What happened
On 17 April 2019, two Beech 200 aircraft, registered F-HCEV and F-HNAV, were conducting specialized calibration flights near Paris-Le Bourget. The crew of F-HCEV was tasked with calibrating the L’Aigle VOR radial, while the crew of F-HNAV was calibrating ILS systems at Paris-Charles de Gaulle.
During the flight, the crew of F-HCEV discovered that the radial they were intended to track actually passed through a prohibited airspace (P23) over Paris. To avoid this zone, the captain requested a heading change. The air traffic controller instructed the crew to visually track the Paris ring road. However, the crew' and the controller's interpretations of this instruction differed. The crew performed a left turn to join the radial, placing them on a convergent path with F-HNAV. This resulted in a first loss of separation, triggering a TCAS Resolution Advisory (RA) for both aircraft, with the horizontal separation dropping to 1.16 NM and vertical separation to 250 ft.
Shortly after, a second loss of separation occurred. The crew of F-HCEV attempted to follow the ring road but mistakenly identified a different motorway as the intended reference. This led them on a north-westerly track that again closed in on F-HNAV, resulting in a second loss of separation, though this time only a TCAS Traffic Advisory (TA) was triggered.
The investigation
The BEA investigation focused on why the aircraft deviated from their intended paths and why the separation was lost twice. Investigators examined the flight preparation, the accuracy of the published aeronautical charts, and the communication between the air traffic controllers and the flight crews. The investigation also reviewed the calibration system used on F-HCEV and the maintenance of the VOR station.
Findings
Several critical factors contributed to the incidents:
- Published Procedure Error: The published SID 21 contained an error; the radial to be tracked was actually radial 082, not 086. This error caused the intended path to pass through prohibited airspace.
- Inadequate Flight Preparation: The crew of F-HCEV did not verify the calibration engineer's manual plot against the FMS display, which would have revealed the discrepancy before takeoff.
- Visual Tracking Ambiguity: The air traffic controller's instruction to visually track the ring road was incompatible with IFR calibration flights. The crew's attempt to use a motorway as a visual reference led to the second conflict.
- Communication Breakdown: During the second phase, the crew of F-HCEV had doubts about their visual reference but did not communicate these concerns to the controller, and the controller did not seek clarification regarding the aircraft's unusual track.
- Maintenance Oversight: A previous finding that the VOR signal was unreachable at certain points had not been properly communicated to the relevant operations service, preventing a timely NOTAM from being issued to correct the procedure.