FLYING Magazine
The FAA has proposed a new rule that would relax oxygen mask requirements for Part 135 and 91 operations, arguing that the changes would save operators millions of dollars annually without adversely affecting safety.
In a notice of proposed rulemaking (NPRM) published last week, the agency said the new rule would raise the altitudes at which at least one pilot at the controls must wear and use an oxygen mask during Part 135 commuter and on-demand operations. It would also permit Part 91 pilots of pressurized aircraft to fly at any certified altitude without a mask, if quick-donning masks are available. Comments on the proposal are due November 23.
The FAA defines a quick-donning mask as capable of being placed on the face with one hand within five seconds, without disturbing eyeglasses, delaying emergency duties, or disrupting normal communications.
The agency said its existing regulations are stricter than International Civil Aviation Organization (ICAO) standards. It said the rulemaking is justified due to improvements in pressurization and warning systems in modern aircraft, as well as the low rate of pressurization failures at high altitude. The agency reviewed over 20 million flight hours flown above FL250 by part 91 and part 135 operators and found only 200 instances of decompression events, with only a quarter of them above FL410.
According to the NPRM, the changes would reduce regulatory and economic burdens on Part 91 and Part 135 fleet operators to the tune of $4.7 million to $18.6 million annually for every 1 percent reduction in applicable servicing requirements. It estimated oxygen servicing costs are between $100 and $400 per fill.
Changes for Part 135 and Part 91
The proposed rule would raise the two-pilot quick-donning oxygen mask threshold under Part 135 from FL350 to FL410. It would also raise the single-pilot Part 135 mask threshold from FL 250 to FL350.
Section 834 of the FAA Reauthorization Act of 2024 directed the agency to consider whether to revise certain oxygen mask requirements for pilots aboard pressurized aircraft operating under Part 135 if the aircraft is flying below FL410.
Under existing Part 91, one pilot must wear and use an oxygen mask above FL350, but two-pilot crews equipped with quick-donning masks are exempt through FL410. The proposed rule would extend that exemption to all certified altitudes. Without quick-donning masks, at least one pilot must wear an oxygen mask above FL350, the same as the existing rule.
Justifications for the Changes
According to the FAA, since 1979, there have been 46 petitions for exemption from Part 135 oxygen mask rules, as well as six requests for relief from Part 91 rules requiring one pilot to wear and use an oxygen mask. The agency said it denied all of these “because the petitioners did not present safety mitigations unique to their operations.”
In 2021, for example, Merck petitioned for an exemption that would allow it to fly above FL410 without one pilot wearing an oxygen mask. It argued that design features of the Gulfstream G550/650 aircraft are designed to reduce the likelihood of decompression and provide for an automated emergency descent in the event of a decompression.
The National Business Aviation Association (NBAA) in support of Merck’s petition argued that wearing an oxygen mask decreases overall safety, due to modern aircraft design mitigations that make the requirement obsolete when quick-donning masks are available for two-pilot crews
The NBAA said Monday that it and other organizations “built the safety-data case that altitude-based mask thresholds set in the 1950s and 1960s don’t reflect modern aircraft design.”
“In the years following the exemption denials for both parts 91 and 135, FAA gathered and analyzed millions of hours of flight data at high altitude,” the agency said in the NPRM. “This information has significantly enhanced understanding of the effects and likelihood of decompression, crewmember best practices, improved design features, and common causes of decompression. Despite these advancements, current regulations have not been updated to reflect this new information and improved practices.”