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350 

14 CFR Ch. I (1–1–24 Edition) 

§ 25.1355 

(4) No corrosive fluids or gases that 

may escape from the battery may dam-
age surrounding airplane structures or 
adjacent essential equipment. 

(5) Each nickel cadmium battery in-

stallation must have provisions to pre-
vent any hazardous effect on structure 
or essential systems that may be 
caused by the maximum amount of 
heat the battery can generate during a 
short circuit of the battery or of indi-
vidual cells. 

(6) Nickel cadmium battery installa-

tions must have— 

(i) A system to control the charging 

rate of the battery automatically so as 
to prevent battery overheating; 

(ii) A battery temperature sensing 

and over-temperature warning system 
with a means for disconnecting the 
battery from its charging source in the 
event of an over-temperature condi-
tion; or 

(iii) A battery failure sensing and 

warning system with a means for dis-
connecting the battery from its charg-
ing source in the event of battery fail-
ure. 

(c) Electrical bonding must provide 

an adequate electrical return path 
under both normal and fault condi-
tions, on airplanes having grounded 
electrical systems. 

[Amdt. 25–123, 72 FR 63405, Nov. 8, 2007] 

§ 25.1355

Distribution system. 

(a) The distribution system includes 

the distribution busses, their associ-
ated feeders, and each control and pro-
tective device. 

(b) [Reserved] 
(c) If two independent sources of elec-

trical power for particular equipment 
or systems are required by this chap-
ter, in the event of the failure of one 
power source for such equipment or 
system, another power source (includ-
ing its separate feeder) must be auto-
matically provided or be manually se-
lectable to maintain equipment or sys-
tem operation. 

[Doc. No. 5066, 29 FR 18291, Dec. 24, 1964, as 
amended by Amdt. 25–23, 35 FR 5679, Apr. 8, 
1970; Amdt. 25–38, 41 FR 55468, Dec. 20, 1976] 

§ 25.1357

Circuit protective devices. 

(a) Automatic protective devices 

must be used to minimize distress to 

the electrical system and hazard to the 
airplane in the event of wiring faults or 
serious malfunction of the system or 
connected equipment. 

(b) The protective and control de-

vices in the generating system must be 
designed to de-energize and disconnect 
faulty power sources and power trans-
mission equipment from their associ-
ated busses with sufficient rapidity to 
provide protection from hazardous 
over-voltage and other malfunctioning. 

(c) Each resettable circuit protective 

device must be designed so that, when 
an overload or circuit fault exists, it 
will open the circuit irrespective of the 
position of the operating control. 

(d) If the ability to reset a circuit 

breaker or replace a fuse is essential to 
safety in flight, that circuit breaker or 
fuse must be located and identified so 
that it can be readily reset or replaced 
in flight. Where fuses are used, there 
must be spare fuses for use in flight 
equal to at least 50% of the number of 
fuses of each rating required for com-
plete circuit protection. 

(e) Each circuit for essential loads 

must have individual circuit protec-
tion. However, individual protection 
for each circuit in an essential load 
system (such as each position light cir-
cuit in a system) is not required. 

(f) For airplane systems for which 

the ability to remove or reset power 
during normal operations is necessary, 
the system must be designed so that 
circuit breakers are not the primary 
means to remove or reset system power 
unless specifically designed for use as a 
switch. 

(g) Automatic reset circuit breakers 

may be used as integral protectors for 
electrical equipment (such as thermal 
cut-outs) if there is circuit protection 
to protect the cable to the equipment. 

[Doc. No. 5066, 29 FR 18291, Dec. 24, 1964, as 
amended by Amdt. 25–123, 72 FR 63405, Nov. 8, 
2007] 

§ 25.1360

Precautions against injury. 

(a) Shock. The electrical system 

must be designed to minimize risk of 
electric shock to crew, passengers, and 
servicing personnel and to mainte-
nance personnel using normal pre-
cautions. 

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351 

Federal Aviation Administration, DOT 

§ 25.1383 

(b) Burns. The temperature of any 

part that may be handled by a crew-
member during normal operations 
must not cause dangerous inadvertent 
movement by the crewmember or in-
jury to the crewmember. 

[Amdt. 25–123, 72 FR 63406, Nov. 8, 2007] 

§ 25.1362

Electrical supplies for emer-

gency conditions. 

A suitable electrical supply must be 

provided to those services required for 
emergency procedures after an emer-
gency landing or ditching. The circuits 
for these services must be designed, 
protected, and installed so that the 
risk of the services being rendered inef-
fective under these emergency condi-
tions is minimized. 

[Amdt. 25–123, 72 FR 63406, Nov. 8, 2007] 

§ 25.1363

Electrical system tests. 

(a) When laboratory tests of the elec-

trical system are conducted— 

(1) The tests must be performed on a 

mock-up using the same generating 
equipment used in the airplane; 

(2) The equipment must simulate the 

electrical characteristics of the dis-
tribution wiring and connected loads to 
the extent necessary for valid test re-
sults; and 

(3) Laboratory generator drives must 

simulate the actual prime movers on 
the airplane with respect to their reac-
tion to generator loading, including 
loading due to faults. 

(b) For each flight condition that 

cannot be simulated adequately in the 
laboratory or by ground tests on the 
airplane, flight tests must be made. 

§ 25.1365

Electrical appliances, motors, 

and transformers. 

(a) Domestic appliances must be de-

signed and installed so that in the 
event of failures of the electrical sup-
ply or control system, the require-
ments of § 25.1309(b), (c), and (d) will be 
satisfied. Domestic appliances are 
items such as cooktops, ovens, coffee 
makers, water heaters, refrigerators, 
and toilet flush systems that are 
placed on the airplane to provide serv-
ice amenities to passengers. 

(b) Galleys and cooking appliances 

must be installed in a way that mini-
mizes risk of overheat or fire. 

(c) Domestic appliances, particularly 

those in galley areas, must be installed 
or protected so as to prevent damage or 
contamination of other equipment or 
systems from fluids or vapors which 
may be present during normal oper-
ation or as a result of spillage, if such 
damage or contamination could create 
a hazardous condition. 

(d) Unless compliance with § 25.1309(b) 

is provided by the circuit protective 
device required by § 25.1357(a), electric 
motors and transformers, including 
those installed in domestic systems, 
must have a suitable thermal protec-
tion device to prevent overheating 
under normal operation and failure 
conditions, if overheating could create 
a smoke or fire hazard. 

[Amdt. 25–123, 72 FR 63406, Nov. 8, 2007] 

L

IGHTS

 

§ 25.1381

Instrument lights. 

(a) The instrument lights must— 
(1) Provide sufficient illumination to 

make each instrument, switch and 
other device necessary for safe oper-
ation easily readable unless sufficient 
illumination is available from another 
source; and 

(2) Be installed so that— 
(i) Their direct rays are shielded from 

the pilot’s eyes; and 

(ii) No objectionable reflections are 

visible to the pilot. 

(b) Unless undimmed instrument 

lights are satisfactory under each ex-
pected flight condition, there must be a 
means to control the intensity of illu-
mination. 

[Doc. No. 5066, 29 FR 18291, Dec. 24, 1964, as 
amended by Amdt. 25–72, 55 FR 29785, July 20, 
1990] 

§ 25.1383

Landing lights. 

(a) Each landing light must be ap-

proved, and must be installed so that— 

(1) No objectionable glare is visible 

to the pilot; 

(2) The pilot is not adversely affected 

by halation; and 

(3) It provides enough light for night 

landing. 

(b) Except when one switch is used 

for the lights of a multiple light instal-
lation at one location, there must be a 
separate switch for each light. 

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