262 

14 CFR Ch. I (1–1–14 Edition) 

§ 23.841 

enough if it is of a design that reason-
ably 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 to indicate to the 

pilot the pressure differential, the 
cabin pressure altitude, and the rate of 
change of cabin pressure altitude. 

(6) Warning indication at the pilot 

station to indicate when the safe or 
preset pressure differential is exceeded 
and when a cabin pressure altitude of 
10,000 feet is exceeded. The 10,000 foot 
cabin altitude warning may be in-
creased up to 15,000 feet for operations 
from high altitude airfields (10,000 to 
15,000 feet) provided: 

(i) The landing or the take off modes 

(normal or high altitude) are clearly 
indicated to the flight crew. 

(ii) Selection of normal or high alti-

tude airfield mode requires no more 
than one flight crew action and goes to 
normal airfield mode at engine stop. 

(iii) The pressurization system is de-

signed to ensure cabin altitude does 
not exceed 10,000 feet when in flight 
above flight level (FL) 250. 

(iv) The pressurization system and 

cabin altitude warning system is de-
signed to ensure cabin altitude warning 
at 10,000 feet when in flight above 
FL250. 

(7) A warning placard for the pilot if 

the structure is not designed for pres-
sure differentials up to the maximum 
relief valve setting in combination 
with landing loads. 

(8) A means to stop rotation of the 

compressor or to divert airflow from 
the cabin if continued rotation of an 
engine-driven cabin compressor or con-
tinued flow of any compressor bleed air 
will create a hazard if a malfunction 
occurs. 

(c) If certification for operation 

above 41,000 feet and not more than 
45,000 feet is requested— 

(1) The airplane must prevent cabin 

pressure altitude from exceeding the 
following after decompression from 
any probable pressurization system 
failure in conjunction with any unde-
tected, latent pressurization system 
failure condition: 

(i) If depressurization analysis shows 

that the cabin altitude does not exceed 
25,000 feet, the pressurization system 
must prevent the cabin altitude from 
exceeding the cabin altitude-time his-
tory shown in Figure 1 of this section. 

(ii) Maximum cabin altitude is lim-

ited to 30,000 feet. If cabin altitude ex-
ceeds 25,000 feet, the maximum time 
the cabin altitude may exceed 25,000 
feet is 2 minutes; time starting when 
the cabin altitude exceeds 25,000 feet 
and ending when it returns to 25,000 
feet. 

(2) The airplane must prevent cabin 

pressure altitude from exceeding the 
following after decompression from 
any single pressurization system fail-
ure in conjunction with any probable 
fuselage damage: 

(i) If depressurization analysis shows 

that the cabin altitude does not exceed 
37,000 feet, the pressurization system 
must prevent the cabin altitude from 
exceeding the cabin altitude-time his-
tory shown in Figure 2 of this section. 

(ii) Maximum cabin altitude is lim-

ited to 40,000 feet. If cabin altitude ex-
ceeds 37,000 feet, the maximum time 
the cabin altitude may exceed 25,000 
feet is 2 minutes; time starting when 
the cabin altitude exceeds 25,000 feet 
and ending when it returns to 25,000 
feet. 

(3) In showing compliance with para-

graphs (c)(1) and (c)(2) of this section, 
it may be assumed that an emergency 
descent is made by an approved emer-
gency procedure. A 17-second flight 
crew recognition and reaction time 
must be applied between cabin altitude 
warning and the initiation of an emer-
gency descent. Fuselage structure, en-
gine and system failures are to be con-
sidered in evaluating the cabin decom-
pression. 

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