What happened
On September 26, 2018, a Valentin Taifun 17EII motor glider, registered JA2451, departed Noto Airport for a pre-inspection test flight. During the initial climb, the aircraft encountered light turbulence, at which point the cockpit's radio and electrical instruments ceased functioning. The pilot reported smelling burning vinyl and observing thin white smoke emanating from the engine compartment.
Suspecting an engine fire, the pilot deactivated the ignition to shut down the engine and transitioned to a gliding flight. Due to the loss of electrical power, the pilot was unable to activate the electric propeller control to feather the blades, significantly increasing drag and reducing the glide ratio. Realizing the aircraft could not reach the runway against the prevailing headwinds, the pilot selected a grassy field approximately 3 km southwest of the airport for a forced landing.
After performing emergency manual gear extension, the pilot touched down on the damp, grassy terrain. While the landing was initially smooth, the aircraft's nose veered sharply to the left after rolling approximately 60 meters. The aircraft eventually came to a stop with the nose facing left, resulting in damage to the landing gear.
The investigation
The JTSB investigation focused on the electrical failure and the subsequent landing dynamics. Investigators examined the battery installation and the condition of the electrical wiring. They found that the starter/feeder cable was installed without the protective plastic covering typically used to prevent short circuits.
Furthermore, the investigation looked into the maintenance history, noting that a mechanic had recently removed the battery for a 100-hour inspection. The investigation also analyzed the landing site conditions, noting that the field was wet from previous rainfall, which likely contributed to the uneven braking forces during the rollout.
Findings
- The primary cause of the electrical failure was an electrical short circuit caused by the core wire of the feeder cable contacting the battery mounting bracket.
- This short circuit led to a large current flow through the return cable, causing it to melt and resulting in a total loss of electrical power.
- The pilot's decision to shut down the engine was prompted by the presence of fumes and smoke, which were byproducts of the electrical malfunction.
- The landing gear damage, including a deformed right main gear lock and a detached nose gear attachment, was caused by the aircraft veering left and experiencing asymmetric braking forces on the slippery, grassy surface.
Safety action
Following the incident, the Japan Aviation Academy implemented several preventive measures:
- Establishment of formal battery installation procedures that include protective coverings for feeder cables.
- Revision of preflight inspection protocols to require the opening of the engine upper cover to verify battery and wiring integrity.
- Update of periodic inspection checklists to specifically confirm the position of the battery mounting bracket and the condition of all electrical connections.