512 

14 CFR Ch. I (1–1–14 Edition) 

§ 25.1421 

operational configurations, in meas-
ured natural atmospheric icing condi-
tions and, as found necessary, by one 
or more of the following means: 

(1) Laboratory dry air or simulated 

icing tests, or a combination of both, of 
the components or models of the com-
ponents. 

(2) Flight dry air tests of the ice pro-

tection system as a whole, or of its in-
dividual components. 

(3) Flight tests of the airplane or its 

components in measured simulated 
icing conditions. 

(c) Caution information, such as an 

amber caution light or equivalent, 
must be provided to alert the 
flightcrew when the anti-ice or de-ice 
system is not functioning normally. 

(d) For turbine engine powered air-

planes, the ice protection provisions of 
this section are considered to be appli-
cable primarily to the airframe. For 
the powerplant installation, certain ad-
ditional provisions of subpart E of this 
part may be found applicable. (e) One 
of the following methods of icing detec-
tion and activation of the airframe ice 
protection system must be provided: 

(1) A primary ice detection system 

that automatically activates or alerts 
the flightcrew to activate the airframe 
ice protection system; 

(2) A definition of visual cues for rec-

ognition of the first sign of ice accre-
tion on a specified surface combined 
with an advisory ice detection system 
that alerts the flightcrew to activate 
the airframe ice protection system; or 

(3) Identification of conditions con-

ducive to airframe icing as defined by 
an appropriate static or total air tem-
perature and visible moisture for use 
by the flightcrew to activate the air-
frame ice protection system. 

(f) Unless the applicant shows that 

the airframe ice protection system 
need not be operated during specific 
phases of flight, the requirements of 
paragraph (e) of this section are appli-
cable to all phases of flight. 

(g) After the initial activation of the 

airframe ice protection system— 

(1) The ice protection system must be 

designed to operate continuously; 

(2) The airplane must be equipped 

with a system that automatically cy-
cles the ice protection system; or 

(3) An ice detection system must be 

provided to alert the flightcrew each 
time the ice protection system must be 
cycled. 

(h) Procedures for operation of the 

ice protection system, including acti-
vation and deactivation, must be estab-
lished and documented in the Airplane 
Flight Manual. 

[Amdt. 25–72, 55 FR 29785, July 20, 1990, as 
amended by Amdt. 25–121, 72 FR 44669, Aug. 8, 
2007; Amdt. 25–129, 74 FR 38339, Aug. 3, 2009] 

§ 25.1421

Megaphones. 

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. 

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