Description

Two USAF-operated McDonnell Douglas F15E fighter aircraft declared as operating as a formation were pulling up from low level after encountering potential delays at their intended post-exercise destination due to deteriorating weather in preparation for a diversion. Despite being cleared to FL150 only, both continued to climb and both passed through the level of an Embraer 145 being operated by British Airways Regional on a scheduled passenger flight from Birmingham to Hannover, one seen at an estimated range of 100 feet. The aircraft were on different ATC control frequencies, being Operational Air Traffic (OAT) and General Air Traffic (GAT) respectively.

Investigation

An Investigation into this event was carried out by the UK AAIB because it was assessed as too dangerous to be handled by the UK AIRPROX Board which routinely deals with routine losses of separation.

The Investigation found that the infringement of controlled airspace by the two USAF aircraft had followed a level bust through their cleared level of FL150 and that Mode ’C’ altitude returns from both aircraft temporarily disappeared during the 1 minute 21 seconds they were passing through the airway. Visual contact with the civil aircraft was admitted by the F15 involved on their military ATC frequency with an apology.

It was found that "despite replying to the transmission correcting their cleared level to FL150, by the time the aircraft were handed over to London Military Tahoe 52 was already passing FL160 in the climb and both aircraft continued until level at FL230, suggesting the clearance was either misunderstood or ignored."