CS 25.831  Ventilation

(See AMC 25.831)

(a)     Under normal operating conditions and in the event of any probable failure conditions of any system that 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 that contains at least 0.25 Kg (0.55 lb) of fresh air per minute. (See AMC 25.831(a).)

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

(1)     Carbon monoxide concentrations in excess of one 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% by volume (sea level equivalent) in compartments normally occupied by passengers or crewmembers. For the purpose of this subparagraph, “sea level equivalent” refers to conditions of 25° C (77° F) and 1 013·2 hPa (760 millimetres of mercury) pressure.

(c)      There must be provisions made to ensure that the conditions prescribed in sub-paragraph (b) of this paragraph are met after reasonably probable failures or malfunctioning of the ventilating, heating, pressurisation or other systems and equipment. (See AMC 25.831(c).)

(d)     If accumulation of hazardous quantities of smoke in the cockpit area is reasonably probable, smoke evacuation must be readily accomplished, starting with full pressurisation and without depressurising beyond safe limits.

(e)     Except as provided in sub-paragraph (f) of this paragraph, means must be provided to enable the occupants of the following compartments and areas to control the temperature and quantity of ventilating air supplied to their compartment or area independently of the temperature and quantity of air supplied to other compartments and areas:

(1)     The flight-crew compartment.

(2)     Crew-member compartments and areas other than the flight-crew compartment unless the crewmember compartment 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 ventilating air supplied to other compartments are not required if all of the following conditions are met:

(1)     The total volume of the flight-crew and passenger compartments is 22.65m³ (800 cubic ft) or less.

(2)     The air inlets and passages for air to flow between flight-crew and passenger compartments are arrange to provide compartment temperatures within 2.8°C (5°F) of each other and adequate ventilation to occupants in both compartments.

(3)     The temperature and ventilation controls are accessible to the flight crew.

[Amdt No: 25/18]

[Amdt No: 25/23]