261 

Federal Aviation Administration, DOT 

§ 23.841 

Number of pas-

senger seats 

Minimum main passenger aisle width 

Less than 25 

inches from floor 

25 inches and 

more from floor 

10 through 19 .......

9 inches ................

15 inches. 

(b) When certification to the emer-

gency exist provisions of § 23.807(d)(4) is 
requested, the main passenger aisle 
width at any point between the seats 
must equal or exceed the following val-
ues: 

Number of passenger seats 

Minimum main passenger 

aisle width (inches) 

Less than 
25 inches 

from floor 

25 inches 
and more 
from floor 

10 or fewer ................................

1

12 15 

11 through 19 ............................

12 

20 

1

A narrower width not less than 9 inches may be approved 

when substantiated by tests found necessary by the 
Administrator. 

[Amdt. 23–34, 52 FR 1831, Jan. 15, 1987, as 
amended by Amdt. 23–46, 59 FR 25774, May 17, 
1994] 

§ 23.831

Ventilation. 

(a) Each passenger and crew compart-

ment must be suitably ventilated. Car-
bon monoxide concentration may not 
exceed one part in 20,000 parts of air. 

(b) For pressurized airplanes, the 

ventilating air in the flightcrew and 
passenger compartments must be free 
of harmful or hazardous concentrations 
of gases and vapors in normal oper-
ations and in the event of reasonably 
probable failures or malfunctioning of 
the ventilating, heating, pressuriza-
tion, or other systems and equipment. 
If accumulation of hazardous quan-
tities of smoke in the cockpit area is 
reasonably probable, smoke evacuation 
must be readily accomplished starting 
with full pressurization and without 
depressurizing beyond safe limits. 

(c) For jet pressurized airplanes that 

operate at altitudes above 41,000 feet, 
under normal operating conditions and 
in the event of any probable failure 
conditions of any system which would 
adversely affect the ventilating air, the 
ventilation system must provide rea-
sonable passenger comfort. The ven-
tilation system must also provide a 
sufficient amount of uncontaminated 
air to enable the flight crew members 
to perform their duties without undue 
discomfort or fatigue. For normal oper-

ating conditions, the ventilation sys-
tem must be designed to provide each 
occupant with at least 0.55 pounds of 
fresh air per minute. In the event of 
the loss of one source of fresh air, the 
supply of fresh airflow may not be less 
than 0.4 pounds per minute for any pe-
riod exceeding five minutes. 

(d) For jet pressurized airplanes that 

operate at altitudes above 41,000 feet, 
other probable and improbable Envi-
ronmental Control System failure con-
ditions that adversely affect the pas-
senger and flight crew compartment 
environmental conditions may not af-
fect flight crew performance so as to 
result in a hazardous condition, and no 
occupant shall sustain permanent 
physiological harm. 

[Doc. No. 4080, 29 FR 17955, Dec. 18, 1964; 30 
FR 258, Jan. 9, 1965, as amended by Amdt. 23– 
34, 52 FR 1831, Jan. 15, 1987; Amdt. 23–42, 56 
FR 354, Jan. 3, 1991; Amdt. 23–62, 76 FR 75757, 
Dec. 2, 2011] 

P

RESSURIZATION

 

§ 23.841

Pressurized cabins. 

(a) If certification for operation 

above 25,000 feet is requested, the air-
plane must be able to maintain a cabin 
pressure altitude of not more than 
15,000 feet, in the event of any probable 
failure condition in the pressurization 
system. During decompression, the 
cabin altitude may not exceed 15,000 
feet for more than 10 seconds and 25,000 
feet for any duration. 

(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 equivalent) to 
automatically prevent a negative pres-
sure differential that would damage 
the structure. However, one valve is 

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