The U.S. Air Force is inspecting the emergency oxygen system on its F-22 Raptor air-superiority fighters.
AN F-22 RAPTOR awaits release from a hangar at Holloman Air Force Base, N.M., in September. (Senior Airman DeAndre Curtiss / U.S. Air Force)
Colloquially referred to as the "green apple" by pilots, the system is a self-contained supply of liquid oxygen mounted on the jet's ejection seat and is used in case there is a failure of the main life-support system. By necessity, it is separate from the aircraft's main oxygen systems, which have been under investigation for much of the year due to a string of airborne incidents where pilots have experienced symptoms resembling hypoxia.
"The Air Force is implementing an immediate action time compliance technical order (TCTO) on the F-22 backup oxygen system," a Dec. 8 Air Combat Command (ACC) release said. "This system is known as the Emergency Oxygen System (EOS) and is designed to be used on rare occasions when pilots experience indications or physiological symptoms that suggest there may be a problem with their air supply."
Air Force spokesman Scott Knuteson said that since the Raptor fleet returned to the air in September after a four-month grounding, pilots has been using the backup system more often than usual.
"We have adapted procedures to use the EOS as a precautionary measure to further protect pilots when they receive indications that physiological incidents may occur," the release reads.
However, even then the emergency oxygen system has not been used that often since the jets started flying again, Knuteson said. The pilots only use the system if a problem is detected, he said.
"We have used the EOS on less than one percent of the flights since we returned to flying status and experienced performance anomalies on a small number of EOS activations," the ACC statement reads. "These anomalies have been analyzed by technicians, and corrective measures have been validated and verified."
The inspection was ordered "simply as a prudent step to ensure the full functionality of the EOS given increased usage under current operating procedures," the ACC statement reads.
"As of Dec. 7, approximately 85 percent of the F-22s' EOS bottles had been inspected," Knuteson said. "The main focus of the TCTO is inspecting the EOS bottles and returning them to service."
In the meantime, Lockheed Martin is still delivering new Raptors to the Air Force. One of the newest jets was supposed to arrive at Langley on Dec. 8, but was delayed and will now arrive next week, said Lockheed Martin spokeswoman Alison Orne.
The service currently has 175 Raptors. Of the remaining aircraft to be delivered to the service, tail numbers 4186, 4187, 4189, 4191, 4192 and 4194 will be delivered to Joint Base Langley-Eustis, Va., tail 4188 will be delivered to Nellis Air Force Base in Nevada, while tails 4190, 4193 and 4195 - the last Raptor to be built - will be delivered to Joint Base Elmendorf-Richardson in Alaska.