions. (See ACJ
No. 7 to JAR 25.1309.)
(4) Essential loads for which an
alternate source of power is required by any
applicable JAR or national operating
regulations, after any failure or malfunction in
any one power supply system, distribution
system, or other utilisation system.
(f) In determining compliance with sub-paragraphs
(e)(2) and (3) of this paragraph, the
power loads may be assumed to be reduced under
a monitoring procedure consistent with safety in
the kinds of operation authorised. Loads not
required in controlled flight need not be
considered for the two-engine-inoperative
condition on aeroplanes with three or more
engines.
(g) In showing compliance with sub-paragraphs
(a) and (b) of this paragraph with
regard to system and equipment design and
installation, critical environmental conditions
including vibration and acceleration loads,
handling by personnel and where appropriate fluid
pressure effects, must be considered. For power
generation, distribution and utilisation equipment
required by or used for certification, the ability to
provide continuous safe service under foreseeable
environmental conditions may be shown by
environmental tests, design analysis or reference
to previous comparable service experience on
other aeroplanes.
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