HEPA air filtration seems to be one of the reasons that Covid-19 doesn’t appear to spread very much on planes. Big commercial aircraft refresh air inside the cabin with outside air frequently, perhaps 20 times an hour, and when air recirculates most of the virus gets caught in filters.
Many smaller planes, including 50 seat regional jets, do not usually have HEPA air filtration. That’s one reason why I’ve suggested staying away from small planes during the pandemic.
American Airlines Is Adding HEPA Filters To Small Regional Jets
Just as there’s been a huge move towards frequent cleaning of aircraft, there’s also been a push to improve air filtration, too. That’s important not just now but in the future too because HEPA filters can help reduce the spread of most airborne illnesses.
This month American Airlines’ wholly-owned regional carrier Piedmont took a big step, getting FAA approval to install HEPA air filtration in their 50 seat Embraer regional jet aircraft. The Supplemental Type Certificate, or ‘STC’, was approved October 6th and doesn’t even appear to be listed yet on the FAA website yet.
I spoke with Bill Arndt, Piedmont’s Vice President of Aircraft Maintenance and Engineering, about the project. He said that the thinking used to be that the ERJ-145 was designed “with so much fresh air coming in that they didn’t think needed filtration,” that they certainly viewed the aircraft as safe currently, but that they had already begun work on a project to do greater filtration prior to the pandemic so it made sense to fast track it now.
One major challenge is that HEPA filters are potentially flammable in the cabin. However they have the filters designed to be installed under the floor, out of the passenger cabin.
While they’re still in contract negotiations with local machine shops and welding facilities, most of the work to retrofit the planes with HEPA filters will be done in-house. They expect to have all of their 59 ERJ-145 aircraft upgraded by the end of the year. That’s faster than they anticipated being able to accomplish it – Arndt was amazed by how quickly the FAA moved on the certification.
Envoy Air, also fully owned by American Airlines Group and which used to be called American Eagle, has 80 ERJ-140 and -145 aircraft. Piedmont has given them the design and details on the project. American expects these planes will all be retrofitted with HEPA filters by March 2021. A spokesman for American tells me “so once the E140s and E145s are retrofitted with the new HEPA solution, our entire mainline and regional fleets will include HEPA filtration.”
I’ve written about the Covid projects undertaken by airlines that have seemed to be ahead of American (Delta especially). Given the relative importance of HEPA filters, compared to surface cleaning, this project has the potential to trump a lot of what other carriers have done so far.
How HEPA Filters Work
HEPA filters are essentially sheets of fiberglass fibers, with diameters between half a micrometer and 2 micrometers, randomly arranged. A fan pushes air through the filter, and particles get trapped inside. The very smallest of particles collide with molecules of gas, which slows them from passing through the filter and increases the chance of their becoming trapped.
HEPA filters aren’t really a kind of filter, though, the name speaks more to their standard of effectiveness – capturing at least 99.97% of airborne particles that are larger than 0.3 micrometers (or 0.00001 of an inch). Bacteria are easily trapped by HEPA filters. Viruses are smaller than a HEPA filter’s pores, but they often travel in clusters, on mucus, or respiratory droplets.
This level of air filtration was developed in the 1940s. The Manhattan Project used HEPA air filtration to limit the spread of radioactive material. They ‘spread’ into commercial use in the 1950s to catch viruses, pollen, bacteria, and other particles in the air.
Large commercial aircraft have these filters, and increasingly we’ll be seeing smaller ones have them too. That’s great news not just for travel now but also for those of us who are fearful of getting sick from our fellow passengers even during normal times.