4

Aircraft Design and Flight Operations, Personnel, and Performance

In the workshop’s third session, a panel of three speakers examined the changes that could be made to aircraft design and flight operations to limit the risk of viral transmission during air travel. A particular focus addressed passenger perceptions of the risks associated with domestic and international air travel for current and future pandemics. The topics of discussion included how changes in aircraft design could reduce the risk of disease transmission, the size of future aircraft in light of pandemic concerns, how the aircraft crew training might be modified in the future, and what changes should be made in the interactions among passengers and between passenger and air crew.

The first speaker was Howie Weiss, a professor of biology and mathematics at Pennsylvania State University and the co-principal investigator of the FlyHealthy research study. Next was Wolfgang Wohlers, vice president of engineering and maintenance at Airbus. The third speaker was Bob Fox of United Airlines and the Air Line Pilots Association International. After the presentations, the three speakers took part in a question-and-answer session moderated by workshop planning committee member Valerie Manning.

PREVENTING INFECTIOUS DISEASE TRANSMISSION DURING AIR TRAVEL

In the session’s first presentation, Weiss began by saying that there have been a number of documented cases of in-flight transmission of infectious diseases over the years. These diseases included COVID-19, sudden acute respiratory syndrome (SARS), influenza (including the 2009 pandemic of the H1N1p strain), tuberculosis, measles, norovirus, shigellosis, and cholera. In particular, he said, the transmission of COVID, SARS, and H1N1p show that air travel can serve as a conduit for the rapid spread of emerging infectious diseases and pandemics.

The FlyHealthy study, which Weiss directed along with Vicki Hertzberg of Emory University, was designed to look at the details of how a respiratory infection such as influenza is passed among passengers on an airplane. To date, there have been three peer-reviewed publications generated from the research carried out in that study. One of them examined the microbiome in an airplane cabin.¹ “In a nutshell,” Weiss said, “the airplane cabin microbiome looks like the microbiome of your conference room or classroom.”

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¹ H. Weiss, V.S. Hertzberg, C. Dupont, J.L. Espinoza, S. Levy, K. Nelson, S. Norris, and the FlyHealthy Research Team, 2019, The airplane cabin microbiome, Microbial Ecology 77(1):87–95.

The main study looked at the transmission of respiratory diseases, particularly influenza, during transcontinental flights.² Over the course of 10 flights across the United States, members of the research team carefully observed the movements of passengers and crew in the economy cabin of single-aisle aircraft. The team noted who came in close contact with whom throughout the flight. Using the movement data combined with an estimate of the respiratory disease transmissibility, the team developed realistic models of the transmission during the course of a flight. A key conclusion of that study, Weiss said, was that if one assumes that most direct transmission occurs within 1 meter, then there should be very few cases of transmission aboard an aircraft beyond transmission among nearest neighbors.

More generally, he said, the current understanding of how influenza, coronaviruses, and other respiratory viruses are transmitted in built environments with high air-exchange rate—for example, aircraft cabins during flight and hospitals—is that most direct transmission occurs within 1–2 meters of an infectious person. However, Weiss added, there are some data that suggest that this is not exactly the case. When he and Hertzberg examined reports of in-flight transmission of influenza and SARS, they found six studies that included seat maps of infectious persons. Those six studies reported 56 cases of disease transmission, and of those only 30 cases occurred for passengers sitting within two rows, or about 2 meters, of each other. The other 26 occurred when the separation was greater than two rows.³ “So we think,” he said, “this might call into question the current understanding of how, at least, flu and SARS might be transmitted.

Weiss said that he has spent a great deal of time in trying to understand a seating diagram for a Boeing 737-300 during a 3-hour flight from Hong Kong to Beijing that took place in 2003. A passenger seated in row 14 was infectious with SARS and died 2 days after the flight. Eighteen other passengers and two flight attendants were infected on that flight. What is confusing about it, he said, is that there were more passengers infected who sat more than two rows away from the index patient than who were sitting within two rows. There were more transmissions to passengers sitting on the opposite side of the cabin than on the same side as the index patient. “So, this is still quite a puzzle,” he said.

What then, he asked, can be done to prevent the transmission of respiratory infections during flight? In principle, passengers could all be required to wear N95 masks and eye protection for all flights. This would go a very long way toward preventing transmission, he said, but it would be impractical. Instead, a more practical and effective strategy would be to keep infected passengers off airplanes and, even better, to prevent them from entering very far into the terminal. How can this be achieved? The ideal approach places a biosensor at the security screening location. The sensor would sample exhaled air from every individual coming through and instantly screen for any respiratory diseases of concern. The problem with this approach is that a small sample of exhaled air from an infectious individual contains only tiny amounts of nucleic acid—not enough for detection with today’s instruments—so the nucleic acid would have to first be amplified. The standard way to amplify deoxyribonucleic acid (DNA) is with polymerase chain reaction (PCR), but it takes 45 minutes to an hour to complete that process. Furthermore, most pathogenic viruses, including COVID and influenza, are ribonucleic acid (RNA) viruses, so before the amplification step it would be necessary to transform the RNA into DNA using reverse transcription—a process that also takes about an hour to complete. This approach would obviously be too slow to be practical.

However, the COVID pandemic has sparked a huge amount of research into new detection techniques. For instance, there are new DNA amplification methods that are much faster and simpler than PCR. Additionally, the time required for the reverse transcription step has also been greatly reduced. Weiss described three such processes.

The first is the slowest one, he said, but it is actually in current use in hospitals and clinics. It is called loop-mediated isothermal amplification (LAMP).⁴ The original description of the technique was published in 2000, and it is currently being used by Abbott in its ID NOW system. Abbott claims that with a sample from a throat, nasal, or nasopharyngeal swab, it is possible to get COVID test results back within 13 minutes with a specificity

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² V.S. Hertzberg, H. Weiss, L. Elon, W. Si, S.L. Norris, and the FlyHealthy Research Team, 2018, Behaviors, movements, and transmission of droplet-mediated respiratory diseases during transcontinental airline flights, Proceedings of the National Academy of Sciences 115(14):3623–3627.

³ V.S. Hertzberg and H. Weiss, 2016, On the 2-row rule for infectious disease transmission on aircraft, Annals of Global Health 82(5):819–823.

⁴ T. Notomi, H. Okayama, H. Masubuchi, T. Yonekawa, K. Watanabe, N. Amino, and T. Hase, 2000, Loop-mediated isothermal amplification of DNA, Nucleic Acids Research 28(12):E63.

of 99 percent, and a sensitivity that has been measured at from 76 precent to 93 percent, depending on the study. Apparently, Weiss said, the test struggles with samples with a low viral load. However, assuming that the higher sensitivity is possible, sampling during security screening and quickly testing them could prevent most infectious passengers and crew members from boarding an aircraft.

The second technology is so recent, he said, that the only publication describing it was a 2020 preprint.⁵ The team combines the amplification and reverse transcriptions steps and greatly speeds up the reverse transcription. The group claims, Weiss said, that it can accurately identify viral RNA derived from COVID patient samples in less than 5 minutes. At this point, there is little more than a proof of concept, he said. Nonetheless, it is an exciting possibility.

The third technology is electrochemical impedance spectroscopy, a technique used since 2008 to detect the influenza virus. The idea behind it is to transform biochemical information from a specific molecular binding event—the binding between the spike protein on the coat of the COVID virus and angiotensin-converting enzyme 2 (ACE2)—into an easily measurable electrical signal. The authors of a recent study claim that they can detect the presence of COVID within 4 minutes from a nose or throat swab or saliva samples. The technique uses low-cost materials and has a greater than 85 percent sensitivity and greater than 85 percent specificity.⁶ Furthermore, the authors claim that the technique is scalable.

Weiss concluded with a few remarks. First, there are currently many other very rapid detection technologies under investigation; some use clustered regularly interspaced short palindromic repeats (CRISPR), and some use biosensors attached to the skin. Given this movement, he believes that within a few years it will likely be practical to screen passengers and crew for respiratory infectious diseases inexpensively and with high accuracy, with results available in less than 1 minute. Among the respiratory diseases of concern in airplane cabins are newly emerging strains of influenza and coronaviruses, tuberculosis (on international flights), and perhaps measles and bioterrorism agents.

Any screening technologies that are looking for highly conserved regions of a viral genome will be able to detect emerging strains; on the other hand, they will not be able to tell the difference between old and new strains. Last, if infectious passengers and crew members are detected and prevented from leaving the security area, then there will be little need for other measures such as changes to aircraft and terminal ventilation systems, modifications to terminal and aircraft seating, modified boarding procedures, health passports, and contact tracing. It would also limit how often flight crews must deal with uncooperative passengers, greatly assuage public concern about flying during outbreaks, and make it less important for researchers to determine routes by which COVID and other diseases are transmitted in terminals and on planes.

MINIMIZING RISK OF VIRAL TRANSMISSION

In the next presentation, Wohlers described a variety of ways in which aircraft design, operations, and personnel could be modified to make flying safer in the current and future pandemics.

Wohlers began with discussing the airflow in the cabin, and he suggested that aircraft manufacturers and airlines should keep rather than change current designs. While the airflow in today’s commercial airliners may not prevent all infection transmission, he said, it makes an airliner cabin a safer place than almost any other indoor environment. “This is something we should not change in the industry,” he said, “because this is giving us a good starting point.”

Moving on to suggested changes, Wohlers said the first thing to think about is how to design aircraft to help passengers limit their physical contact with the aircraft itself. He listed a number of possibilities. One was the development of touchless features (such as touchless faucets) and digital interactions to replace items that now require a physical touch. Passengers could also be encouraged to bring their own devices in order to avoid using the

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⁵ J.G. Carter, L.O. Iturbe, J.-L.H.A. Duprey, I.R. Carter, C.D. Southern, M. Rana, A. Bosworth, et al., 2020, Sub-5-minute detection of SARS-CoV-2 RNA using a reverse transcriptase-free exponential amplification reaction, RTF-EXPAR, medRxiv 2020,12.31.20248236.

⁶ M.D.T. Torres, W.R. de Araujo, L.F. de Lima, A.L. Ferreira, and C. de la Fuente-Nunez, 2021, Low-cost biosensor for rapid detection of SARS-CoV-2 at the point of care, Matter 4(7):2403–2416.

on-board devices. It is not possible for passengers to completely avoid touching the aircraft, he said, but designers should look for ways to minimize contact.

For those surfaces that will be touched by passengers, airlines should include cleaning and disinfection as part of the normal turnaround procedure, he said. There are limits, however, because airlines do not want to significantly increase turnaround times or the workload of the ground staff, both of which can affect an airline’s bottom line. An additional and complementary strategy would be the use of antimicrobial surfaces on aircraft where possible. Ultimately, Wohlers said, the answer is likely to be some combination of getting passengers to minimize their touching of surfaces, cleaning and disinfecting surfaces often, and using antimicrobial surfaces where feasible. Together with the cabin airflow, these features will provide an anti-transmission package that is more effective than what is being done today.

One possibility that airlines should look into, he said, is helping the cabin crew manage the passengers’ onboard movements. It is not possible to avoid passenger movement altogether—people must get on and off the plane, sometimes use the toilet during flight, and so on—but with things like disembarkation lights the crew can steer passengers more compared with pre-COVID habits. It will be important not to add too much to the responsibilities of the cabin crew, he said. The goal should be to get people on and off the plane more quickly and in a more orderly manner in order to limit interactions among the passengers.

Beyond the aircraft itself, Wohlers said that it is important to examine the entire air travel system—parking, transportation to and between terminals, movement within the terminals, security checkpoints, restaurants and shops within the airport, restrooms, boarding and deplaning, and time on the aircraft—for ways to minimize the risk of transmission. “From our point of view,” he said, “we do think that an end-to-end risk assessment model is key to assessing where to act.” If, for example, it is shown that terminals typically pose risks that are much higher than aircraft cabins, it does not make sense to focus mainly on reducing risk in the cabin. Making such comparisons requires the development of accurate models that can guide decisions concerning where to act and which means will be most effective in reducing risk, he said. The entire air travel industry is working on such models. Creating these models requires both good data and an understanding of the science behind the models, he said. Although each pandemic will be different, a good model could still help in anticipating how to counter future pandemics. This, he said, is a key thing for the airline industry to do. By anticipating and preparing for the next pandemic, hopefully the airline industry can avoid some of the worst effects of the COVID pandemic, such as the dramatic drop in the number of air travel passengers that occurred in 2020.

Wohlers’s final suggestion was related to the parking and storage of aircraft that are temporarily out of commission owing to the pandemic. Because airlines and aircraft manufacturers want the planes to be flying as much as possible, the procedures for parking and storage had not been a priority in the past. However, with the pandemic, Airbus ended up revising its manuals related to parking and storage, particularly the return-to-service procedures. There are probably also some design modifications that could be made to aircraft to help lower the costs related to parking and storage. The air travel industry as a whole should be thinking about the lessons learned from the pandemic about this aspect of operating aircraft, he said.

Closing on a personal note, Wohlers said that he had just finished a 3-hour flight during which he wore an FFP2 mask the entire time.⁷ It was not comfortable, he said, but it was “doable.” Ultimately, the key to safe air travel will be determining the most effective way to prevent infection and then putting that into effect, whether it is having passengers wear masks, cleaning surfaces after each flight, or something else. “We need to look at the overall assessment and the overall chain of events in order to avoid transmission as much as possible.”

A PILOT’S PERSPECTIVE

Fox began his remarks with a few details about the Air Line Pilots Association International (ALPA). ALPA represents 35 airlines in Canada and the United States and has about 60,000 members. In particular, ALPA represents not only large airlines such as Delta and United but also regional airlines. Fox said that the COVID pandemic has had a major impact on the regional airlines structure.

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⁷ A typical FFP2 mask looks the same as a typical N95 mask, but the former provides a lower level of filtration than the latter.

United Airlines, for example, has about six or seven regional partners that fly to smaller cities for United, he said. COVID showed that this regional model represents a weak point in the nation’s air travel system. After the pandemic hit, three strong regional airlines closed—ExpressJet, Compass Airlines, and Trans States Airlines—costing 3,500 pilots their jobs. There should be a better way of operating the nation’s air travel system, he said, one that offers more job security. He hopes that ALPA, airlines, manufacturers, regulators, labor unions, and other stakeholders can get together and solve the problem collectively.

Switching gears, Fox said that one of the clear lessons of the COVID pandemic is the importance of keeping air passengers safe. Historically, air travel has been the world’s safest mode of transportation. It is important to understand that this history of safety was accomplished through unions working with their companies and regulators to put in place a strong safety management system.

“What does that mean?” he asked. “That means that a pilot who sees a threat out there can voluntarily let everybody know, ‘hey, I see this threat,’ and the pilot doesn’t worry about being fired, not being paid for the month, or being disciplined.” That voluntary reporting system, combined with data drawn from computer systems on the aircraft, provides the data that Wohler, the prior speaker, had referred to as important to building models, Fox said. Eventually, such data played an important role in responding to the COVID pandemic. Initially, there were issues with consistency. Dozens of airlines were collecting data in real time, but they all had different policies in place. There was no universal guidance, for instance, on how to protect the health of airline crew and passengers. Different airlines were choosing different chemicals to wipe down surfaces and kill COVID viruses, sometimes with little knowledge about the effects those chemicals might have on the people applying them or the flight crew.

In response, ALPA called for the participation of an organization like RTCA, a nonprofit organization that develops technical guidance for aviation safety. Then, he said, the RTCA brought in 90 people from around the world to determine appropriate COVID-related standards for protecting the health of both airline passengers and crew. It was done quickly—within 100 days. It is vital, Fox said, that these standards stay in place after the pandemic in order to mitigate any similar, future threats.

Furthermore, he added, it is vital that similar standards be adopted by airlines throughout the world. The world’s air travel system is tightly interconnected, and problems that occur in one place can have repercussions elsewhere. This is a concern, he explained, because while there is an intense safety culture among airlines in North America and Europe, there is less commitment to safety elsewhere. As an example, he pointed to the crash of Lion Air Flight 610 in October 2018. The proximate cause was a safety system on the Boeing 737 MAX that mistakenly pushed the plane’s nose down and caused the aircraft to crash into the sea. Investigations showed that the same problem had occurred on that airplane on an earlier flight. The crew was able to maintain control of the plane, but they never declared an emergency. Because there was no safety management system in place for that airline, the pilots did not feel comfortable reporting what had occurred on that flight. As a result, standard maintenance was performed on the aircraft, and the next crew took over with no warning about the problems the plane was experiencing. That would have never happened with a North American airline, Fox said, because “any North American pilot would have declared an emergency and would have landed short based on the training they receive.” The issue would have been addressed before the plane was allowed back into the air.

Thus, one of ALPA’s goals, he said, is to examine the various standards and practices of airlines around the world and to see what can be done to raise those standards when necessary. In doing so, he said, it will be crucial that all the stakeholders are involved in the discussions, as that is the best way to make things better for everyone.

DISCUSSION

Manning opened the discussion period by commenting that when it comes to the COVID pandemic, companies such as Airbus, Boeing, and other manufacturers are not competing with each other. Instead, they are working together to exit the pandemic and get back to a more normal situation. Then, noting that Weiss had focused on transmission of the virus through the air while Wohlers had focused on surface transmission, she asked whether either had thought about how to best balance efforts focused on one versus the other.

Weiss answered that, as far as he knows, there is no definitive answer concerning how much viral transmission takes place through aerosols versus fomites (that is, surfaces)—for flu, for coronavirus, for anything. There

is no contradiction between working to prevent one route versus the other, he said. At this point, it is not clear which deserves more attention.

Next, Manning passed along a question from the audience about whether there are data concerning COVID infections among pilots and crew. Fox answered that because pilots and crew kept working through the pandemic—sometimes carrying passengers, sometimes carrying protective equipment and other cargo—that there were COVID cases. “We lost members,” he said. This makes it particularly important, he added, that the guidance that has been developed for COVID—such as the wearing of masks for pilots and cabin crew—should be maintained through the COVID pandemic and kept ready for the next. “This is not going to be the last threat of this nature on this continent,” he said. “We’re going to be dealing with this kind of thing in future.” So, given how important air travel is to commerce and the world economy, “we need to make sure that we have all these mitigating strategies in place.”

Andrew Lacher asked the panelists whether there were any specific procedures they recommend be adopted to control the movement of passengers during flight or during boarding and deplaning to minimize interactions. Wohlers answered that his group’s recommendation is to have a more guided and directed disembarking process, perhaps by using disembarkation lights. The goal is to prevent the chaos that often accompanies disembarking—with everyone standing up at once, jostling to get their luggage from the overhead compartments, and getting off the plane as quickly as possible. That brings passengers into contact with other passengers that they might not otherwise get too close to. Thus, having an orderly, row-by-row disembarkation allows people to maintain more distance from other passengers and minimize the risk of transmission.

Fox added that there has been a great deal of virus-related education aimed at airline passengers on such subjects as the importance of social distancing or washing one’s hands. It is important to build on this education, he said, “and not let it go away as we continue to move forward.” The more people understand the threat and how best to mitigate it, the safer everyone will be.

Manning next asked whether, given concerns about COVID exposure, it is safer to travel on a single long-haul flight or multiple shorter flights. That is, the question is comparing the hub-and-spoke system versus point-to-point flights. Wohlers said that modeling shows that the greatest risk to passengers of transmission is in the terminal. It is, therefore, best to minimize time in the terminal, which means that a single point-to-point flight would pose less risk than multiple connecting flights.

Weiss agreed with Wohlers that a single flight would pose less risk. Weiss then asked Wohlers what his models assumed about interactions among passengers and crew on the flights. In particular, Weiss referred to the research he had done with Vicki Hertzberg that mapped movements of passengers and interactions among passengers and crew on real flights. Did Wohlers’s models use such data to model in-cabin interactions? This is important, he said, because the models are likely to come up with different answers, based on what assumptions are made about passenger interactions. Wohlers answered that he is not an expert on modeling, but from what he understands, the Airbus model is based on the literature and statistics and not on actual measurements of passenger movements within an aircraft cabin. Then he offered to connect Weiss with someone at Airbus who would be more familiar with the modeling. The important thing is to keep the public flying safely, he said, so Airbus is happy to cooperate and share data with others.

Manning then passed along a question from Hertzberg, who said that one development of the pandemic has been “wastewater epidemiology”—essentially, monitoring wastewater from buildings to look for signs of COVID. Could that process, she asked, be applied to monitor aircraft wastewater or even cumulative samples of cabin air? Wohlers answered that it could be done with aircraft wastewater, but one would have to make sure the sample was from just a single aircraft, and this might not be practical to implement in an airport setting. As for cabin air, because the air is regularly vented to the outside of the plane and replaced with fresh air and because the air that is not vented is passed through HEPA filters, it would probably not be practical to monitor the air for viruses. Furthermore, while the filters would catch viral particles, they are not changed after each flight. It would be impossible to know which flight the virus found in a filter came from.

Workshop planning committee member Edward Crawley then directed a question to Weiss concerning the idea of testing passengers as they enter the airport. Given that there are likely to be false positives in any test, he said, this means that people will be kept from flying who are not actually infectious. On a 150-passenger flight,

for instance, a false positive rate of only 1 percent would mean that one or two healthy passengers would be turned away. Are airlines willing to accept the costs in customer relations and income from such a situation? Weiss said that his area is science, not policy, and that this is a question better directed toward airlines. He acknowledged that no test is perfect, but he suggested that there are strategies that could be used to deal with this issue. Perhaps, for instance, such testing could be done during a major outbreak but not after the outbreak. Perhaps it could be combined with other remediation strategies such as pre-testing and mask wearing.

Wohlers then responded to that question with “a view from the other side of the Atlantic.” He had flown that morning, he said, and everyone on the flight had to take an antigen test. They had to get a negative result in order to board or even to stay in the airport. However, he continued, this is not a policy of a single airline—it is a government policy in place across Europe. This leads to more acceptance than if it were an airline policy, he said. It minimizes the chances that passengers will blame the airline if they cannot fly.

Manning next posed an audience question concerning whether there is sufficient transparency in the collection and analysis of data. What can be done to increase public confidence that the risk of infection is as low as some in the aviation community say it is? Wohlers answered that companies need to be clear and honest about what their investigations find and what their limitations are. However, that transparency is not enough. Repetition is also important. “It’s not sufficient to just say, well, we disinfected the cabin,” he said. People need to see that the cabin is cleaned regularly—that it is not just an infrequent thing. Similarly, while it is important that companies be clear in their communications, it is equally important that they repeat those communications regularly. Otherwise, their efforts will not be effective. In short, companies need to be transparent, consistent in their communications, and clear on the limits of what they know, he said, “and then let people make their own educated choices.”

Fox said that pilots also play a role. Because of their strong reporting culture, pilots represent the last line of defense. If something is not being done correctly—particularly something that can affect the safety of the passengers and crew—pilots report it to the proper government officials to ensure that correct procedures are followed. Thus, passengers can be certain that no matter whether they are flying on major carriers or small regional airlines, the correct procedures are being followed to protect their health.

Hertzberg then asked the panelists about deplaning. Anecdotally, she said, she has heard from people who fly that even though the cabin crew announces that passengers will deplane row by row, people still tend to get up all at once and crowd into the aisle. So, she asked, is there any sort of socialization that could be used to minimize this kind of behavior? Fox answered that with 200 people on an airplane, it is unlikely that it will ever be possible to completely avoid bad behavior. The best approach, he said, will be to start by determining what the science says about whether certain deplaning approaches are safer than others. Then, if there is a clear safety benefit to a particular deplaning method, that method should be mandated by the regulators. Such an evidence-backed mandate will be the only way to get close to complete compliance. This mandate will also take some pressure off members of the cabin crew, who often get pushback when they try to enforce the rules of particular airlines.

Manning passed along another question from the audience related to cabin air flow while the plane is grounded. Wohlers answered that the flow is less guided and controlled during ground time because people are moving around and disturbing the flow. Furthermore, while an airliner in flight is constantly bringing in fresh air from the outside to mix with the cabin air, this is not done on the ground. The air ventilation and circulation on the ground is inevitably different from in the air.

Another audience question asked whether airliner manufacturers are considering designs that would make cabin transmission of airborne diseases less likely. Wohlers said that until March 2020, the manufacturers did not think about optimizing their aircraft with respect to pandemics. This is something that is still relatively new. Furthermore, he said, the traditional “tube and wing” design for aircraft is not really a poor design in terms of disease transmission because of the intense air flow in the cabin. It is probably not an optimal design, he said, but it is not bad.

As a final question, Manning asked which current COVID-related practices might be continued indefinitely in the future as new best practices are brought in to limit disease transmission. Weiss answered that in the future he will always have a N95 mask with him when he travels on a plane. If a passenger anywhere near him seems ill, he will put his mask on for the flight and be careful about disinfecting his hands. “I think that’s a simple, very inexpensive way of dealing with sick passengers in the future,” he said. Wohlers added that he would like to see

the more disciplined deplaning process maintained in the future—not so much to limit the risks of transmission but just because it is so much less stressful to deplane in this way. Fox said that aircraft have never been cleaner than they are right now, and that is something he would like to see maintained in the future. “It’s just going to be better for the health of not only our crews but our passengers as well,” he said.