303 

Federal Aviation Administration, DOT 

§ 25.851 

than, the airport elevation by 2,000 
feet, provided— 

(1) In the event of probable failure 

conditions of the cabin pressurization 
system, the cabin pressure altitude 
must not exceed 15,000 feet, or 2,000 feet 
above the airport elevation, whichever 
is higher; and 

(2) The cabin pressurization system is 

designed to minimize the time in flight 
that occupants may be exposed to 
cabin pressure altitudes exceeding 8,000 
feet. 

(d) When operating into or out of air-

ports with elevations at or above 8,000 
feet, the cabin pressure high altitude 
warning alert may be provided at up to 
15,000 feet, or 2,000 feet above the air-
plane’s maximum takeoff and landing 
altitude, whichever is greater, pro-
vided: 

(1) During landing, the change in 

cabin pressure high altitude warning 
alert may not occur before the start of 
descent into the high elevation airport 
and, following takeoff, the cabin pres-
sure high altitude warning alert must 
be reset to 10,000 feet before beginning 
cruise operation; 

(2) Indication is provided to the 

flightcrew that the cabin pressure high 
altitude warning alert has shifted 
above 10,000 feet cabin pressure alti-
tude; and 

(3) Either an alerting system is in-

stalled that notifies the flightcrew 
members on flight deck duty when to 
don oxygen in accordance with the ap-
plicable operating regulations, or a 
limitation is provided in the airplane 
flight manual that requires the pilot 
flying the airplane to don oxygen when 
the cabin pressure altitude warning has 
shifted above 10,000 feet, and requires 
other flightcrew members on flight 
deck duty to monitor the cabin pres-
sure and utilize oxygen in accordance 
with the applicable operating regula-
tions. 

[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; 
Amdt. No. 25–151, 88 FR 39160, June 15, 2023; 
88 FR 44032, July 11, 2023] 

§ 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 
extinguishers must be conveniently lo-
cated and evenly distributed in pas-
senger compartments: 

Passenger capacity 

No. of extinguishers 

7 through 30 ...............................

1 

31 through 60 .............................

2 

61 through 200 ...........................

3 

201 through 300 ............................

4 

301 through 400 ............................

5 

401 through 500 ............................

6 

501 through 600 ............................

7 

601 through 700 ............................

8 

(2) At least one hand fire extin-

guisher must be conveniently located 
in the pilot compartment. 

(3) At least one readily accessible 

hand fire extinguisher must be avail-
able for use in each Class A or Class B 
cargo or baggage compartment and in 
each Class E or Class F cargo or bag-
gage compartment that is accessible to 
crewmembers in flight. 

(4) At least one hand fire extin-

guisher must be located in, or readily 

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