What happened
On 12 March 2011, a Cessna 172 aircraft, registered PK-HAI, was performing a cross-country training flight from Cakrabhuwana Airport in Cirebon, West Java. The flight crew included a pilot instructor, two student pilots, and a mechanic helper.
During the takeoff roll on runway 04, the aircraft began to veer to the left approximately 235 meters from the start of the runway. As the aircraft reached a speed of 60 knots, the student pilot applied back pressure on the control yoke to pitch the nose up and correct the heading. However, because the instructor's seat was not properly secured, the seat began to slide backward. In an instinctive attempt to stabilize himself, the instructor reached for the control yoke, while simultaneously, the student pilot pushed the yoke forward to lower the nose.
These conflicting inputs caused the aircraft's pitch to increase sharply, triggering the stall warning horn and causing the lower rudder to strike the runway surface. The aircraft veered to the right, exited the runway, bounced twice, and eventually came to a stop after impacting a cliff. There were no injuries to the four occupants.
The investigation
Investigators examined the wreckage and the aircraft's control systems to determine the cause of the loss of control. The examination of the left control yoke revealed that the shaft had suffered an overstress failure at the pin hole due to sudden bending forces. Additionally, investigators found that the instructor's seat locking pin had not been correctly engaged in the seat track. The damage to the aircraft included a bent propeller blade, a broken windshield, a shifted engine mount, and the detachment of the nose landing gear.
Findings
- The primary cause of the loss of control was the movement of the instructor's seat, which led to uncoordinated and conflicting control inputs between the instructor and the student pilot.
- The instructor's seat had not been properly secured in its track prior to takeoff.
- The sudden, opposing forces applied to the control column resulted in the structural failure of the left yoke shaft.