Controlled Flight Into Terrain, Indonesia Air Transport (Atr 42-500 PK-THT) Mount Bulusaraung, Maros, South Sulawesi, KNKT.26.01.01.04

On 17 January 2026, an ATR 42-500 aircraft, registration PK-THT, was being operated on an unscheduled flight from Adisutjipto Airport (WAHH), Yogyakarta, Indonesia, with the intended destination of Sultan Hasanuddin International Airport (WAAA), Maros, Indonesia. The aircraft was chartered for an aerial surveillance mission and was planned to conduct an aerial surveillance over four areas.

On board the aircraft were two pilots, two flight attendants, and six passengers: one flight operation officer, two aircraft engineers, and three aerial surveyors.

The Flight Data Recorder (FDR) of the aircraft recorded the Global Navigation Satellite System (GNSS) on degrade mode during most of the flight operation. The aircraft position recorded in the FDR was different from the aircraft position recorded in the ground receiver of Automatic Dependent Surveillance–Broadcast (ADS-B). The recorded aircraft coordinate in the FDR was the aircraft position displayed in the EHSI, and the ADS-B data were utilized by the air traffic services (ATS) provider for its surveillance system to display the aircraft target on the air traffic controller (ATCO) situation display.

At 0109 UTC, the aircraft departed from Runway 09 of Adisutjipto Airport and climbed to the cruising altitude of 11,000 feet. The flight was then provided with air traffic control services and flight information services.

At 0348 UTC, the PM made initial contact with the ATCO of Ujung Pandang Terminal Control Area (TMA). Thereafter, the PK-THT pilot was instructed to make an approach to Runway 21 using the Instrument Landing System (ILS). Cockpit Voice Recorder (CVR) data indicated that the SIC was the PM and the PIC was the PF.

The ATCO provided air traffic control services utilizing a surveillance system and was accompanied by one planner (assistant controller).

At 0423 UTC, the PK-THT target on the ATCO situation display changed from a surveillance target to a flight plan target, meaning that the surveillance system did not receive PK-THT surveillance data. The ATCO repeatedly called the PK-THT pilot. The efforts were unsuccessful in obtaining any responses from the PK-THT pilot.

The search and rescue mission was immediately activated after the Air Traffic Services (ATS) provider notified the Indonesia Search and Rescue Agency (BASARNAS), and on 18 January 2026, the aircraft was found scattered on Mount Bulusaraung. All persons on board were fatally injured in the occurrence, and the aircraft was destroyed by the impact force.

The investigation involved the participation of the Bureau d’Enquêtes et d’Analyses pour la sécurité de l’aviation civile (BEA) France as the State of Design and the State of Manufacture, and the National Transportation Safety Board (NTSB) of the United States of America as the State providing assistance. Both agencies have appointed their accredited representatives to assist in this investigation in accordance with the provisions in ICAO Annex 13.

The investigation is ongoing. Should any further relevant safety issues emerge during the course of the investigation, KNKT will immediately bring the issues to the attention of the relevant parties and publish them as required.