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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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