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 crewmembers 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
(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
(c) There must be provisions made to
ensure that the conditions prescribed in paragraph (b) of this section are
met after reasonably probable failures or malfunctioning of the
ventilating, heating, pressurization, or other systems and equipment.
(d) If accumulation of hazardous
quantities of smoke in the cockpit area is reasonably probable, smoke
evacuation must be readily accomplished, starting with full pressurization
and without depressurizing beyond safe limits.
(e) Except as provided in paragraph (f)
of this section, 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
(1) The flight crew compartment.
(2) Crewmember 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 800 cubic feet or less.
(2) The air inlets and passages for air
to flow between flight crew and passenger 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 values shown in the following graph after
any improbable failure condition.