498 

14 CFR Ch. I (1–1–14 Edition) 

§ 25.1310 

(e) In showing compliance with para-

graphs (a) and (b) of this section with 
regard to the electrical system and 
equipment design and installation, 
critical environmental conditions must 
be considered. For electrical genera-
tion, distribution, and utilization 
equipment required by or used in com-
plying with this chapter, except equip-
ment covered by Technical Standard 
Orders containing environmental test 
procedures, the ability to provide con-
tinuous, safe service under foreseeable 
environmental conditions may be 
shown by environmental tests, design 
analysis, or reference to previous com-
parable service experience on other air-
craft. 

(f) EWIS must be assessed in accord-

ance with the requirements of § 25.1709. 

[Amdt. 25–23, 35 FR 5679, Apr. 8, 1970, as 
amended by Amdt. 25–38, 41 FR 55467, Dec. 20, 
1976; Amdt. 25–41, 42 FR 36970, July 18, 1977; 
Amdt. 25–123, 72 FR 63405, Nov. 8, 2007] 

§ 25.1310

Power source capacity and 

distribution. 

(a) Each installation whose func-

tioning is required for type certifi-
cation or under operating rules and 
that requires a power supply is an ‘‘es-
sential load’’ on the power supply. The 
power sources and the system must be 
able to supply the following power 
loads in probable operating combina-
tions and for probable durations: 

(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-engine air-

planes; and 

(ii) Any two engines on airplanes 

with three or more engines. 

(4) Essential loads for which an alter-

nate source of power is required, after 
any failure or malfunction in any one 
power supply system, distribution sys-
tem, or other utilization system. 

(b) In determining compliance with 

paragraphs (a)(2) and (3) of this section, 
the power loads may be assumed to be 
reduced under a monitoring procedure 
consistent with safety in the kinds of 
operation authorized. Loads not re-
quired in controlled flight need not be 
considered for the two-engine-inoper-

ative condition on airplanes with three 
or more engines. 

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

§ 25.1316

Electrical and electronic sys-

tem lightning protection. 

(a) Each electrical and electronic 

system that performs a function, for 
which failure would prevent the contin-
ued safe flight and landing of the air-
plane, must be designed and installed 
so that— 

(1) The function is not adversely af-

fected during and after the time the 
airplane is exposed to lightning; and 

(2) The system automatically recov-

ers normal operation of that function 
in a timely manner after the airplane 
is exposed to lightning. 

(b) Each electrical and electronic 

system that performs a function, for 
which failure would reduce the capa-
bility of the airplane or the ability of 
the flightcrew to respond to an adverse 
operating condition, must be designed 
and installed so that the function re-
covers normal operation in a timely 
manner after the airplane is exposed to 
lightning. 

[Doc. No. FAA–2010–0224, Amdt. 25–134, 76 FR 
33135, June 8, 2011] 

§ 25.1317

High-intensity Radiated 

Fields (HIRF) Protection. 

(a) Except as provided in paragraph 

(d) of this section, each electrical and 
electronic system that performs a func-
tion whose failure would prevent the 
continued safe flight and landing of the 
airplane must be designed and installed 
so that— 

(1) The function is not adversely af-

fected during and after the time the 
airplane is exposed to HIRF environ-
ment I, as described in appendix L to 
this part; 

(2) The system automatically recov-

ers normal operation of that function, 
in a timely manner, after the airplane 
is exposed to HIRF environment I, as 
described in appendix L to this part, 
unless the system’s recovery conflicts 
with other operational or functional 
requirements of the system; and 

(3) The system is not adversely af-

fected during and after the time the 

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