302 

14 CFR Ch. I (1–1–19 Edition) 

§ 25.843 

(3) Fuselage structure, engine and 

system failures are to be considered in 
evaluating the cabin decompression. 

(b) Pressurized cabins must have at 

least the following valves, controls, 
and indicators for controlling cabin 
pressure: 

(1) Two pressure relief valves to auto-

matically limit the positive pressure 
differential to a predetermined value 
at the maximum rate of flow delivered 
by the pressure source. The combined 
capacity of the relief valves must be 
large enough so that the failure of any 
one valve would not cause an appre-
ciable rise in the pressure differential. 
The pressure differential is positive 
when the internal pressure is greater 
than the external. 

(2) Two reverse pressure differential 

relief valves (or their equivalents) to 
automatically prevent a negative pres-
sure differential that would damage 
the structure. One valve is enough, 
however, if it is of a design that rea-
sonably precludes its malfunctioning. 

(3) A means by which the pressure 

differential can be rapidly equalized. 

(4) An automatic or manual regulator 

for controlling the intake or exhaust 
airflow, or both, for maintaining the 
required internal pressures and airflow 
rates. 

(5) Instruments at the pilot or flight 

engineer station to show the pressure 
differential, the cabin pressure alti-
tude, and the rate of change of the 
cabin pressure altitude. 

(6) Warning indication at the pilot or 

flight engineer station to indicate 
when the safe or preset pressure dif-
ferential and cabin pressure altitude 
limits are exceeded. Appropriate warn-
ing markings on the cabin pressure dif-
ferential indicator meet the warning 
requirement for pressure differential 
limits and an aural or visual signal (in 
addition to cabin altitude indicating 
means) meets the warning requirement 
for cabin pressure altitude limits if it 
warns the flight crew when the cabin 
pressure altitude exceeds 10,000 feet. 

(7) A warning placard at the pilot or 

flight engineer station if the structure 
is not designed for pressure differen-
tials up to the maximum relief valve 
setting in combination with landing 
loads. 

(8) The pressure sensors necessary to 

meet the requirements of paragraphs 
(b)(5) and (b)(6) of this section and 
§ 25.1447(c), must be located and the 
sensing system designed so that, in the 
event of loss of cabin pressure in any 
passenger or crew compartment (in-
cluding upper and lower lobe galleys), 
the warning and automatic presen-
tation devices, required by those provi-
sions, will be actuated without any 
delay that would significantly increase 
the hazards resulting from decompres-
sion. 

[Doc. No. 5066, 29 FR 18291, Dec. 24, 1964, as 
amended by Amdt. 25–38, 41 FR 55466, Dec. 20, 
1976; Amdt. 25–87, 61 FR 28696, June 5, 1996] 

§ 25.843

Tests for pressurized cabins. 

(a) 

Strength test. 

The complete pres-

surized cabin, including doors, win-
dows, and valves, must be tested as a 
pressure vessel for the pressure dif-
ferential specified in § 25.365(d). 

(b) 

Functional tests. 

The following 

functional tests must be performed: 

(1) Tests of the functioning and ca-

pacity of the positive and negative 
pressure differential valves, and of the 
emergency release valve, to stimulate 
the effects of closed regulator valves. 

(2) Tests of the pressurization system 

to show proper functioning under each 
possible condition of pressure, tem-
perature, and moisture, up to the max-
imum altitude for which certification 
is requested. 

(3) Flight tests, to show the perform-

ance of the pressure supply, pressure 
and flow regulators, indicators, and 
warning signals, in steady and stepped 
climbs and descents at rates cor-
responding to the maximum attainable 
within the operating limitations of the 
airplane, up to the maximum altitude 
for which certification is requested. 

(4) Tests of each door and emergency 

exit, to show that they operate prop-
erly after being subjected to the flight 
tests prescribed in paragraph (b)(3) of 
this section. 

F

IRE

P

ROTECTION

 

§ 25.851

Fire extinguishers. 

(a) 

Hand fire extinguishers. 

(1) The fol-

lowing minimum number of hand fire 

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