What happened
On October 16, 2006, a Boeing 737-800 operating an IFR scheduled flight from Pisa, Italy, to Frankfurt-Hahn was on final approach to runway 21. Approximately two minutes before reaching the threshold, at a distance of roughly 7 NM, the aircraft's flight path was intersected by a Panavia Tornado flying under VFR.
The Tornado had departed Nörvenich military airfield for a training mission at the Baumholder range and was returning to base. During the return leg, the pilot of the Tornado descended from a cruising altitude of 6,000 ft, dropping below the altitude of the Boeing 737. The Tornado then performed a counter-clockwise circling maneuver while climbing through 4,300 ft.
As the aircrafts converged, the Boeing 737's Traffic Collision Avoidance System (TCAS) generated a climb instruction. The flight crew immediately complied with the resolution advisory, resulting in an aborted approach. After a subsequent approach was completed without further incident, the Boeing 737 landed safely at Frankfurt-Hahn.
The investigation
The BFU examined radar data from air traffic services and flight data from the Boeing 737's Quick Access Recorder (QAR), as well as excerpts from the Tornado's flight recorder. The investigation also reviewed radio communications between the Boeing 737 and Frankfurt-Hahn approach control, as well as the meteorological conditions at the time of the event.
Findings
- The minimum separation between the two aircraft was measured at 0.2 NM at an altitude of 4,300 ft.
- The unauthorized descent of the Tornado from 6,000 ft to a lower altitude placed it in the path of the arriving Boeing 737.
- Both aircraft were equipped with and operating functional transponders.
- The incident occurred in Class E airspace, where IFR flights are subject to separation, while VFR flights are responsible for their own separation from other aircraft, though they receive traffic information when possible.