Two more pilots were forced to land F-22s in recent weeks after experiencing symptoms of oxygen deficiency, two lawmakers said Tuesday.
The incidents led Rep. Adam Kinzinger, R-Ill., and Sen. Mark Warner, D-Va., to renew calls to the Air Force to pinpoint the cause problems that have plagued the service's stealth fighter for two years.
"I know the Air Force is trying, but we continue to not see the kind of definitive results that we are all hoping for," Warner said.
On July 6, an F-22 pilot at Joint Base Pearl Harbor-Hickam, Hawaii, declared an emergency and landed safely, just weeks after a similar incident at Joint Base Langley-Eustis, Va., the lawmakers said. Both pilots were flying without pressurized vests, the lawmakers said.
The pressurized vests emerged as a possible cause of the problems in early June, though Maj. Gen. Charles Lyon, director of operations for Air Combat Command, said at the time that the Air Force was not ready to declare victory. Pilots were directed, in most cases, to fly without the vest.
"We thought we were maybe on to something, but it appears there's more to be found, there's more to do," Kinzinger said Tuesday.
Air Force officials did not immediately respond to a request for comment.
Kinzinger and Warner sent a letter Tuesday to Air Force Secretary Michael Donley, outlining their concerns and asking for additional updates into the service's investigation. The letter requests an update within 30 days on all F-22 incidents, and requests more information on the investigation into the pressurized vests. The lawmakers also want details on a recent $19 million contract awarded to Lockheed Martin for the installation of an automatic backup oxygen supply system.
The Air Force plans to install the automatic backup system in F-22s later this year.
Last week, the Air Force announced that Gen. Mike Hostage, commander of Air Combat Command, had recently finished his qualification in the F-22, enabling him to fly the jet alongside other pilots while the investigation continues.
"As airmen, risk is part of our lives as members of the military," Hostage said in a release. "I'm asking these airmen to assume some risk that exceeds the norm in day-to-day training, and I have to be willing to do it myself and experience firsthand what they do."