title-14-part-25-sec25-832

301

Federal Aviation Administration, DOT

§ 25.832

supplied to other compartments and
areas:

(1) The flight crew compartment.
(2) Crewmember compartments and

areas other than the flight crew com-
partment unless the crewmember com-
partment or area is ventilated by air
interchange with other compartments
or areas under all operating conditions.

(f) Means to enable the flight crew to

control the temperature and quantity
of ventilating air supplied to the flight
crew compartment independently of
the temperature and quantity of ven-
tilating air supplied to other compart-
ments are not required if all of the fol-
lowing conditions are met:

(1) The total volume of the flight

crew and passenger compartments is
800 cubic feet or less.

(2) The air inlets and passages for air

to flow between flight crew and pas-
senger compartments are arranged to
provide compartment temperatures
within 5 degrees F. of each other and
adequate ventilation to occupants in
both compartments.

(3) The temperature and ventilation

controls are accessible to the flight
crew.

(g) The exposure time at any given

temperature must not exceed the val-
ues shown in the following graph after
any improbable failure condition.

[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.

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,

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302

14 CFR Ch. I (1–1–24 Edition)

§ 25.833

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]

RESSURIZATION

§ 25.841

Pressurized cabins.

(a) Except as provided in paragraph

(c) of this section, pressurized cabins
and compartments to be occupied must
be equipped to provide a cabin pressure
altitude of not more than 8,000 feet
under normal operating conditions.

(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 except as
provided in paragraph (c) of this sec-
tion.

(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.

(3) Fuselage structure, engine and

system failures are to be considered in
evaluating the cabin decompression.

(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 equivalents) to
automatically prevent a negative pres-
sure differential that would damage
the structure. One valve is enough,
however, if it is of a design that rea-
sonably 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 at the pilot or flight

engineer station to show the pressure
differential, the cabin pressure alti-
tude, and the rate of change of the
cabin pressure altitude.

(6) Warning indication to the

flightcrew when the safe or preset pres-
sure differential or cabin pressure alti-
tude limit is exceeded. Appropriate
warning markings on the cabin pres-
sure differential indicator meet the
warning requirement for pressure dif-
ferential limits. An alert meets the
warning requirement for cabin pressure
altitude limits if it warns the
flightcrew when the cabin pressure al-
titude exceeds 10,000 feet, except as
provided in paragraph (d) of this sec-
tion.

(7) A warning placard at the pilot or

flight engineer station if the structure
is not designed for pressure differen-
tials up to the maximum relief valve
setting in combination with landing
loads.

(8) The pressure sensors necessary to

meet the requirements of paragraphs
(b)(5) and (b)(6) of this section and
§ 25.1447(c), must be located and the
sensing system designed so that, in the
event of loss of cabin pressure in any
passenger or crew compartment (in-
cluding upper and lower lobe galleys),
the warning and automatic presen-
tation devices, required by those provi-
sions, will be actuated without any
delay that would significantly increase
the hazards resulting from decompres-
sion.

ports with elevations at or above 8,000
feet, the cabin pressure altitude in
pressurized cabins and occupied com-
partments may be up to, or greater