What happened
On September 14, 2013, at approximately 14:26 JST, a mid-air collision occurred at the Menuma Gliding Field in Kumagaya, Saitama Prefecture. The incident involved two privately owned gliders: a Rolladen-Schneider LS4-b, registered JA22WP, and an Alexander Schleicher ASK21, registered JA22RW.
At the time of the accident, the JA22WP was participating in a gliding competition and had just been launched from Gliding Field No. 1 via winch tow. Simultaneously, the JA22RW, used for flight training, was undergoing its own winch launch from the adjacent Gliding Field No. 2. As the JA22WP climbed, the pilot began a turn that took the aircraft diagonally across the airspace of the neighboring field. During this maneuver, the JA22WP made contact with the climbing JA22RW. The impact caused substantial damage to the JA22WP and minor damage to the JA22RW. Despite the collision, no injuries were reported among the pilot of the JA22WP or the instructor and trainee on board the JA22RW.
The investigation
The Japan Transport Safety Board (JTSB) examined GPS data from the JA22WP, interviewed the pilots and ground crew, and inspected the aircraft. The investigation focused on the flight paths of both gliders and the coordination between the two separate launch sites. Investigators analyzed the altitude and ground speed of both aircraft at the moment of impact, noting that the JA22WP was in a descending glide phase while the JA22RW was in a climbing phase. The investigation also reviewed the regulatory environment and standard operating procedures regarding the use of adjacent gliding fields.
Findings
- The collision occurred because the JA2 2WP flew through the airspace of Gliding Field No. 2 while the JA22RW was in its launch phase.
- The pilot of the JA22WP was preoccupied with finding a thermal to gain a competitive advantage, which led to a lack of situational awareness regarding the adjacent airfield.
- Neither pilot observed the other aircraft prior to the contact.
- There were no specific regulations or established standard practices requiring launched gliders to avoid the airspace of the adjacent field.
- The launch controller at the first field did not anticipate the aircraft would cross into the second field's airspace.