Aircraft Module - Air System Operations


The aircraft manufacturers recommend maximizing total cabin airflow and care should be taken to avoid blocking air vents (particularly along the floor). These are general recommendations for cabin air considerations and there may be exceptions for specific aircraft models. It is strongly recommended that operators consult with the aircraft OEM for questions specific to an aircraft type.


Ground Operations (before chocks-off and after chocks-in)​

  • Operations without the air conditioning packs or external pre-conditioned air (PCA) source should be avoided. External air sources are not processed through a high-efficiency particulate air (HEPA) filter. Use of the aircraft APU should be permitted at the gate to enable the aircraft's air conditioning system to be operated, if equivalent filtration from PCA is not available.
  • If the aircraft has an air recirculation system, but does not have HEPA filters installed, reference should be made to OEM published documents or the OEM should be contacted to determine the recirculation system setting.
  • It is recommended that fresh air and recirculation systems be operated to exchange the volume of cabin air before boarding considering the following:
    • For aircraft with air conditioning, run the air conditioning packs (with bleed air provided by APU or engines) or supply air via external PCA source at least 10 minutes prior to the boarding process, throughout boarding and during disembarkation.
    • For aircraft with HEPA filters, run the recirculation system to maximize flow through the filters.
    • For aircraft without an air conditioning system, keep aircraft doors open during turnaround time to facilitate cabin air exchange (passengers' door, service door and cargo door).

Flight Operations

  • Operate environmental control systems with all Packs in AUTO and recirculation fans on.
    • Valid only if HEPA recirculation air filters are confirmed to be installed.
  •  If non-HEPA filters are installed, contact the aircraft OEM for recommendations on recirculation settings.
  •  If the aircraft in-flight operating procedure calls for packs to be off for take-off, the packs should be switched back on as soon as thrust performance allows.

Minimum Equipment List (MEL) Dispatch:

  • Fully operational air conditioning packs and recirculation fans provide the best overall cabin ventilation performance. It is recommended to minimize dispatch with packs inoperative. It is recommended to minimize dispatch with recirculation fans inoperative for aircraft equipped with HEPA filter. 
  • Some aircraft have better airflow performance with all outflow valves operational. The OEM should be contacted about ventilation performance of the aircraft with outflow valves inoperative and the limitations associated with the dispatch in this situation.

High Flow (max Bleed) Switch:

  • If the aircraft has an option for high flow operation, contact the OEM for setting recommendations. For example:

Boeing recommends that airlines select High Flow Mode for 747-8, MD-80 and MD-90 aircraft, as this will maximize total ventilation rate in the cabin.


Note 1.- This will increase fuel burn. However, for the 747-400 and 737, High Flow Mode should NOT be selected as this does not result in an increase in total ventilation rate. For all models, recirculation fans should remain on (when HEPA filters are installed).


Note 2.- Sick passenger positioning guidance is contained in Cabin Crew element of the Crew module.

Filter Maintenance:

  • Follow normal maintenance procedures as specified by the OEM. Take note of special protection and handling of filters when changing them.
  • Contact OEM or refer to OEM published document to check if an additional sanitization procedure and/or personnel health protection is needed to avoid microbiological contamination in the filter replacement area.

Means for uniform implementation

  • OEM communication through International Coordinating Council of Aerospace Industries Associations (ICCAIA) and OEM communication with airlines.
  • Use the Aircraft COVID-19 Disinfection Control Sheet (PHC Form 2) or a similar one when appropriate.


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