What happened
On 10 June 2013, a Xi’An MA60, registration PK-MZO, was operating a scheduled passenger flight from Bajawa Airport to El Tari Airport, Kupang. The flight, operated by PT. Merpati Nusantara Airlines, carried 46 passengers and 4 crew members.
During the approach, the aircraft's power levers transitioned into BETA mode at low altitudes. This change in engine configuration caused a significant increase in drag and a loss of lift, resulting in a hard touchdown approximately 58 meters from the start of runway 07. The impact was severe, with the Flight Data Recorder (FDR) recording a vertical deceleration of 5.99 G. The aircraft slid along the runway before coming to a halt. While the aircraft sustained substantial damage, the crew successfully evacuated the passengers through the rear main entrance. The incident resulted in five injuries, involving one crew member and four passengers.
The investigation
The investigation conducted by the NTSC focused on the mechanical state of the power levers and the procedural changes implemented by the operator. Investigators examined the aircraft's Flight Data Recorder, which revealed that the left power lever entered BETA mode at approximately 112 feet, followed by the right power lever at 90 feet.
Technical analysis centered on the Power Lever Lock mechanism and the electromagnetic stop. The investigation also scrutinized the operator's internal checklist revisions, specifically a requirement to keep the Power Lever Lock in the "OPEN" position during the approach phase. Furthermore, the investigators reviewed the Flight Crew Operation Manual (FCOM) for potential ambiguities in aviation terminology and assessed the operator's safety management processes regarding checklist modifications.
Findings
- The primary cause of the accident was the unintentional movement of the power levers into BETA mode, which induced high drag and reduced lift.
- The power levers entered BETA mode because the Power Lever Lock had been set to "OPEN" during the approach, a procedure introduced by the operator without a formal safety assessment or risk analysis.
- The pilot flying inadvertently moved the power lever stop slot, which facilitated the transition into BETA mode.
- The operator's approach checklist contained a non-standard instruction to keep the Power Lever Lock open, which was not present in the manufacturer's manual.
- Ambiguous aviation terminology within the FCOM contributed to potential misinterpretation of engine power settings.
- The operator's Master Minimum Equipment List (MMEL) lacked sufficient operational procedures to comply with local regulatory requirements regarding the Flight Idle electromagnetic stop system.