Earlier this month, a press briefing brought together three major aircraft manufacturers to talk about onboard transmission of COVID. Boeing, Embraer, and Airbus have all been undertaking in-depth studies of how viral particles move around aircraft cabins. Despite using different planes, methods, and tools, all arrived at the very same conclusion. Here’s what we found out.
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Airbus and the 3D modeling
The European planemaker’s research leaned heavily on software models for analysis. Using computational fluid dynamics, Airbus modeled how viral particles would travel in a cabin under normal airflow circumstances. With input from medical specialists from numerous countries, the model incorporated an accurate representation of passenger ‘emission events’, such as talking, coughing, sneezing or breathing.
The Airbus representative, Bruno Fargeon, explained the depth of calculation that went into the analysis, saying,
“The model is, in fact, a meshing of more than 50 million data points inside the cabin. And for each of these 50 million data points, we are computing the airspeed, the direction, the temperature … we repeat this calculation up to 1,000 times to represent one second in real time.
“It’s really a very intensive calculation.”
What they found was that, out of roughly 10,000 droplets expelled by someone coughing, barely any would reach a passenger sitting right next to the cougher. The larger droplets, it found, would immediately fall to the floor, while the smaller, aerosol particles would enter the airflow of the cabin, carried off to be either expelled from the aircraft or filtered out by the onboard HEPA devices.
Out of the 10,000 droplets, just five risked reaching the person in the adjacent seat. Consulting with medical professionals, who are still learning about the disease, the consensus is that there is an incredibly low risk of infection. However, the medical professionals could not guarantee that these five droplets would not be enough to cause infection.
Airbus moved to compare its findings with those of a real-world scenario to determine the risk to passengers. Airbus used the same tools and models to investigate the situation in a non-aircraft environment, such as an office, shops or other ground-based environments.
What they found was that, positioned six feet away from another person in a ground-based environment, which is the CDC recommendation of a social distance to minimize infection, 10 droplets would reach the person from a cough. This means that, onboard an aircraft with all the airflow benefits and natural barriers to transmission, passengers wearing a mask were at the same risk of infection as they would be when six feet from another person on the ground.
Testing with real planes at Boeing
Boeing’s research on aerosol transmission was similar to Airbus in that it focused on CFD and figuring out what the risk of droplets from passenger emissions reaching another passenger would be. Also similarly to Airbus, Boeing looked at the situation on a plane, and then compared it to different environments on the ground.
Initial studies noted that cough particles are distributed in a conical shape from a cougher. Heavy droplets would drop out of the path due to gravity, while others would avoid the breather as their trajectory would not allow them to come into the person’s breathing space.
Armed with this knowledge, Boeing sought to experiment with different airplanes to see how this played out in a real-world environment. The company conducted testing both on the ground and in-flight using the 737, 767 and 777. A device simulated a cough, releasing particles into the cabin air, and then sensors around the aircraft measured how many of those particles arrived in various locations.
As a comparison, similar tests were conducted in an indoor environment where there is little to no airflow, such as in a residential home. A third scenario looked at transmission in a conference room, where there would be standard building airflow, as is typically found in commercial buildings. In each environment, Boeing measured how many droplets arrived in other people’s breathing space at different distances from the cougher.
As with Airbus, Boeing realized it would be impossible to know exactly how many droplets it would take to make for an infectious dose, so rather than measure the number of droplets, the manufacturer sought to compare the distribution on an airplane with that of an on-ground scenario. Dan Freeman, chief engineer for Boeing’s Confident Travel Initiative, commented on the results, saying,
“What we found is that the number of particles and the breathing space compares to being greater than seven feet away, if a cougher is in an indoor environment in a stagnant airspace. We also found it to be greater than seven feet away in a building environment where there is some airflow involved.”
Freeman noted that Boeing is very confident that this is an accurate calculation of the transmission risk onboard and is further supported by the results Airbus got from its own testing. He concluded,
“Different tools, different assumptions, different airframe, different airflow, but very much the same conclusion.”
A full-size mockup for Embraer
Embraer too made use of CFD, but in tandem with a rather different testing environment. The manufacturer used a full-size mock-cabin, based on the popular E-Jet series, to test droplet dispersal over seven rows in the cabin.
For Embraer, the use of CFD has been common in aircraft production for many years, having used it to fine-tune airflow for air quality, noise reduction, and passenger comfort. This meant it came to the table with various models already formed but were keen to test out the computer-based modeling in a real-life scenario.
The mock cabin was equipped with a mannequin passenger, which simulated a cough through a mechanical device. Embraer measured particle dispersal using lasers to visually identify the trajectory of their movement. Air quality sensors were placed on seats around the cabin, which could measure particle distribution in different places around the cabin.
Slightly differently to Airbus and Boeing, Embraer considered the mass of the cough, which it measured as 200 micrograms. The results showed that, for passengers wearing masks, only 0.02% of the cough mass would reach the breathing zone, whereas, without a mask, it would be six times higher. Both were very small numbers and unlikely to be infectious doses but certainly validated the need to wear a mask onboard a plane.
Luis Carlos Affonso, Senior Vice-President of Engineering, Technology and Strategy for Embraer, commented on the findings, saying,
“Our message today is that because of the technology and procedures in place, you can fly safely – all the research demonstrates this. In fact, the cabin of a commercial aircraft is one of the safer spaces available anywhere during this pandemic.”
It’s fascinating to see three very different studies, using different methods and different planes, which all arrived at pretty much the same conclusion.
Does it make you feel more confident about getting on a plane to see the research that’s been done so far? Let us know what you think in the comments.
