349
Federal Aviation Administration, DOT
§ 25.1353
E
LECTRICAL
S
YSTEMS AND
E
QUIPMENT
§ 25.1351
General.
(a)
Electrical system capacity. The re-
quired generating capacity, and num-
ber and kinds of power sources must—
(1) Be determined by an electrical
load analysis; and
(2) Meet the requirements of § 25.1309.
(b)
Generating system. The generating
system includes electrical power
sources, main power busses, trans-
mission 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 main-
tained within the limits for which the
equipment is designed, during any
probable operating condition; and
(4) System transients due to switch-
ing, fault clearing, or other causes do
not make essential loads inoperative,
and do not cause a smoke or fire haz-
ard.
(5) There are means accessible, in
flight, to appropriate crewmembers for
the individual and collective dis-
connection of the electrical power
sources from the system.
(6) There are means to indicate to ap-
propriate crewmembers 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 airplane, and that external power
can be electrically connected to equip-
ment other than that used for engine
starting, means must be provided to
ensure that no external power supply
having a reverse polarity, or a reverse
phase sequence, can supply power to
the airplane’s electrical system.
(d)
Operation without normal electrical
power. It must be shown by analysis,
tests, or both, that the airplane can be
operated safely in VFR conditions, for
a period of not less than five minutes,
with the normal electrical power (elec-
trical power sources excluding the bat-
tery) inoperative, with critical type
fuel (from the standpoint of flameout
and restart capability), and with the
airplane initially at the maximum cer-
tificated altitude. Parts of the elec-
trical system may remain on if—
(1) A single malfunction, including a
wire bundle or junction box fire, can-
not result in loss of both the part
turned off and the part turned on; and
(2) The parts turned on are elec-
trically and mechanically isolated
from the parts turned off.
[Doc. No. 5066, 29 FR 18291, Dec. 24, 1964, as
amended by Amdt. 25–41, 42 FR 36970, July 18,
1977; Amdt. 25–72, 55 FR 29785, July 20, 1990]
§ 25.1353
Electrical equipment and in-
stallations.
(a) Electrical equipment and controls
must be installed so that operation of
any one unit or system of units will
not adversely affect the simultaneous
operation of any other electrical unit
or system essential to safe operation.
Any electrical interference likely to be
present in the airplane must not result
in hazardous effects on the airplane or
its systems.
(b) Storage batteries must be de-
signed and installed as follows:
(1) Safe cell temperatures and pres-
sures must be maintained during any
probable charging or discharging con-
dition. No uncontrolled increase in cell
temperature may result when the bat-
tery is recharged (after previous com-
plete discharge)—
(i) At maximum regulated voltage or
power;
(ii) During a flight of maximum dura-
tion; and
(iii) Under the most adverse cooling
condition likely to occur in service.
(2) Compliance with paragraph (b)(1)
of this section must be shown by test
unless experience with similar bat-
teries and installations has shown that
maintaining safe cell temperatures and
pressures presents no problem.
(3) No explosive or toxic gases emit-
ted by any battery in normal oper-
ation, or as the result of any probable
malfunction in the charging system or
battery installation, may accumulate
in hazardous quantities within the air-
plane.
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