301 

Federal Aviation Administration, DOT 

§ 25.841 

[Doc. No. 5066, 29 FR 18291, Dec. 24, 1964, as amended by Amdt. 25–41, 42 FR 36970, July 18, 1977; 
Amdt. 25–87, 61 FR 28695, June 5, 1996; Amdt. 25–89, 61 FR 63956, Dec. 2, 1996] 

§ 25.832

Cabin ozone concentration. 

(a) The airplane cabin ozone con-

centration during flight must be shown 
not to exceed— 

(1) 0.25 parts per million by volume, 

sea level equivalent, at any time above 
flight level 320; and 

(2) 0.1 parts per million by volume, 

sea level equivalent, time-weighted av-
erage during any 3-hour interval above 
flight level 270. 

(b) For the purpose of this section, 

‘‘sea level equivalent’’ refers to condi-
tions of 25 

°

C and 760 millimeters of 

mercury pressure. 

(c) Compliance with this section 

must be shown by analysis or tests 
based on airplane operational proce-
dures and performance limitations, 
that demonstrate that either— 

(1) The airplane cannot be operated 

at an altitude which would result in 
cabin ozone concentrations exceeding 
the limits prescribed by paragraph (a) 
of this section; or 

(2) The airplane ventilation system, 

including any ozone control equipment, 
will maintain cabin ozone concentra-
tions at or below the limits prescribed 
by paragraph (a) of this section. 

[Amdt. 25–50, 45 FR 3883, Jan. 1, 1980, as 
amended by Amdt. 25–56, 47 FR 58489, Dec. 30, 
1982; Amdt. 25–94, 63 FR 8848, Feb. 23, 1998] 

§ 25.833

Combustion heating systems. 

Combustion heaters must be ap-

proved. 

[Amdt. 25–72, 55 FR 29783, July 20, 1990] 

P

RESSURIZATION

 

§ 25.841

Pressurized cabins. 

(a) Pressurized cabins and compart-

ments to be occupied must be equipped 
to provide a cabin pressure altitude of 
not more than 8,000 feet at the max-
imum operating altitude of the air-
plane under normal operating condi-
tions. 

(1) If certification for operation 

above 25,000 feet is requested, the air-
plane must be designed so that occu-
pants will not be exposed to cabin pres-
sure altitudes in excess of 15,000 feet 
after any probable failure condition in 
the pressurization system. 

(2) The airplane must be designed so 

that occupants will not be exposed to a 
cabin pressure altitude that exceeds 
the following after decompression from 
any failure condition not shown to be 
extremely improbable: 

(i) Twenty-five thousand (25,000) feet 

for more than 2 minutes; or 

(ii) Forty thousand (40,000) feet for 

any duration. 

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