What happened
On August 30, 2011, a Cessna C550B, operating flight NJE 262Q, departed Sion Airport on runway 25 following a high-performance instrument departure (IFR) toward Nice. Simultaneously, a Mudry Cap 10B, registration HB-SBE, was concluding an aerobatic training session in the vicinity.
As the Cessna C5/50B climbed, the Cap 10B began a descent to land. The pilot of the HB-SBE initially flew toward Martigny to lose altitude before turning left to join the runway's downwind leg. During this maneuver, the two aircraft's paths intersected. The crew of the Cessna C550B received a TCAS Resolution Advisory (RA) as the aircraft approached a dangerous proximity. Radar and TCAS data confirmed the closest lateral separation was only 0.5 NM at the same altitude, though the IFR aircraft was 500 feet above the VFR aircraft at the point of crossing.
The investigation
The Swiss Transportation Safety Investigation Board (SUST) examined radio communications, radar video recordings, TCAS data, and statements from the flight crews and air traffic controllers. The investigation focused on the coordination between the aerodrome control tower and the aircraft involved, as well as the adherence to local aerobatic flight procedures.
Findings
- The air traffic controller authorized the departure of the Cessna C550B without being aware of the exact position of the HB-SBE.
- The controller failed to provide traffic information to either aircraft.
- The crew of the HB-SBE did not monitor the tower frequency closely enough to note the recent departure of the IFR traffic.
- The flight path of the HB-SBE was more indirect than the controller had anticipated, as the pilot flew toward Martigny to lose altitude before turning back toward the airport.
- The failure to apply established procedures regarding the suspension of aerobatic activity when IFR traffic is prepared for departure was a primary contributing factor.
Safety action
- The investigation highlighted the necessity of strictly enforcing procedures that require aerobatic maneuvers to be interrupted when civil IFR aircraft are ready for takeoff.
- The findings emphasize the critical importance of delivering accurate traffic information to all aircraft operating within the CTR.