A continuance of carbon monoxide-related accidents and deaths has prompted the National Transportation Safety Board to make a second request to the Federal Aviation Administration to require carbon monoxide detectors in general aircraft.

The NTSB first made the recommendation in 2004, but the FAA’s response was to recommend general aviation and airplane owners and operators to install them on a voluntary basis. That apparently hasn’t been good enough.

A report by NTSB recorded 31 accidents between 1982 and 2020 tied to carbon monoxide poisoning.  Forty-two people were killed in 23 of those accidents and four more were seriously injured. Only one of the airplanes involved contained a carbon monoxide detector and it did not provide an audible or visual alert to the pilot as recommended by the NTSB.

“Carbon monoxide is dangerous for pilots and passengers alike — which is why the NTSB recommended that general aviation aircraft be equipped with carbon monoxide detectors in 2004,” Jennifer Homendy, Chair of the NTSB said in the release. “Once again, we’re asking the FAA to act before lives are lost to carbon monoxide poisoning.”

Carbon monoxide can escape undetected from defective mufflers, exhaust pipes, and other heat transfer systems, the report said. It’s colorless, odorless, and deadly. In 2004, the FAA also recommended regular inspections of exhaust systems and muffler replacements at specific intervals, but that hasn’t solved the problem.

The NTSB, according to the release, describes the FAA's current policies as “inadequate to protect pilots against the hazards of CO poisoning.” The agency also speculated that since toxicology testing for carbon monoxide can only be conducted on fatal accidents with suitable blood samples, “the actual number of accidents caused by CO poisoning may be higher,” the release said.