May 29, 2020, ©. Leeham News: In our Corner series about flying during the COVID-19 pandemic, we go deeper into the cabin airflow and procedures around the flight.
The riskiest phase of the flight is not when you sit down. The cabin airflow then transports the viruses away from your breathing. It’s the phases before and after the flight that are the danger zones.
The air conditioning system in an airliner, called the Environmental Control System (ECS), is designed to transport the exhaled air from passengers, and any germs it contains, away from the passenger breathing area.
To achieve this, it uses a downward flow (Figure 1), with air entering at the roof/bin level and exiting at the bottom of the sidewalls. It then returns in cargo-bay channels to the ECS mixing unit via hospital-grade HEPA filters that capture 99.9% of the germs, including the SARS-CoV-2 virus.
At the ECS mixing unit, re-circulating and outside air is mixed about 50:50 before re-entering the cabin at outlets in the roof and the overhead bins.
The downward flow in the seat rows is helped by the seatbacks, forming aerodynamic funnels, and the air in the cabin is exchanged 20 to 30 times an hour, an exchange rate that is to hospital standards.
Problem areas during the flight are movements in the aisle which will cause turbulence, thus potentially upsetting the orderly downward flow. This is why serving by the cabin crew will be minimized and passenger movements shall be restricted to lavatory visits.
Passengers fear the flight because they will be sitting next to strangers for a long time, with little control of the situation. Yet, this is probably the safest part of the whole trip.
For the airlines, the boarding and deboarding phase is the larger problem. At this phase, passengers easily end up face to face with minimal distances, Figure 2.
Airlines must introduce strict zone boarding to avoid such scenes, with the rear of the cabin and window seats boarding first, then the middle seats, and finally aisle seats. Then the next zone and so on.
Recent research points to SARS-CoV-2 spreading more over droplets than aerosols. This is why masks are so effective, as they stop the droplets in exhaled breathing air from reaching co-passengers, Figure 3.
So masks are essential in this phase, but they can easily dislocate while putting bags in the bins or making one’s way to a seat.
COVID-19 will require a new level of passenger discipline to manage all phases of flights safely.