Merpati MA60 at Kupang on Jun 10th 2013, landed hard on runway and broke up

Indonesia's NTSC released their final report concluding the probable cause of the accident was:

- The procedure of selecting Power Lever Lock to “OPEN” during approach was made without comprehensive risk assessment.

- Both power levers entered BETA MODE at 90 feet due to the safety device namely Power Lever Lock has been opened during approach, which was in accordance to the operator procedure and lifting of Mechanical Power Lever Stop Slot which was not realized by the pilots.

- The movement of power levers to BETA MODE resulted the pitch angle changed to low pitch angle which produced significant drag and made the aircraft loss of significant lift.

The NTSC analysed that according to the FDR the propellers entered BETA mode at 90 feet AGL and remained in beta (reverse) producing substantial drag until after touchdown. The operator's procedures required the thrust lever locks, preventing the propellers to enter beta range/ground idle by limiting the thrust lever movement to flight idle, to be opened while on approach, the investigation did not find any safety analysis and risk assessment for this procedure change - the aircraft manufacturer's procedures do not contain the thrust lever locks to be opened on approach. Simulator tests verified that one both propellers went into beta range the aircraft descended rapidly, the NTSC stated: "The movement of power lever to ground idle will result to the propeller pitch angle changes to low pitch angle which produces significant drag. This drag will make the aircraft wing loss of significant lift."

The NTSC reported that the first officer had stated repeatedly during his post accident interview, that he had experienced delays when moving the thrust levers into ground idle after landing and stated: "This experience became his belief (cognitive)."

The NTSC continued: "In order to avoid delay on moving the power lever to Ground Idle during landing, the power lever stop slot should be operated immediately after landing. In this flight the SIC has operated the power lever stop slot during approach and unintentionally moved the power lever beyond flight idle (behavioral)."

The NTSC complained: "Several section of the FCOM contain of un-common aviation terminology such as Flight Idle (F.I) with additional information of minimum air power setting. F.I is a common terminology the additional information may result in different interpretation. So was Max Rev with additional information of setting of max antipull power."

The NTSC also analysed that the minimum equipment list requirements permitting the dispatch of the aircraft with the thrust lever lock inoperative as long as the lock was fixed in the open position was not in compliance with regulations "that no single failure (or reasonably likely combination of failures) or malfunction of the system will result in unwanted power lever movement toward BETA range and reverse under any expected operating condition."