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Federal Aviation Administration, DOT 

§ 25.1433 

trim or servo tab inputs) that is trans-
mitted back to flight deck controls. 
This term refers to flight deck controls 
connected to the pitch, roll, or yaw 
control surfaces by direct mechanical 
linkages, cables, or push-pull rods in 
such a way that pilot effort produces 
motion or force about the hinge line. 

(2)  Simulated Icing Test. Testing con-

ducted in simulated icing conditions, 
such as in an icing tunnel or behind an 
icing tanker. 

(3) Simulated Ice Shape. Ice shape fab-

ricated from wood, epoxy, or other ma-
terials by any construction technique. 

[Amdt. 25–140, 79 FR 65528, Nov. 4, 2014] 

§ 25.1421


If a megaphone is installed, a re-

straining means must be provided that 
is capable of restraining the mega-
phone when it is subjected to the ulti-
mate inertia forces specified in 
§ 25.561(b)(3). 

[Amdt. 25–41, 42 FR 36970, July 18, 1977] 

§ 25.1423

Public address system. 

A public address system required by 

this chapter must— 

(a) Be powerable when the aircraft is 

in flight or stopped on the ground, 
after the shutdown or failure of all en-
gines and auxiliary power units, or the 
disconnection or failure of all power 
sources dependent on their continued 
operation, for— 

(1) A time duration of at least 10 min-

utes, including an aggregate time dura-
tion of at least 5 minutes of announce-
ments made by flight and cabin crew-
members, considering all other loads 
which may remain powered by the 
same source when all other power 
sources are inoperative; and 

(2) An additional time duration in its 

standby state appropriate or required 
for any other loads that are powered by 
the same source and that are essential 
to safety of flight or required during 
emergency conditions. 

(b) Be capable of operation within 3 

seconds from the time a microphone is 
removed from its stowage. 

(c) Be intelligible at all passenger 

seats, lavatories, and flight attendant 
seats and work stations. 

(d) Be designed so that no unused, 

unstowed microphone will render the 
system inoperative. 

(e) Be capable of functioning inde-

pendently of any required crewmember 
interphone system. 

(f) Be accessible for immediate use 

from each of two flight crewmember 
stations in the pilot compartment. 

(g) For each required floor-level pas-

senger emergency exit which has an ad-
jacent flight attendant seat, have a 
microphone which is readily accessible 
to the seated flight attendant, except 
that one microphone may serve more 
than one exit, provided the proximity 
of the exits allows unassisted verbal 
communication between seated flight 

[Doc. No. 26003, 58 FR 45229, Aug. 26, 1993, as 
amended by Amdt. 25–115, 69 FR 40527, July 2, 






§ 25.1431

Electronic equipment. 

(a) In showing compliance with 

§ 25.1309 (a) and (b) with respect to 
radio and electronic equipment and 
their installations, critical environ-
mental conditions must be considered. 

(b) Radio and electronic equipment 

must be supplied with power under the 
requirements of § 25.1355(c). 

(c) Radio and electronic equipment, 

controls, and wiring must be installed 
so that operation of any one unit or 
system of units will not adversely af-
fect the simultaneous operation of any 
other radio or electronic unit, or sys-
tem of units, required by this chapter. 

(d) Electronic equipment must be de-

signed and installed such that it does 
not cause essential loads to become in-
operative as a result of electrical 
power supply transients or transients 
from other causes. 

[Doc. No. 5066, 29 FR 18291, Dec. 24, 1964, as 
amended by Amdt. 25–113, 69 FR 12530, Mar. 
16, 2004] 

§ 25.1433

Vacuum systems. 

There must be means, in addition to 

the normal pressure relief, to auto-
matically relieve the pressure in the 
discharge lines from the vacuum air 

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