What happened
On 22 November 2000, a Boeing 757-204, registration G-BYAN, operating a scheduled flight from Birmingham to Paphos, encountered a near-collision with a McDonnell Douglas F15E military jet. The incident occurred 5 miles west of the Daventry VOR within the Daventry Radar Corridor.
While the Boeing 757-204 was climbing through 10,000 feet in cloud, the crew was advised of military traffic 1,000 feet above. Although the crew attempted a visual search, the thick cloud prevented contact. Shortly after, the crew suddenly observed the McDonnell Douglas F15E passing at very close range at the same altitude. The aircraft passed across the nose of the Boeing 757-204, and the crew experienced the fighter's wake turbulence. Radar analysis later revealed the separation at the closest point of approach was less than 0.0625 nautical miles.
The investigation
The investigation examined the flight profiles of both aircraft and the air traffic control coordination. The two F15Es were flying in a 'trail' formation. The lead aircraft was transmitting a Secondary Surveillance Radar (SSR) code, but the second aircraft was not. The lead aircraft had been cleared to climb to 11,000 feet, but the second aircraft did not receive or act upon this clearance.
Investigators also reviewed the handovers between different air traffic control sectors. There was confusion regarding the number of aircraft in the military formation; a controller had mistakenly annotated a flight strip to indicate a single aircraft rather than a pair. Furthermore, the second F15E's radio transmission was partially obscured by a busy telephone line during a controller handover, preventing the controller from realizing a second aircraft was present.
Findings
- The primary cause was that the crew of the second F15E missed the climb clearance due to an inter-cockpit discussion.
- The second aircraft was not transmitting an SSR code, which rendered both the Short Term Conflict Alert (STCA) and the Airborne Collision Avoidance System (ACAS) ineffective as a safety net.
- The air traffic controller was unaware of the second aircraft's presence due to a combination of incorrect flight strip annotation and obscured radio communications.
- The second aircraft was operating in a 'stream' formation where it was not in visual contact with the leader, removing the visual backup for following ATC instructions.