On 2 August 2009 a DHC-6 being operated by Merpati Nusantara Airlines on a scheduled domestic passenger flight from Sentani to Oksibil in West Papua in daylight and on a Visual Flight Rules (VFR) Flight Plan was in collision with terrain 6nm from destination resulting in the destruction of the aircraft and the death of all 15 occupants.
An Investigation into the accident was carried out by the Indonesian National Transportation Safety Committee. It was noted that the aircraft commander had been PF for the accident flight and that present weather reports relevant to the route and destination had not been available.
The aircraft involved was not fitted, nor was it required to be fitted, with an Flight Data Recorder (FDR) but the required and fitted Cockpit Voice Recorder (CVR) was recovered from the crash site which was at an altitude of 9,300 feet. Disposition of the wreckage indicated that the aircraft had been in a left turn at impact. The last reported stated altitude had been 9,500ft and a climb had apparently been intended.
It was noted that there were no ground-based navigation aids along the planned route or at destination but that the aircraft had been fitted with a Global Positioning System (GPS) receiver. It was also noted that the operator supplied flight crews with 1:1,000,000 topographical charts for the area but the Investigation was unable to establish whether the flight crew had been using them for navigation. Available evidence indicated that there had been cloud along the mountain range en route which had necessitated tracking via a gap to the north west of destination. The wreckage was found to the north east of the route normally flown through the gap.
A successful readout of the CVR confirmed that there had been cloud in the area of the mountain gap where the aircraft wreckage had been found and that ‘marginal visual meteorological conditions for flight may have existed’. It was concluded that the gap itself had been obscured by cloud and that VFR had not been maintained with Controlled Flight Into Terrain (CFIT) being the unintended outcome.
The Investigation noted that an undamaged ELT had been recovered from the wreckage but that no signals from it had been picked up.
In respect of the Causes of the accident, the formal conclusion of the Investigation was that:
“The pilots did not maintain visual flight procedures when flying below lowest safe altitude, and the aircraft was flown into cloud in the vicinity of gap north west of Oksibil. The accident was consistent with controlled flight into terrain.”
Two Safety Recommendations were issued:
- That Merpati Nusantara Airline review its maintenance procedures and maintenance inspection programs, to ensure that Emergency Locator Transmitters are serviceable.
- That the Directorate General of Civil Aviation should liaise with the Meteorologi Klimatologi dan Geoficika (BMKG) to establish an aviation weather information service for all areas covered by civilian aircraft operators. This service could be enhanced by a network of government and mission out stations providing scheduled weather reports that the BMKG could promulgate to aircraft operators through the briefing offices and air traffic services. This service could be further enhanced by the same network of government and mission out stations providing updated weather reports when there is a significant change of weather between scheduled reports.
It was also determined that two other Safety Recommendations already made on 23 December 2009 in respect of the investigation into the loss of a Pilatus PC-6 Turbo Porter aircraft in West Papua in 2008 should be re-issued:
- That the Directorate General of Civil Aviation review the training and checking requirements for pilots operating in remote and mountainous regions such as Papua. Particular attention should be given to visual flight operations in mountainous and unpredictable weather conditions. This should include intensive route and aerodrome familiarization in locations, and over routes, where aids such as Terrain Avoidance and Warning System (TAWS), GPWS/TAWS, Global Positioning System (GPS) and Radio Altimeter are not effective, are not practical, or are not available.
- That the Directorate General of Civil Aviation should issue an urgent Notice To Airmen to remind pilots that flight below lowest safe altitude, in particular in mountainous regions, must be conducted in accordance with the Visual Flight Rules (VFR)
The Final Report of the Investigation KNKT.09.08.21.04 was completed in the second half of 2010.