What happened
On 31 October 2016, a DHC-4A Caribou Turbo, registration PK-SWW, was performing a scheduled cargo flight from Timika to Kaminggaru Aerodrome in Ilaga, Papua. The aircraft, operated by Perkumpulan Penerbangan Alfa Indonesia, was carrying a 6,900 lb load and was manned by two pilots, a company engineer, and a flight operations officer.
During the flight, the pilot established contact with the Ilaga Flight Information Services Officer (FISO) at 23:23 UTC, reporting the aircraft's position at Ilaga Cut and providing an estimated arrival time. However, shortly after, the aircraft ceased all communications. A search and rescue operation later located the wreckage on a mountain ridge near Jila Pass at an elevation of approximately 13,000 feet. The impact resulted in 4 fatalities and the total destruction of the aircraft.
The investigation
The KNKT investigation focused on the aircraft's flight path, the functionality of the Terrain Awareness and Warning System (TAWS), and the integrity of the Cockpit Voice Recorder (CVR) data. Investigators examined the terrain databases used by the aircraft's navigation equipment and analyzed the wiring modifications made to the CVR system. The inquiry also reviewed the meteorological conditions and the pilot's compliance with visual flight rules (VFR) during the flight.
Findings
- The pilot was flying within cloud cover, which significantly reduced situational awareness regarding the surrounding mountainous terrain.
- The Terrain Awareness and Warning System (TAWS) did not function normally, failing to provide the necessary alerts to prevent the collision.
- The terrain database for the Papua region was of low resolution, which often triggers frequent, unnecessary warnings, leading pilots to potentially inhibit the system.
- A modification to the CVR wiring caused the cockpit area microphone channel to be overwhelmed by engine noise, rendering cockpit conversations and system alerts unidentifiable on the recording.
- The aircraft was operating in conditions that likely violated basic VFR weather minimums.
Safety action
The Indonesian Directorate General of Civil Aviation (DGCA) issued several safety circulars requiring operators to adhere to stabilized approach criteria and to cancel flights if meteorological conditions fall below minimums. The KNKT has issued recommendations to manufacturers regarding high-resolution terrain databases for the Papua region and urged operators to ensure that all post-modification system tests are properly documented and verified.