What happened
On August 25, 2015, a privately owned Diamond Aircraft HK36TTC, registered JA21DA, was conducting a familiarization flight at Biei Gliding Field in Hokkaido, Japan. The pilot had previously flown to Takikawa Sky Park but returned to Biei after finding insufficient thermal activity for soaring.
During the return, the pilot decided to perform an engine-off landing as a training exercise, transitioning the motor glider into glider mode approximately 7 nautical miles west-northwest of the field. While approaching Runway 31, the aircraft was at a lower altitude than the pilot's standard approach profile. To align with the runway, the pilot executed a left turn with a bank angle of 35 degrees, which was steeper than the typical 25-degree bank used for this area.
During this maneuver, the aircraft's left wing tip struck the ground on the grassy area north of the runway. The impact caused the aircraft to tilt, leading to the failure of the nose landing gear and the horizontal stabilizer. The aircraft eventually came to a stop approximately 35 meters from the runway.
The investigation
The Japan Transport Safety Board (JTSB) examined the flight history, weather conditions, and the physical state of the aircraft. Investigators noted that the weather was clear with light winds. The investigation focused on the pilot's decision-making process regarding the approach altitude and the steepness of the turn, as well as the mechanical consequences of the wing tip striking the terrain.
Findings
- The aircraft was flying at a lower altitude than usual when approximately 1 nautical mile from the field, making it difficult to maintain the standard approach path.
- The pilot utilized a steeper bank angle than normal, which likely led to a loss of flight control balance and a steeper-than-intended descent.
- The pilot's persistence in attempting a specific landing area on Runway 31 prevented a safer decision-making process.
- Had the pilot opted to switch to Runway 13 or restart the engine to regain altitude, a safe landing could likely have been achieved.