SEC. 25.831. VENTILATION.

(a)

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 be designed to provide a sufficient amount of uncontaminated air to enable the crew members to perform their duties without undue discomfort or fatigue and to provide reasonable passenger comfort. For normal operating conditions, the ventilation system must be designed to provide each occupant with an airflow containing at least 0.55 pounds of fresh air per minute.

(b)

Crew and passenger compartment air must be free from harmful or hazardous concentrations of gases or vapors. In meeting this requirement, the following apply:

1.

Carbon monoxide concentrations in excess of 1 part in 20,000 parts of air are considered hazardous. For test purposes, any acceptable carbon monoxide detection method may be used.

2.

Carbon dioxide concentration during flight must be shown not to exceed 0.5 percent by volume (sea level equivalent) in compartments normally occupied by passengers or crew members.

[Doc. No. 5066, 29 FR18291, 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]

SEC. 25.832. 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 deg. C 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]

SEC. 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.

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 automatically 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 appreciable 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 pressure differential that would damage the structure. One valve is enough, however, if it is of a design that reasonably 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 altitude, and the rate of change of the cabin pressure altitude.

6.

Warning indication at the pilot or flight engineer station to indicate when the safe or preset pressure differential and cabin pressure altitude limits are exceeded. Appropriate warning markings on the cabin pressure differential indicator meet the warning requirement for pressure differential limits and an aural or visual signal (in addition to cabin altitude indicating means) meets the warning requirement for cabin pressure altitude limits if it warns the flight crew when the cabin pressure altitude exceeds 10,000 feet.

7.

A warning placard at the pilot or flight engineer station if the structure is not designed for pressure differentials 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 Sec. 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 (including upper and lower lobe galleys), the warning and automatic presentation devices, required by those provisions, will be actuated without any delay that would significantly increase the hazards resulting from decompression.

[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]

SEC. 121.219. VENTILATION.

Each passenger or crew compartment must be suitably ventilated. Carbon monoxide concentration may not be more than one part in 20,000 parts of air, and fuel fumes may not be present. In any case where partitions between compartments have louvres or other means allowing air to flow between compartments, there must be a means convenient to the crew for closing the flow of air through the partitions, when necessary.

SEC. 121.578. CABIN OZONE CONCENTRATION.

(a)

For the purpose of this section, the following definitions apply:

1.

“Flight segment” means scheduled nonstop flight time between two airports.

2.

“Sea level equivalent” refers to conditions of 25 deg. C and 760 millimeters of mercury pressure.

(b)

Except as provided in paragraphs (d) and (e) of this section, no certificate holder may operate an airplane above the following flight levels unless it is successfully demonstrated to the Administrator that the concentration of ozone inside the cabin will not exceed (1) for flight above flight level 320, 0.25 parts per million by volume, sea level equivalent, at any time above that flight level; and (2) for flight above flight level 270, 0.1 parts per million by volume, sea level equivalent, time-weighted average for each flight segment that exceeds 4 hours and includes flight above that flight level. (For this purpose, the amount of ozone below flight level 180 is considered to be zero.)

(c)

Compliance with this section must be shown by analysis or tests, based on either airplane operational procedures and performance limitations or the certificate holder's operations. The analysis or tests must show either of the following:

1.

Atmospheric ozone statistics indicate, with a statistical confidence of at least 84%, that at the altitudes and locations at which the airplane will be operated, cabin ozone concentrations will not exceed the limits prescribed by paragraph (b) of this section.

2.

The airplane ventilation system including any ozone control equipment, will maintain cabin ozone concentrations at or below the limits prescribed by paragraph (b) of this section.

(d)

A certificate holder may obtain an authorization to deviate from the requirements of paragraph (b) of this section, by an amendment to its operations specifications, if (1) it shows that due to circumstances beyond its control or to unreasonable economic burden it cannot comply for a specified period of time; and (2) it has submitted a plan acceptable to the Administrator to effect compliance to the extent possible.

(e)

A certificate holder need not comply with the requirements of paragraph (b) of this section for an aircraft (1) when the only persons carried are flight crewmembers and persons listed in Sec. 121.583; (2) if the aircraft is scheduled for retirement before January 1, 1985; or (3) if the aircraft is scheduled for re-engining under the provisions of Subpart E of Part 91, until it is re-engined.

[Doc. No. 121–154, 45 FR 3883, Jan. 21, 1980. Redesignated by Amdt. 121–162, 45 FR 46739, July 10, 1980; Amdt. 121–181, 47 FR 58489, Dec. 30, 1982; Amdt. 121–251, 60 FR 65935, Dec. 20, 1995]

SEC. 125.117. VENTILATION.

Each passenger or crew compartment must be suitably ventilated. CO concentration may not be more than 1 part in 20,000 parts of air, and fuel fumes may not be present. In any case where partitions between compartments have louvres or other means allowing air to flow between compartments, there must be a means convenient to the crew for closing the flow of air through the partitions when necessary.