What happened
On July 25, 2012, at 12:10 local time, a near-collision occurred at Grenoble Isère airport involving two training aircraft. A Socata TB10 (registration F-GGNM) was returning from a local flight and was cleared by air traffic control to join the final approach for runway 09. The controller informed the crew that they were positioned behind a Piper PA2el in an IFR approach.
Simultaneously, a Socata TB20 (registration F-GGNQ) was positioned at the end of the downwind leg. The controller provided traffic information in English, instructing the Socata TB20 crew to follow the Socata TB10. The instructor in the Socata TB20 reported seeing traffic in the direction indicated and adjusted their circuit to follow the lead aircraft. Based on radio communications heard on the frequency, the instructor believed they were number two in the sequence, following the Socata TB10 and preceding another IFR aircraft located 4 NM away.
However, the aircraft the instructor actually identified as the lead was a Piper PA28 on short final. As the Socata TB10 continued its approach, the instructor noted the Socata TB20 passing slightly above and to the right at a higher speed, with an estimated separation of only 10 meters. The crew of the Socata TB10 immediately reported the near-collision to the controller. Following the controller's instruction, the crew of the Socata TB20 performed a go-around. There were no injuries and no damage to the aircraft.
The investigation
The investigation examined the air traffic controller's management of the sequence and the communication environment. The frequency was noted to be very busy with a high diversity of traffic, including both IFR and VFR instructional flights. The controller was assisted by a second controller responsible for coordination and supervision. The controller stated that while traffic was dense, they believed the aircraft were well-sequenced and that their strategy was to have VFR aircraft identify the preceding traffic to maintain separation without assigning specific sequence numbers.
Findings
- The primary cause was the incorrect identification of the preceding aircraft by the crew of the Socata TB20.
- Both crews failed to mutually detect the other aircraft during the approach.
- The controller did not assign a specific landing sequence number, which is standard procedure by the end of the downwind leg.
- The instructor of the Socata TB20 faced a high workload, as they were conducting flight instruction in English while monitoring a frequency where communications were primarily in French.
- The high volume of traffic on the frequency contributed to the difficulty in maintaining situational awareness.