AMC 25.831(a) Ventilation

• ED Decision 2020/024/R found in: CS-25 Amdt 27 - Large Aeroplanes (Jan 2023)

AMC 25.831(a) Ventilation ED Decision 2020/024/R 1. General [CS 25.831(a)](#_DxCrossRefBm1709821304) specifies that the ventilation system must be designed to provide a minimum of 0.25 kg (0.55 lb) of fresh air per minute per person (i.e. 10 cubic feet per minute of air at 8 000 feet pressure altitude and at a cabin temperature of 24°C (75°F)) for normal operations. The applicant may demonstrate compliance with this specification by analysis, ground tests, and/or flight tests. Because it is not practicable to measure the airflow at each occupant’s location, the fresh air supplied per minute per occupant may be determined by averaging the total cabin fresh air supply and cockpit fresh air supply for the number of occupants that each area can accommodate, assuming a uniform ventilation distribution in each area. 2. Low airflow capability during some flight phases If an applicant proposes not to provide the minimum required fresh airflow during the phases of flight that use low power levels, the applicant must show that the cabin air quality is not compromised during those flight phases. 3. Operations with the air conditioning system ‘off’ The following provisions should be considered for the limited time periods, such as during take-off, during which the air conditioning system is ‘off’: a. There should be a means to annunciate to the flight crew that the air conditioning system is selected to ‘off’. When, in flight, after the end of the maximum allowed time period (e.g. typically after the take-off), the air conditioning system is still in the ‘off’ position, an alert should be triggered to inform the flight crew of the status of the air conditioning system. b. It should be demonstrated that the ventilation system continues to provide an acceptable environment in the passenger cabin and the cockpit for the brief period when the air conditioning system is not operating. c. Furthermore, the equipment environment should be evaluated during those periods to ensure that the reliability and performance of the equipment are not impaired. This evaluation should cover the extremes of ambient hot and cold air temperatures in which the aeroplane is expected to operate. d. In addition, it should be demonstrated that no unsafe condition will result from operation for a limited time with the air conditioning system ‘off’, if a fire occurs. When demonstrating compliance with [CS 25.831(d)](#_DxCrossRefBm1709821304) (cockpit smoke removal), [CS 25.857](#_DxCrossRefBm1709821309) (occupied areas smoke penetration), and [CS 25.858](#_DxCrossRefBm1709821308) (smoke detection), the following should be considered: i. During the operation of the aeroplane for any limited period of time with the air conditioning system ‘off’, the smoke detection systems should be effective. ii. It should be possible for the air conditioning system to be turned ‘on’ and returned to the approved air conditioning system ‘on’ configuration to extract any hazardous quantities of smoke. e. Finally, the period during which the aeroplane is operated with the air conditioning system ‘off’ is intended to be of short duration. Therefore, the maximum time period allowed for the operation of an aeroplane in this configuration should be defined by the applicant and specified in the appropriate operating manuals, along with any related operating procedures that are necessary to ensure that the above items are addressed. 4. Probable failure conditions For probable failure conditions, the ventilation system should be designed to provide enough fresh air to prevent the accumulation of odours and pollutants such as carbon dioxide. Under these conditions, the supply of fresh air should not be less than 0.18 kg/min (0·4 lb/min) per person for any period exceeding five minutes. However, temporary reductions below this flow rate may be accepted provided that the compartment environment can be maintained at a level which is not hazardous to the occupant; for this purpose, the applicant may refer to international cabin air quality standards. [Amdt 25/23] [Amdt 25/26]