JAR 25.1351 General
(a) Electrical system capacity. The required
generating capacity, and number and kinds of
power sources must –
(1) Be determined by an electrical load
analysis; and
(2) Meet the requirements of JAR
25.1309.
(b) Generating system. The generating
system includes electrical power sources, main
power busses, transmission cables, and associated
control, regulation, and protective devices. It
must be designed so that –
(1) Power sources function properly
when independent and when connected in
combination;
(2) No failure or malfunction of any
power source can create a hazard or impair the
ability of remaining sources to supply essential
loads;
(3) The system voltage and frequency
(as applicable) at the terminals of all essential
load equipment can be maintained within the
limits for which the equipment is designed,
during any probable operating condition;
(4) System transients due to switching,
fault clearing, or other causes do not make
essential loads inoperative, and do not cause a
smoke or fire hazard;
(5) There are means accessible where
necessary, in flight, to appropriate crew
members for the individual and rapid
disconnection of each electrical power source
(see ACJ 25.1351(b)(5)); and
(6) There are means to indicate to
appropriate crew members the generating
system quantities essential for the safe
operation of the system, such as the voltage
and current supplied by each generator.
(c) External power. If provisions are made
for connecting external power to the aeroplane,
and that external power can be electrically
connected to equipment other than that used for
engine starting, means must be provided to ensure
that no external power supply having a reverse
polarity, a reverse phase sequence (including
crossed phase and neutral), open circuit line,
incorrect frequency or over-voltage, can supply
power to the aeroplane’s electrical system.
(d) Operation without normal electrical
power. (See ACJ 25.1351 (d).) The following
apply:
(1) Unless it can be shown that the loss
of the normal electrical power generating
system(s) is Extremely Improbable, alternate
high integrity electrical power system(s),
independent of the normal electrical power
generating system(s), must be provided to
power those services necessary to complete a
flight and make a safe landing.
(2) The services to be powered must
include –
(i) Those required for immediate
safety and which must continue to operate
following the loss of the normal electrical
power generating system(s), without the
need for flight crew action;
(ii) Those required for continued
controlled flight; and
(iii) Those required for descent,
approach and landing.
(3) Failures, including junction box,
control panel or wire bundle fires, which would
result in the loss of the normal and alternate
systems must be shown to be Extremely
Improbable.
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