In the past when airlines struggled financially one of the first areas they cut back was cleaning, going over a year even without a deep clean. Despite Covid-19 being a bigger threat to airlines than 9/11 and the Great Recession combined, airlines have stepped up their cleaning to give passengers confidence to fly. It’s a welcome change that I hope continues even after the pandemic is done.

Different airlines have different strategies, from fogging or electrostatic spraying of disinfectant on planes, to United’s use of UVC light in its cockpits (but not passenger cabins), to American Airlines applying a chemical that will continue killing viruses long enough the airline has to spray planes only once a week compared to Delta disinfecting before each flight.

There have been concerns raised about the toxicity of some of the chemicals being used in passenger cabins, despite EPA assurances that they’re safe. Now the FAA though is weighing in with its own warning.

The FAA suggests that disinfectants being used could have a negative effect on aircraft interiors and urges airlines and maintenance organizations to “take extra steps to protect sensitive equipment, wiring, and other high-risk components.”

Their position is that just because the EPA says these disinfectants are safe for humans, and effective killing Covid-19, doesn’t mean they’re safe for aircraft use – though aircraft cleaning isn’t something that the FAA regulates (because it’s “not considered as maintenance under FAA regulations”).

Among the agency’s areas of concern: fogging and misting that allows disinfectant to penetrate areas where it could create problems, such as underlying structure or fan-cooled electronics. “Running aircraft ventilation will typically exacerbate this condition,” the bulletin said.

The FAA said it recommends electrostatic spraying over fogging, because sprayers offer more directional control. “[Using] either technique with the ventilation system off will reduce the risk of unintended application,” the bulletin said. “Note that airframe manufacturers continue to assess the implications of an operating ventilation system using specific disinfectants and may identify exceptions to this general advice.”

The FAA also advises increased inspections for corrosion in any areas where disinfectants are used.

Moreover the FAA worries about “[a]ny procedure that creates pools of liquid…[that] can intrude into flight deck switches and seals [and] lead to electrical shorts in the near term and unexpected corrosion in the long term.”

The FAA’s raison d’etre is caution. Giving hand sanitizer to passengers requires multiple levels of sign off at the FAA even though all passengers can bring sanitizer on board themselves and even though the the FAA studied on board sanitizer a decade ago and found it safe.

Nonetheless their concerns are ones already shared by airlines generally and there’s no actual real world examples of problems stemming from use of new disinfectants. Of course there are never real world examples until there are.