What happened
On June 13, 2015, at 14:28 local time, a loss of separation occurred between three aircraft approximately 3.4 NM north of Puig, Valencia. The group involved included two Air Tractor AT802A amphibious aircraft, registrations Z3-BGU and Z3-BGV, operating in formation for a repositioning flight from Menorca to Valencia. Also involved was an AgustaWestland AW109E helicopter, registration EC-ILA, performing an emergency medical service flight.
The aircraft were flying in Class G uncontrolled airspace, where separation responsibility rests with the pilots. The two Air Tractors were flying at 1,300 ft, while the helicopter was at 1,000 ft. The aircraft were on convergent flight paths at similar speeds. During the encounter, the horizontal separation decreased to 0.3 NM, with a vertical separation of 300 ft. The pilot of the helicopter performed an evasive maneuver, descending to maintain separation. There were no injuries and no damage to any of the aircraft.
The investigation
The CIAIAC investigation examined the flight operations, air traffic control (ATC) communications, and radar monitoring capabilities within the Valencia TMA. The investigation noted that the Air Tractors were communicating with Valencia Tower, while the helicopter was attempting to contact Valencia TACC but was unable to do so due to a frequency change that had not been widely communicated.
Investigators found that the Air Tract and Tower controllers had incomplete information regarding the incoming traffic, receiving updates only three and a half minutes before the incident. Furthermore, a radar interpretation error occurred where the helicopter's radar echo was misidentified as a second aircraft within the Air Tractor formation. The investigation also highlighted that the Air Tractor formation was using a single flight plan and a single active transponder, which contributed to the difficulty in identifying the individual aircraft.
Findings
- The primary cause of the incident was a lack of communication and coordination between the aircraft, which allowed their convergent trajectories to continue until the conflict occurred.
- The helicopter was unable to establish contact with Valencia TACC because of an uncommunicated change in working frequencies.
- Air traffic controllers misidentified the helicopter as part of the Air Tractor formation due to radar interpretation errors.
- The disappearance of previous radar echoes for the Air Tractors was caused by a transponder code change during the flight.
- The AIP (Aeronautical Information Publication) for the Valencia TMA lacked specific instructions for VFR traffic to monitor certain frequencies, unlike similar procedures in the Barcelona or Palma TMAs.