What happened
On September 8, 2021, at approximately 12:19 JST, a close proximity event occurred near the west traffic pattern of Menuma Gliding Field in Saitable Prefecture. An Alexander Schleicher ASK21, registered JA2379, operated by Chuo University, was performing flight training following a winch launch. Simultaneously, a Cessna U206G, registered JA3904, operated by Suisan Aviation Co., Ltd., was conducting aerial photography near the area.
The pilot in command of the ASK21 was executing a turn from the crosswind leg to the downwind leg when the photography aircraft appeared at a 2 o'clock position. The glider pilot observed the U206G at a horizontal distance of roughly 100 meters and an altitude difference of approximately 50 to 60 meters. Due to the sudden appearance and perceived unpredictable movement of the other aircraft, the pilot of JA2379 took a preventive left turn to avoid a potential collision.
The pilot of the U206G noted the presence of the glider but continued on course, judging that the altitude difference was sufficient to avoid contact. As the U206G passed over the glider, the vertical separation was estimated by the photography crew to be between 90 and 120 meters.
The investigation
The Japan Transport Safety Board (JTSB) examined flight records, radar tracks from the Aeronautical En-route Information Service, and statements from the pilots and crew of both aircraft. The investigation focused on the communication attempts made by the photography aircraft and the operational status of the Menuma Flight Service at the time of the incident.
Investigators found that the pilot of JA3904 had attempted to contact Menuma Flight Service via VHF radio to announce the photography mission but received no response. It was determined that the Menuma Piste was being relocated due to an active runway change, which prevented the flight service from responding to the initial call.
Findings
- The primary cause was that the U206G entered the airspace over the gliding field and approached the ASK21 in close proximity.
- The pilot of JA3904 did not take evasive action, likely because they believed the altitude difference provided sufficient separation.
- The pilot of JA2379 performed a preventive maneuver rather than an emergency evasion, driven by the uncertainty of the other aircraft's path.
- Communication gaps played a significant role, as the flight service was unable to acknowledge the photography aircraft's presence due to the physical relocation of the radio station.
- There was no actual risk of collision or contact between the two aircraft at the time of the encounter.