Merpati Nusantara Airlines Flight 9760D

Investigation

The Indonesian National Transportation Safety Committee (NTSC) opened an investigation into the accident. The cause was found to be controlled flight into terrain. In the report, Merpati Nusantara Airlines were stated not to have fully co-operated with the NTSC as they had not provided the investigators full details of the crew's line checks and training undertaken.

The National Transportation Safety Committee found that there were no maintenance defects found on the aircraft. The aircraft was also loaded with cargo within limits, ruling out overloading. The weather in the area of the flight was reported by local villagers to have been mostly clear in the valleys, with clouds on the mountains and slopes. About 25 minutes prior to the accident, the crews contacted another crew from a Lockheed C-130 Hercules aircraft owned by the Indonesian Air Force which was flying from Oksibil to Sentani and said that they were 100 miles from Jayapura en route to Oksibil. The pilot of the Hercules informed the crew of Flight 9760D that over Oksibil the cloud base was low, with cloud tops between 6000 and 7000 ft. As the cloud tops were 12500 ft, the Hercules pilot informed the crew of Flight 9760D they would have to detour via Kiriwok to avoid the clouds.

The aircraft was not equipped with a flight data recorder (FDR). Indonesian regulations did not require a FDR to be fitted to the Twin Otter aircraft. However, the aircraft was equipped with a Cockpit Voice Recorder (CVR). Indonesian Civil Aviation regulations required that a serviceable CVR was to be fitted to the Twin Otter aircraft. Search and Rescue personnel recovered the CVR from the wreckage and handed it over to NTSC investigators. The outer box had minor damage, but the contents were undamaged. About 20 minutes before the impact, the pilots were discussing the area they were flying over, and made comments about the local inhabitants. Fifteen minutes before impact, the pilot in command said to the copilot "Let's fly direct Oksibil". The copilot asked "Direct brother?" The PIC replied "Direct, the sky is blue over there and the layer of the cloud is 10,000 feet". One minute later the copilot gave a position report to ATC stating: One two three zero traffic, Merpati nine seven six zero delay, Sentani to Oksibil, position approaching Melam maintain nine thousand five hundred, estimate Abmisibil zero two zero one, arrival zero two zero eight. This transmission was blocked by other transmissions and there was no evidence on recorded communications that the position report was acknowledged by ATC.

During the 20 minutes before the impact there was no discussion about aircraft problems or navigation difficulties. However, ten minutes before impact the pilot in command mentioned climbing to 10000 ft, and stated "if we cannot go visual I will turn left". The cockpit conversations did not exhibit any signs of stress or concern until 2 minutes before the impact, when the copilot mentioned haze and asked the pilot in command if he could see. Fifty seconds before impact, the copilot expressed further concern and asked about the pilot in command’s intentions, and the pilot in command said "climb, to the left". Forty-two seconds before impact the copilot asked if it was safe on the left. The copilot became increasingly uncertain about the safety of the flight, specifically mentioning visibility and speed. From the recorded sounds, it is apparent that 13 seconds before impact, engine power was increased symmetrically to a high power setting. From the pilots' comments and the wreckage trail, the investigation determined that the aircraft was banking left at the time of impact. The investigation was unable to determine if the aircraft reached 10,000 feet. The impact was at 9300 ft.