547 

Federal Aviation Administration, DOT 

§ 27.1321 

in a timely manner after the rotorcraft 
is exposed to lightning. 

(b) For rotorcraft approved for in-

strument flight rules operation, each 
electrical and electronic system that 
performs a function, for which failure 
would reduce the capability of the 
rotorcraft or the ability of the 
flightcrew to respond to an adverse op-
erating condition, must be designed 
and installed so that the function re-
covers normal operation in a timely 
manner after the rotorcraft is exposed 
to lightning. 

[Doc. No. FAA–2010–0224, Amdt. 27–46, 76 FR 
33135, June 8, 2011] 

§ 27.1317

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 
rotorcraft must be designed and in-
stalled so that— 

(1) The function is not adversely af-

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

(2) The system automatically recov-

ers normal operation of that function, 
in a timely manner, after the rotor-
craft is exposed to HIRF environment 
I, as described in appendix D to this 
part, unless this conflicts with other 
operational or functional requirements 
of that system; 

(3) The system is not adversely af-

fected during and after the time the 
rotorcraft is exposed to HIRF environ-
ment II, as described in appendix D to 
this part; and 

(4) Each function required during op-

eration under visual flight rules is not 
adversely affected during and after the 
time the rotorcraft is exposed to HIRF 
environment III, as described in appen-
dix D to this part. 

(b) Each electrical and electronic 

system that performs a function whose 
failure would significantly reduce the 
capability of the rotorcraft or the abil-
ity of the flightcrew to respond to an 
adverse operating condition must be 
designed 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 D to this 
part. 

(c) Each electrical and electronic sys-

tem that performs a function whose 
failure would reduce the capability of 
the rotorcraft or the ability of the 
flightcrew to respond to an adverse op-
erating condition, must be designed 
and installed so the system is not ad-
versely affected when the equipment 
providing these functions is exposed to 
equipment HIRF test level 3, as de-
scribed in appendix D 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 a rotorcraft 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 44026, Aug. 6, 
2007] 

I

NSTRUMENTS

: I

NSTALLATION

 

§ 27.1321

Arrangement and visibility. 

(a) Each flight, navigation, and pow-

erplant instrument for use by any pilot 
must be easily visible to him. 

(b) For each multiengine rotorcraft, 

identical powerplant instruments must 
be located so as to prevent confusion as 
to which engine each instrument re-
lates. 

(c) Instrument panel vibration may 

not damage, or impair the readability 
or accuracy of, any instrument. 

(d) If a visual indicator is provided to 

indicate malfunction of an instrument, 

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