What happened
On November 17, 2016, at approximately 12:38, a Remos GX ultralight aircraft, registration AJ2666, was performing touch-and-go training at the Jiao-Hao ultralight airfield in Pingtung County, Taiwan. The aircraft was operated by a flight school with an instructor and a student on board.
During the second touch-and-go of the flight session, the aircraft departed the runway and began a climb. While ascending, the aircraft's pitch increased significantly, causing the airspeed to decrease. During this phase, the aircraft experienced a sudden and severe left bank, with the bank angle exceeding 45 degrees. This maneuver led to a left slip and a subsequent loss of altitude. The aircraft's left wingtip and left main wheel struck the ground, causing the fuselage to slide and rotate 180 degrees before coming to a stop on the grass near the end of runway 26. The impact resulted in substantial damage to the aircraft and caused one serious injury and one minor injury among the occupants.
The investigation
The Taiwan Transportation Safety Board (TTSB) examined the aircraft's engine performance, flight data, and environmental conditions. Analysis of the engine monitoring system (EMS) showed that the Rotax 912 ULS engine was functioning normally, though the power output was approximately 10% lower than during the previous takeoff, suggesting the throttle may not have been at maximum position.
Flight data from the aircraft's electronic flight instrument system (EFIS) and GPS revealed that the aircraft's airspeed decreased as the pitch angle increased. The investigation also noted that the aircraft's left-turn tendency, a common characteristic of single-engine propeller aircraft during high-power, high-angle climbs, likely contributed to the sudden banking. While a small-scale dust devil was observed near the runway shortly after the accident, investigators determined it did not directly cause the crash.
Findings
- The primary cause of the accident was the reduction in the safety margin between airspeed and stall speed, driven by the student pilot's high-angle climb and insufficient airspeed.
- The aircraft's stability and controllability decreased due to increased wing loading during the steep climb.
- The aircraft was subject to a left-turn tendency caused by aerodynamic effects (torque, P-factor, and spiral slipstream) common in single-engine propeller aircraft during high-power, low-speed flight.
- The instructor failed to implement the correct stall recovery procedures and did not intervene early enough to prevent the aircraft from entering an unrecoverable state at a low altitude.
- The student pilot's high pitch angle during the climb led to a rapid decay in airspeed.