ATR 42-512

Indonesia Air, opb Mar. and Fisheries Res Surveillance

An Indonesia Air ATR 42-512, operating for the Marine and Fisheries Resources Surveillance (PSDKP) impacted a mountainside while approaching the destination, Makassar-Sultan Hasanuddin International Airport (UPG). All seven crew members and three passengers were killed. The aircraft departed Yogyakarta, bound for Makassar (UPG) on a maritime patrol mission. After engine start, and the FDR recorded the parameter of the GNSS HT1000 as "Degrade", which means that the GPS accuracy or integrity was compromised. A DGR amber alarm would have been displayed on the Electronic Horizontal Situation Indicator (EHSI) – a display in the cockpit that can be used by the pilot to indicate the aircraft position. Initially the system was off by 1 nautical mile. The flight took off from Yogyakarta Airport at 01:19 UTC (08:19 local time). At 01:14 UTC, when the aircraft passed an altitude of 7700 feet, the GNSS switched to "Not Degrade". About 30 minutes later, the the GNSS parameter reverted to "Degrade" again. As the flight continued, the distance between the actual position of the aircraft and the one reported by the GPS increased to 15 NM. As it approached the destination airport, the aircraft received instructions from air traffic control (ATC) to intercept the runway 21 ILS via waypoint OPENG at 5,300 ft. ATC noticed that the aircraft had passed the waypoint and requested it to proceed directly to Final 21. The pilot then requested a radar vector to waypoint KABIB, which is the Initial Fix (IF), but the aircraft had already passed this point. ATC then guided the aircraft to intercept the final approach on a heading of 240°, later corrected to 250°. The MSAW from the ATC surveillance system did not activate when the the aircraft target was below the minimum safe altitude described in the ATC Minimum Surveillance Altitude Chart (SMAC). About 04:22 UTC (13:22 local time), the aircraft’s EGPWS generated aural alerts “TERRAIN - TERRAIN” followed by “PULL UP” four times. The aircraft impacted a cliff on Mount Bulusaraung, with debris falling into a ravine below. The wreckage coordinates reported by the search and rescue agency Basarnas point to a 4327 feet peak, 14 nm north-east of the threshold of runway 21. Minimum Sector Altitude in the area is 8500 feet with an ATC surveillance minimum of 6000 feet.