What happened
On March 27, 2014, at 12:43 local time, a Swearingen Merlin III, registration N-125WG, operated by Medelair, and a Cessna 152, registration EC-JNL, operated by Aeroclub de Sevilla, experienced a near mid-air collision within the traffic circuit of Seville Airport.
The Swearingen Merlin III was conducting a private VFR flight from Muchamiel. Upon entering the control zone, the aircraft was flying at 1,500 ft and was instructed by the tower controller to descend to 1,000 ft and orbit at point N. Simultaneously, the Cessna 152 was performing local flight training maneuvers (take-offs and landings) on runway 27.
The tower controller informed the crew of the Cessna 152 of other VFR traffic orbiting in front of the tower and instructed them to orbit in the first third of the downwind leg of runway 27. However, the crew of the Cessna 152 provided an incorrect and incomplete readback, stating they would orbit north of the field. Consequently, the aircraft continued along the downwind leg toward the area where the Swearingen Merlin III was already orbiting.
At 12:43, the crew of the Cessna 152 spotted the Swearingen Merlin III and performed an evasive descent. The aircraft reached a minimum horizontal separation of 0.1 NM and a vertical separation of 200 ft. Shortly after, the crew of the Swearingen Merlin III reported that the aircraft had passed very close and warned that they were approaching the Cessna 15 and2 again due to the significant speed differential between the two aircraft (210 knots vs 90 knots).
The investigation
The CIAIAC investigation examined the radio communications, radar data, and the actions of both flight crews and the air traffic controller. The investigation established that the Swearingen Merlin III had entered the control zone at 1,500 ft without notifying its altitude. The investigation also reviewed the controller's instructions regarding traffic information and the accuracy of the readbacks provided by the flight crews.
Findings
- The primary cause was a defective readback by the Cessna 152 crew regarding the instruction to orbit in the first third of the downwind leg, which the controller failed to correct.
- The controller provided incomplete traffic information, which hindered the pilots' ability to locate the conflicting aircraft.
- The controller instructed the Cessna 152 to turn left, resulting in converging flight paths with the Swearingen Merlin III.
- The controller did not instruct the Swearingen Merlin III to return to point N to ensure separation until the crew themselves warned of a secondary collision risk.
Safety action
- REC 07/16: Recommended that the air traffic service provider, Ferronats, improve training for controllers regarding the provision of traffic information to VFR aircraft.
- REC 08/16: Recommended that Aeroclub de Sevilla implement measures to improve the ability of pilots and instructors to accurately follow and read back radio instructions.