A Lakenheath-based fighter jet was involved in a near miss with a helicopter after accidently turning into a no-fly area.

The USAF F15 entered the Llanberis Pass, in Wales, in July and an RAF Griffin helicopter was forced to take 'immediate evasive action' to avoid the jet, according to a UK Airprox Board report.

The board said a navigation error led to the F15 inadvertently flying into the pass and the helicopter crew would not have been expecting the fast-moving aircraft to be in the vicinity due to flying restrictions.

The report said The UK Military Low Flying Handbook states that fixed wing aircraft should not enter the Llanberis Pass.

The report said: 'After reviewing flight data for [F15 C/S], it was determined that the pilot inadvertently turned north into Llanberis Pass.

'The pilot intended to fly north[wards] up the valley to the east [the Nant Ffrancon Pass], in accordance with local flying procedures.

'The pilot was thoroughly debriefed on the importance of maintaining positional awareness and flying in accordance with local established flying procedures to ensure de-confliction and maintain flow direction.

'It has long been recognized by the [48th] Wing that the Llanberis Pass is not to be entered by fixed wing aircraft.

'In this case, the crew mistook the Llanberis Pass for the adjacent Nant Ffrancon Pass.'

The RAF helicopter was on a mountain flying training exercise when the incident took place on July 5 this year.

The board did recommend that wording of flying regulations in the Snowdonia area should be reviewed to avoid confusion and changed from 'should not' to 'shall not enter the Llanberis Pass'.

The incident was given a category B risk rating, stated as 'Safety not assured: aircraft proximity in which the safety of the aircraft may have been compromised'.

Lt Elias Small, spokesman for the 48th Fighter Wing, said: 'Our pilots train every day to improve their skills, and they understand the importance of adhering to local UK flying procedures.

'Although the crew mistook the Llanberis Pass for the adjacent Nant Ffrancon Pass in this instance, we concur with the board's assessment that a review of the regulation will help reduce risk in the future.'