ANCHORAGE, Alaska — The Air Force says a landing gear malfunction likely was the cause of an emergency landing of an F-22 Raptor fighter jet in Alaska, that resulted in the aircraft leaning on its left side.

The F-22 made the landing early Wednesday afternoon at Joint Base Elmendorf-Richardson in Anchorage.

The pilot was not injured.

Air Force spokeswoman Erin Eaton says the base launched in investigation after the emergency landing. A preliminary review pointed to the landing gear problem, the Air Force said in an announcement Thursday afternoon.

The F-22 is a twin-engine, single-seat fighter produced by Lockheed Martin.

Two Raptors were scrambled last month to intercept and monitor Russian bombers in international air space west of mainland Alaska.