After a two-month hiatus, one-third of the scheduled domestic flights will resume operations from May 25. The civil aviation ministry said all passengers will have to provide their medical details through the Aarogya Setu app or by filling up a self-declaration form, while those residing in containment zones will not be allowed to travel.
The resumption of domestic flights, however, has raised concerns about health and hygiene as the government has admitted that one-meter social distancing norm is not viable inside the aircraft.
But aviation experts say that even if social distancing is exempted inside the aircraft, flying is still the safest option among all modes of travel. According to experts, after the outbreak of Severe Acute Respiratory Syndrome (SARS), a viral respiratory illness first reported in 2003, the aircraft manufacturers have been upgrading the cabin air system substantially.
Technical experts say that the cabin has multiple highly efficient airflow and filtration systems to ensure that air remains clean all the time. While the airflow goes from right-to-left or front-to-back in a normal air-conditioning, in the aircraft, the airflow is downward at the rate of one meter per second. Aircraft manufacturers say that this minimises the risk of cross-contamination.
Experts also claim that cabin air is fully filtered and renewed every two to three minutes.
Krittivas Mukherjee, an aviation professional, said in a tweet, “At 10,000m cruise altitude, the air is very dry, very cold (-50 degrees) but the air is controlled (temperature, pressure, oxygen & humidity) before being injected back into the cabin.”
“Air is sucked out through vents on the floor & transported through highly efficient HEPA filters that flush out 99.95% to 99.97% of particles, including (relatively big) Coronavirus,” Mukherjee tweeted further.
The COVID-19 virus is approx. 0.125 microns (125 nanometers) in diameter. Aircraft manufacturers claim that the particle-size range that HEPA filters capture is 0.01 micron (10 nm) and above.
“Most of us think filters work like nets, they don’t. Particles, as small as the SARS-COV2 virus, get captured using a mechanism called “diffusional interception. The cabin air system delivers roughly 50% outside air and 50% filtered recirculated air,” a technical expert says.
Experts dealing with air-filtration systems say that because of all these measures, the air in the cabin is very clean, comparable with that of the best of hospitals.
Further, while rail and car travel can take 10 times longer than a flight to a far-off destination, overall exposure in a closed environment such as in an aircraft is much less.
Rajeev Ranjan, a doctor at Lab Medicine in AIIMS, Delhi, says, “I don’t know about how air filtration works in an aircraft, but I can say for sure that the duration of exposure is vital for contracting the viral infection and increasing its load in the body. If you are in a closed and clean environment for a shorter period of time, there is less possibility for you to contract the virus."
According to technical experts, there is a significant difference between the air quality when the door is closed before a flight takes off and the cabin air after the flight take off.
“This is because of the complete air-ventilation system in an aircraft. It ensures that the air inside is always of better quality,” a technical expert says.
Sanath Kaul, an aviation expert and a former joint secretary in the Ministry of Civil Aviation, says, “I have also heard about the technical aspects of the air-cleaning system and I have no reason to disbelieve it. It is modern and works better than the air-conditioning system in trains and metros.”
Having said that, aviation professionals say that besides various in-built protocols to keep air quality clean, it is necessary to take other precautions such as wearing a mask, sanitising hands and disinfecting surfaces and cabins frequently.