It is a common misconception amongst some passengers that when onboard a flight, they are all sharing ‘stale air’. At this time, with the fear of coronavirus rife, it is important to challenge that misconception and help the public understand the way cabin air works. At the same time, we can look at other measures that could be helpful in preventing the spread of coronavirus when on board an aircraft.

Where does cabin air come from and how does it flow?

Cabin air is a mix of fresh air drawn from outside of the aircraft (treated prior to entering the cabin so that it is at a pressure and temperature comfortable for breathing) and existing cabin air that has been recycled through extremely efficient filters (known as High Efficiency Particulate Air (HEPA) filters) that are capable of trapping microscopic sized viruses such as SARS-Cov-2 (the novel coronavirus which causes COVID-19). Tests have shown HEPA filters to have an efficiency level of better than 99.97% and they provide air that meets the standards set for hospital operating theatres. In normal operation, less than half of the air is filtered and recirculated, the rest is fresh air drawn-in from outside the aircraft.

Air supplied to the cabin enters at the level of the overhead compartments (from above and below them) and is extracted at floor level. This means that the air is drawn down and, importantly, there is no flow forward or aft along the cabin. The treated air supplied to aircraft toilets, galleys and cargo-holds is not recirculated but instead is released directly overboard. The cabin air in a typical airliner aircraft such as an Airbus A320 is completely changed, on average, every three minutes, which compares to every 10-12 minutes in a typical air-conditioned building.

Can the SARS-Cov-2 virus be spread by recycled cabin air?

This is unlikely because air that enters the cabin and passes over the occupants is extracted at floor level and then either exits overboard via pressurisation outflow valves or passes through the HEPA filter prior to being mixed with fresh air and re-entering the cabin. For aircraft equipped with HEPA filters, European Union Aviation Safety Agency (EASA) operational advice is to promote increased fresh air flow through the continuous use of recirculation fans at high pack flow, whenever possible.

What about the use of face masks?

Wearing a face mask can potentially reduce the release of the virus through coughing and sneezing, and so could lessen the risk of exposure from infected persons. The World Health Organization (WHO) has recently amended its guidance and now advises governments to encourage the general public to wear masks in specific situations and settings.

EASA recommends that face masks should be worn at all times by crew members having direct contact with passengers or other individuals that are not part of the crew. As part of their recently published COVID-19 Aviation Health Safety Protocol, EASA also recommends their use by passengers and from 15th June it will be mandatory in the UK for passengers to wear face coverings on public transport (including aircraft).

What about physical distancing?

The size and layout of aircraft cabins create difficulties in achieving recognised social distancing criteria, and the consequences in terms of passenger loading could be economically unfeasible for airlines. However, with load factors currently at relatively low levels, the combination of physical spacing and use of face coverings/masks could give the public the confidence to travel. EASA recommends the use of physical distancing whenever feasible. Cabin crew could also manage passenger use of toilets to facilitate physical distancing and prevent queuing.

What other measures can be taken?

Ultimately, other than thorough and regular hand washing which applies at all times, the most desirable measures are those that reduce the likelihood of infected passengers boarding an aircraft in the first place.

An internationally coordinated, multi-layered approach as promoted by the International Civil Aviation Organization (ICAO) Public Health Corridor concept is the way forward. Measures include but are not limited to staying at home when not feeling well (or presenting with symptoms), temperature screening at airports (accepting that its value is maybe more a deterrent to travel than an effective identifier of those who are infected), social distancing (wherever possible), use of face masks/coverings and testing for COVID-19 (when this can be accomplished reliably, quickly and at high capacity, or if/when the science determines that immunity can be conferred for those who have had and recovered from the virus).

At the same time regular deep cleaning and disinfection of aircraft (as per EASA guidance) is essential. Aircraft operators are responsible for ensuring disinfection of aircraft at a frequency based on their usage and as recommended by the aviation regulators in coordination with the local public health authorities. Contact points in toilets should also be cleaned at regular intervals. Airlines can also minimise contact point opportunities (e.g. removal of physical inflight magazines and use contactless payment for onboard services if required).

Above all else, the most effective measure to limit the potential transmission of the virus is rigorous hand hygiene, so passengers should use hand sanitisation whilst onboard.

Overall, the perception that people travelling by aircraft are exposed to a high risk of becoming infected with coronavirus because of ‘stale air’, is not supported by evidence. Both the aircraft design and operational procedures help to ensure the risk is minimised. For every pilot, safety comes first and BALPA continues to work with the Government, regulators and airlines to ensure appropriate measures are put in place to protect passengers and crew from the risk of coronavirus when on board a flight.