Section 25.1310

14 CFR Ch. I (1-1-19 Edition)

of the crew to cope with adverse operating conditions is improbable.
(c) Warning information must be provided to alert the crew to unsafe system operating conditions, and to enable them to take appropriate corrective action. Systems, controls, and associated monitoring and warning
means must be designed to minimize
crew errors which could create additional hazards.
(d) Compliance with the requirements of paragraph (b) of this section
must be shown by analysis, and where
necessary, by appropriate ground,
flight, or simulator tests. The analysis
must consider - 
(1) Possible modes of failure, including malfunctions and damage from external sources.
(2) The probability of multiple failures and undetected failures.
(3) The resulting effects on the airplane and occupants, considering the
stage of flight and operating conditions, and
(4) The crew warning cues, corrective
action required, and the capability of
detecting faults.
(e) In showing compliance with paragraphs (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 generation, distribution, and utilization
equipment required by or used in complying with this chapter, except equipment covered by Technical Standard
Orders containing environmental test
procedures, the ability to provide continuous, safe service under foreseeable
environmental conditions may be
shown by environmental tests, design
analysis, or reference to previous comparable service experience on other aircraft.
(f) EWIS must be assessed in accordance with the requirements of Section 25.1709.

spaschal on DSK3GDR082PROD with CFR

[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]

Section 25.1310 Power source capacity and
distribution.
(a) Each installation whose functioning is required for type certification or under operating rules and

that requires a power supply is an  - essential load -  on the power supply. The
power sources and the system must be
able to supply the following power
loads in probable operating combinations 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 airplanes; and
(ii) Any two engines on airplanes
with three or more engines.
(4) Essential loads for which an alternate source of power is required, after
any failure or malfunction in any one
power supply system, distribution system, 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 required in controlled flight need not be
considered for the two-engine-inoperative condition on airplanes with three
or more engines.
[Amdt. 25-123, 72 FR 63405, Nov. 8, 2007]

Section 25.1316 Electrical and electronic system lightning protection.
(a) Each electrical and electronic
system that performs a function, for
which 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 affected during and after the time the
airplane is exposed to lightning; and
(2) The system automatically recovers 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 capability 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 recovers normal operation in a timely

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