Federal Aviation Administration, DOT

Section 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]

Section 25.833

Cabin ozone concentration.

(a) The airplane cabin ozone concentration 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 average during any 3-hour interval above
flight level 270.
(b) For the purpose of this section,
 - sea level equivalent -  refers to conditions of 25 SectionC and 760 millimeters of
mercury pressure.
(c) Compliance with this section
must be shown by analysis or tests
based on airplane operational procedures 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 concentrations 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]

Combustion heating systems.

Combustion
proved.

heaters

must

be

ap-

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

PRESSURIZATION
Section 25.841

Pressurized cabins.

(a) Pressurized cabins and compartments to be occupied must be equipped
to provide a cabin pressure altitude of
not more than 8,000 feet at the maximum operating altitude of the airplane under normal operating conditions.
(1) If certification for operation
above 25,000 feet is requested, the airplane must be designed so that occupants will not be exposed to cabin pressure 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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Section 25.832