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14 CFR Ch. I (1–1–19 Edition) 

§ 25.1421 

show through analysis that the ice pro-
tection for the various components of 
the airplane is adequate, taking into 
account the various airplane oper-
ational configurations. To verify the 
analysis, one, or more as found nec-
essary, of the following methods must 
be used: 

(1) Laboratory dry air or simulated 

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

(2) Laboratory dry air or simulated 

icing tests, or a combination of both, of 
models of the airplane. 

(3) Flight tests of the airplane or its 

components in simulated icing condi-
tions, measured as necessary to sup-
port the analysis. 

(4) Flight tests of the airplane with 

simulated ice shapes. 

(5) Flight tests of the airplane in nat-

ural icing conditions, measured as nec-
essary to support the analysis. 

(c) For an airplane certified in ac-

cordance with paragraph (a)(2) or (3) of 
this section, the requirements of 
§ 25.1419(e), (f), (g), and (h) must be met 
for the icing conditions defined in Ap-
pendix O of this part in which the air-
plane is certified to operate. 

(d) For the purposes of this section, 

the following definitions apply: 


Reversible Flight Controls. 


controls in the normal operating con-
figuration that have force or motion 
originating at the airplane’s control 
surface (for example, through aero-
dynamic loads, static imbalance, or 
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. 


Simulated Icing Test. 

Testing con-

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


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, 

VerDate Sep<11>2014 

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