title-14-part-25-sec25-1316

341

Federal Aviation Administration, DOT

§ 25.1316

of the crew to cope with adverse oper-
ating conditions is improbable.

vided to alert the crew to unsafe sys-
tem operating conditions, and to en-
able them to take appropriate correc-
tive action. Systems, controls, and as-
sociated monitoring and warning
means must be designed to minimize
crew errors which could create addi-
tional hazards.

(d) Compliance with the require-

ments 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, includ-

ing malfunctions and damage from ex-
ternal sources.

(2) The probability of multiple fail-

ures and undetected failures.

(3) The resulting effects on the air-

plane and occupants, considering the
stage of flight and operating condi-
tions, and

(4) The crew warning cues, corrective

action required, and the capability of
detecting faults.

(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

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14 CFR Ch. I (1–1–24 Edition)

§ 25.1317

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
airplane is exposed to HIRF environ-
ment II, as described in appendix L to
this part.

(b) Each electrical and electronic

system that performs a function whose
failure would significantly reduce the
capability of the airplane or the ability
of the flightcrew to respond to an ad-
verse operating condition must be de-
signed and installed so the system is
not adversely affected when the equip-
ment providing these functions is ex-
posed to equipment HIRF test level 1
or 2, as described in appendix L to this
part.

tem that performs a function whose
failure would reduce the capability of
the airplane or the ability of the
flightcrew to respond to an adverse op-
erating condition must be designed and
installed so the system is not adversely
affected when the equipment providing
the function is exposed to equipment
HIRF test level 3, as described in ap-
pendix L to this part.

(d) Before December 1, 2012, an elec-

trical or electronic system that per-
forms a function whose failure would
prevent the continued safe flight and

landing of an airplane may be designed
and installed without meeting the pro-
visions of paragraph (a) provided—

(1) The system has previously been

shown to comply with special condi-
tions for HIRF, prescribed under § 21.16,
issued before December 1, 2007;

(2) The HIRF immunity characteris-

tics of the system have not changed
since compliance with the special con-
ditions was demonstrated; and

(3) The data used to demonstrate

compliance with the special conditions
is provided.

[Doc. No. FAA–2006–23657, 72 FR 44025, Aug. 6,
2007]

NSTRUMENTS

: I

NSTALLATION

§ 25.1321

Arrangement and visibility.

(a) Each flight, navigation, and pow-

erplant instrument for use by any pilot
must be plainly visible to him from his
station with the minimum practicable
deviation from his normal position and
line of vision when he is looking for-
ward along the flight path.

(b) The flight instruments required

by § 25.1303 must be grouped on the in-
strument panel and centered as nearly
as practicable about the vertical plane
of the pilot’s forward vision. In addi-
tion—

(1) The instrument that most effec-

tively indicates attitude must be on
the panel in the top center position;

(2) The instrument that most effec-

tively indicates airspeed must be adja-
cent to and directly to the left of the
instrument in the top center position:

(3) The instrument that most effec-

tively indicates altitude must be adja-
cent to and directly to the right of the
instrument in the top center position;
and

(4) The instrument that most effec-

tively indicates direction of flight
must be adjacent to and directly below
the instrument in the top center posi-
tion.

must be closely grouped on the instru-
ment panel. In addition—

(1) The location of identical power-

plant instruments for the engines must
prevent confusion as to which engine
each instrument relates; and

(2) Powerplant instruments vital to

the safe operation of the airplane must