341 

Federal Aviation Administration, DOT 

§ 25.1321 

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. 

(c) Each electrical and electronic sys-

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] 

I

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. 

(c) Required powerplant instruments 

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 

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