F-22 Raptors at the 1st Fighter Wing, Joint Base Langley-Eustis, Virginia, US, have been grounded again following an incident with one of the unit’s pilots, US Air Force (USAF) spokesman major Chad Steffey confirmed.

Defense News has reported officials as saying that the pilots were faced with an oxygen-related problem while flying the aircraft.

The grounding decision is limited to the Virginia USAF base.

The Raptor fleet resumed flight operations last month following a four-and-a-half month grounding after mitigating the risk factors associated with the aircraft’s oxygen system.

US Air Force spokesman Scott Knuteson said: "There is no conclusive cause or group of causes that has been established for the incidents that prompted the stand-down earlier this year."