Two more Air Force 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 of 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. . .