Indonesia's National Transportation Safety Committee (NTSC) has issued a preliminary report into a hard landing at Kupang's El Tari airport that severely damaged a Merpati Nusantara Airlines Xian MA60 turboprop on 10 June.
The report suggests that the safety watchdog is focusing its investigation on an apparent discrepancy between the manufacturer's flight crew operations manual (FCOM) and the carrier's approach checklist. This discrepancy may have led to the left power lever being placed in beta range, thus generating significant drag, when the aircraft was at an altitude of 112ft (34m) on final approach.
"The flight data recorder [FDR] recorded that the left power lever was in the range of beta mode approximately 112ft and continued until touchdown," says the NTSC.
As a result of the crash, the NTSC grounded Merpati's 13 MA60s.
The preliminary report dictates that Merpati, Indonesia's only MA60 operator, take several actions. These include the suspension of first officer training until an internal investigation has been completed, follow-up training of existing MA60 pilots, and specific training focused on "hard/bounce landing recovery".
It has also recommended Merpati to review its approach check list, namely the item that pertains to the power lever lock system, and emphasise the performance of stabilised approaches.
The discrepancy between the FCOM and approach checklist specifically applies to an "electric magnetic stopping lock" that regulates movements of the aircraft's power levers. The FCOM suggests that the lock is to remain closed until landing, but Merpati's checklist calls for it to be opened during approach.
According to the NTSC's review of the MA60's FCOM, the document calls for the flightcrew to pull the power lever, which regulates the pitch of the propellers, to the "flight idle" position when on final approach. The lock apparently prevents the levers from being moved below "flight idle" and into the beta range, where "significant" drag will be generated.
After landing, the lock opens and the pilot can move the power lever to any position below "flight idle".
The report notes that the crashed aircraft's magnetic stopping lock was found in the "open" position. Opening the lock is consistent with the company's approach check list, but is not found in AVIC's FCOM. The "open lock" item was added in the carrier's 11th revision of the checklist dated 15 April 2012.
The NTSC adds that the MA60 cockpit has no visual or auditory indicator to show when lock is opened.
The aircraft - with registration PK-MZO - was operating as MZ6517 on the Bajawa-Kupang route, carrying 46 passengers and four crew members, when the accident happened at 09:40 local time on 10 June. Four passengers and the pilot suffered injuries. There were no fatalities.
El Tari airport serves Kupang, a town on the island of Timor.
The turboprop suffered severe damage in the accident, with the wing box partially detached from the fuselage, and the fuselage itself torn in the half forward of the wings. The wings were angled sharply forward, with the aircraft's left and right propeller hubs resting on the runway. Both engines lost all four propeller blades.
The report suggests that the co-pilot was flying the aircraft at the time of the crash, with the pilot monitoring the landing. The 42-year-old Indonesian pilot had total flight time of 12,530h, with 2,050h on the MA60. The 25-year-old Malaysian co-pilot had total flight time of 311h, with 141h on the MA60.
Flightglobal's Ascend Online Fleets database shows that the airframe was built in 2008, and delivered in December 2010. It bears the serial number MSN 0608.