title-14-part-25-sec25-841

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

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§ 25.851

than, the airport elevation by 2,000
feet, provided—

(1) In the event of probable failure

conditions of the cabin pressurization
system, the cabin pressure altitude
must not exceed 15,000 feet, or 2,000 feet
above the airport elevation, whichever
is higher; and

(2) The cabin pressurization system is

designed to minimize the time in flight
that occupants may be exposed to
cabin pressure altitudes exceeding 8,000
feet.

(d) When operating into or out of air-

ports with elevations at or above 8,000
feet, the cabin pressure high altitude
warning alert may be provided at up to
15,000 feet, or 2,000 feet above the air-
plane’s maximum takeoff and landing
altitude, whichever is greater, pro-
vided:

(1) During landing, the change in

cabin pressure high altitude warning
alert may not occur before the start of
descent into the high elevation airport
and, following takeoff, the cabin pres-
sure high altitude warning alert must
be reset to 10,000 feet before beginning
cruise operation;

(2) Indication is provided to the

flightcrew that the cabin pressure high
altitude warning alert has shifted
above 10,000 feet cabin pressure alti-
tude; and

(3) Either an alerting system is in-

stalled that notifies the flightcrew
members on flight deck duty when to
don oxygen in accordance with the ap-
plicable operating regulations, or a
limitation is provided in the airplane
flight manual that requires the pilot
flying the airplane to don oxygen when
the cabin pressure altitude warning has
shifted above 10,000 feet, and requires
other flightcrew members on flight
deck duty to monitor the cabin pres-
sure and utilize oxygen in accordance
with the applicable operating regula-
tions.

[Doc. No. 5066, 29 FR 18291, Dec. 24, 1964, as
amended by Amdt. 25–38, 41 FR 55466, Dec. 20,
1976; Amdt. 25–87, 61 FR 28696, June 5, 1996;
Amdt. No. 25–151, 88 FR 39160, June 15, 2023;
88 FR 44032, July 11, 2023]

§ 25.843

Tests for pressurized cabins.

(a)

Strength test. The complete pres-

surized cabin, including doors, win-
dows, and valves, must be tested as a

pressure vessel for the pressure dif-
ferential specified in § 25.365(d).

(b)

Functional tests. The following

functional tests must be performed:

(1) Tests of the functioning and ca-

pacity of the positive and negative
pressure differential valves, and of the
emergency release valve, to stimulate
the effects of closed regulator valves.

(2) Tests of the pressurization system

to show proper functioning under each
possible condition of pressure, tem-
perature, and moisture, up to the max-
imum altitude for which certification
is requested.

(3) Flight tests, to show the perform-

ance of the pressure supply, pressure
and flow regulators, indicators, and
warning signals, in steady and stepped
climbs and descents at rates cor-
responding to the maximum attainable
within the operating limitations of the
airplane, up to the maximum altitude
for which certification is requested.

(4) Tests of each door and emergency

exit, to show that they operate prop-
erly after being subjected to the flight
tests prescribed in paragraph (b)(3) of
this section.

IRE

ROTECTION

§ 25.851

Fire extinguishers.

(a)

Hand fire extinguishers. (1) The fol-

lowing minimum number of hand fire
extinguishers must be conveniently lo-
cated and evenly distributed in pas-
senger compartments:

Passenger capacity

No. of extinguishers

7 through 30 ...............................

31 through 60 .............................

61 through 200 ...........................

201 through 300 ............................

301 through 400 ............................

401 through 500 ............................

501 through 600 ............................

601 through 700 ............................

(2) At least one hand fire extin-

guisher must be conveniently located
in the pilot compartment.

(3) At least one readily accessible

hand fire extinguisher must be avail-
able for use in each Class A or Class B
cargo or baggage compartment and in
each Class E or Class F cargo or bag-
gage compartment that is accessible to
crewmembers in flight.

(4) At least one hand fire extin-

guisher must be located in, or readily