Now that many airlines have relaunched flight operations, many of us are eager to fly again, but many of us also remain apprehensive about airborne disease transmission and we are not quite sure about what measures have been put into place to prevent infection in flight.   

In order to relieve some passenger worries and concerns, airline companies have been making statements and sharing information through social media about their constant disinfection of aircraft and that the HEPA filters within the HVAC systems prevent 99.97% of all bacteria and viruses. Therefore, by repeating that the risk of disease transmission on an aircraft is lower than in any given indoor environment, airlines have been trying to convince their passengers that the air within an aircraft is as clean as the air inside a surgery room.  

Scientists believe that the biggest problem in the spread of the virus is the density of the population in the aircraft as it essentially is a large number of passengers contained inside a relatively small area. At this point, more clean air support is required to maintain the air quality of the cabin. Experts agree that swift and frequent air cycles inside the cabin are essential. Experts also advise passengers not to switch off the individual air outlets called “gaspers” that are located on the overhead panel; while claiming that though it may not be the exact solution, it is one of the most effective alternatives available to prevent the spread of the disease.

IATA, Boeing and Airbus taking assertive action in communication 

“Guidance for Flight Operations During and Post Pandemic” published on June 12, 2020 by the IATA informs passengers on HEPA filters while it restores trust and reassures travelers. 

‘’HEPA filters have demonstrated good performance with particles of the size of the SARS-Cov-2 virus. Operators using the recirculation of cabin air are recommended to install and use HEPA filters, according to the manufacturer’s specifications. When HEPA filters are installed, recirculation fans should not be stopped during normal operations. The airflow induced by the cabin recirculation fans is designed to assist in maintaining the correct cabin airflow pattern.’’

The IATA also prepared and published the “Biosecurity for Air Transport” document on May 19, 2020, with the theme “A Roadmap to Restarting Aviation” also underlines that the analyses conducted have proved that the risk of catching COVID-19 from another passenger in an aircraft is quite low.

“Possible reasons are that customers sit facing forward and not toward each other, seat backs provide a barrier, the use of HEPA filters and the direction of the air flow on board (from ceiling to floor), and the limited movement onboard aircraft once seated add to the onboard protection.”

The U.S Manufacturer Boeing shares the view that they provide extremely purified air with the help of HEPA filters that have similar structures with the ones used in hospitals and industrial clean rooms. These filters are capable of filtering particles with over 99.97% efficiency and thus passengers could travel by Boeing aircraft without any hesitation. 

Moreover, by continuing its research studies on new technologies such as ultraviolet based disinfection systems and antimicrobial coating for frequently touched surfaces in the aircraft, Boeing has been seeking ways to minimize potential of infection transmission in the aircraft. The company has been working on activities towards increasing passenger awareness as well. 

Mike Delaney, working for Boeing for 31 years and now serving as the Vice President of Digital Transformation at Boeing Commercial Airplanes, has been appointed to lead the Confident Travel Initiative established to conduct all such activities. 

Airbus Engineering Head Jean-Brice Dumont also made statements, like the IATA and Boeing, assuring that passengers travelling by airplane are not exposed to any risks, and continued: “The air we breathe at any modern office is circulated nearly four times every hour, while in a modern aircraft the air is refreshed 20-30 times an hour. This, in the simplest terms, is the indicator of the importance we attach to the well-being of our passengers in flight, in addition to our commitment to their safety.” 

Both Airbus and Boeing say cabin air flows downwards not lengthways through the fuselage, reducing risks of infection. This vertical movement of air forms a protective barrier between rows, making it highly unlikely that the virus could pass between passengers seated in front or behind each other.

However, the actual case is not as simple as it may seem. The humidity of the air we breathe is very important and inside the cabin humidity is only 10% which leads to dry mucus in the throat and nose, and having this moist environment is part of the natural defense system of our body. Dry mucus in the throat and nose weakens our immune defense in a sense and creates an ideal environment for microorganisms to attack and spread infection. 

Boeing has another statement on this issue: “HEPA filters are not equipped to filter gaseous molecules. By increasing the humidity and adding new filtration technologies, studies show that the number of passengers experiencing the symptoms associated with dryness can be reduced, says a backgrounder on Boeing 787 Dreamliner.” 

How do HEPA filters work in an aircraft? 

We have been hearing a lot about HEPA filters recently.  Let’s take a closer look now at HEPA filters, which claim to be quite effective in avoiding the transfer of viruses between passengers in an aircraft.  

HEPA filters are composed of tightly knitted fibers used for the filtration of not only bacteria, viruses or harmful microorganisms but also many other types of contaminants such as dust, pollen or mold that may affect our health.

The word HEPA stands for ‘High Efficiency Particulate Air’ and HEPA filters are capable of removing all airborne particles of 0.3 microns in diameter and greater. 

HEPA filters started to be utilized in aircraft the 1980s and are presently available in all active aircraft of all airlines, since these companies have to build a certain level of air quality within the cabin due to international regulations. Thus, they endeavor to maintain this standard with HEPA filters.

The operation principle of the HEPA filter is as follows: There is a constant flow of air into the cabins during the cruise both for air conditioning and pressurization. The air outside is the main source of the air in the cabin with the required level of temperature and humidity. As a result of the conditions during the cruise of the aircraft, the extremely cold and low pressured air is mixed with air heated and pressured when passing through the compressors of the aircraft’s engines. Then, leaving the air mixing unit, the air starts to circulate within the cabin after being filtered through the HEPA filters. The average duration of the circulation is 3 minutes and part of the air in circulation is exhausted with the help of the outflow valves at the rear of the aircraft. The air remaining inside the cabin flows back to the air mixing unit. Here, the fresh, cold and low-pressure air is once again mixed with hot and high-pressure air that recently passed from the engines and it is circulated inside the cabin again. This same cycle is repeated every three minutes in flight.

Therefore, a portion of the air breathed in the cabin by passengers is left in the atmosphere and a major part of it is recirculated through the cabin as it is mixed with new, fresh airstreams. Scientists warn that the air breathed by passengers at any moment during the flight is always a mixed product. Then again, they also agree that as this circulation is frequently repeated, the air will become less harmful for the passenger as the former air can be diluted more rapidly.

The mixed air is purified through HEPA filters before it is circulated in the cabin again. We have already underlined that HEPA filters onboard airplanes are capable of filtering all particles that are 0.3 microns and greater in diameter. There have been discussions recently about a critical detail, it is a scientific question of whether or not the size of the diameter of the COVID-19 virus is smaller than 0.3 microns. The COVID-19 virus has been cited to be 0.12 microns. In this scenario, HEPA filters would fail to filter particles smaller than 0.3 microns, passengers would have to constantly breathe air contaminated by micro particles (virus or other contaminants) during the flight and this would cause a major risk. Surely, the discussions are still ongoing and there are no clear and generally agreed upon scientific publications in this area yet. The statements of esteemed organizations such as the IATA on one hand and the statements of aircraft manufacturers on the other have failed to fully eliminate passenger concerns in this respect. Objective, ethical, and scientific studies need to be conducted and published in this particular area in order to eliminate uncertainty and concern. However, it seems that we will have to wait for a while longer.

If we examine the existing process, we see that there are a just a few manufacturers of HEPA filters that are utilized in aircraft. Though each filter has its own rules of maintenance, all HEPA filters are replaced with new ones according to the maintenance lifecycle to ensure efficiency.

Even though airlines are deterring the spread of COVID-19 by using HEPA filters in their aircraft, we still should not overlook a certain fact. Some people might be under the impression that can only catch the virus through the air they breathe in, but we should not forget that the disease can also be spread by the surfaces we touch, potentially containing thousands of viruses or germs.

In conclusion, there are two main analyses on whether air travel constitute any risks to passenger well-being during COVID-19. The first one is whether air travel is safe for passengers or not. As I mentioned previously, the answer to this can be clarified with the help of conclusive scientific studies. The latter is slightly more complicated: Do passengers believe that air travel is safe? In order to remove this concern, airline companies and aircraft manufacturers may have to increase the amount they allocate toward this issue in their marketing budgets and thus ease the worries of their passengers