Are planes safe during COVID?

Another great video, thank you. The COVID-19 pandemic has opened our eyes to many new and previously-underappreciated, important health-related matters. One of these is indoor air quality. As an HVAC system engineer, I have been astonished at the high percentage of HVAC systems that are poorly designed, poorly installed and/or poorly maintained. One or more of these deficiencies can easily result in poor air quality within a building. Such HVAC systems are highly prone to circulating air that transfers harmful fumes, particles, bacteria and viruses throughout all spaces being supplied. The HVAC systems in hospitals and "clean rooms" used in certain manufacturing facilities can be the exceptions since these spaces are highly sensitive to low quality air circulation. However, my experience has been that the vast majority of HVAC serving virtually every other industry have some degree of deficiency referenced earlier. There are local Codes and National standards that specify the design, installation and maintenance of HVAC systems, but in reality these standards are almost universally compromised for a wide range of reasons, with cost being at the top of the list. HVAC systems are generally invisible both physically and functionally to almost everyone, so there's a higher likelihood your local gym, restaurant, tavern or shopping mall has a system constantly introducing inadequately filtered air into the various spaces. I haven't addressed the residential HVAC situation which is far more susceptible to low indoor air quality than the commercial/industrial realms. My hope is that the current COVID-19 crisis will prioritize what most of us value, and that health-related matters such as HVAC systems will gain much more attention.