2009 Aviastar British Aerospace 146 crash

Investigation

The investigation was conducted by the National Transportation Safety Committee. At the time of the accident, the weather in Wamena was calm, with slight haze and broken clouds surrounding the area. Visibility was 8 km. The weather was not a factor in the crash. Investigators retrieved both the Flight Data Recorder and Cockpit Voice Recorder. Both had good quality data. Based on the analysis of the flight recorders, investigators then reconstructed the chronological order as follows:

At its first attempt to land, the runway in Wamena was obscured by low clouds. Knowing that they couldn't fly the aircraft to the established flight path for an approach, the crew abandoned the approach and started a go around to the right at a low height, approx 150 ft. While on the right circuit down-wind leg, the enhanced ground proximity warning system (EGPWS) warning sounded, eight of them were "Don't sink", two "Too low terrain", two "Bank Angle" and one "Terrain Terrain" voice aural alerts. The flight crew did not respond to any of those alerts. First Officer Lukman became really concerned with Captain Sigit's handling of the aircraft. He later said "be careful, Sir" to Captain Sigit.

The aircraft then increased its bank angle to the right. First Officer Lukman became really anxious, saying "Sir Sir Sir open Sir left left". Shortly afterwards Captain Sigit banked the aircraft to the left. The "Don't sink" alert sounded for the second time. The bank angle to the left became extreme, exceeding 40°. The aircraft also entered a 10-degree nose down pitch attitude. First Officer Lukman then warned Captain Sigit "don't sink". In repeating the words "don't sink", First Officer Lukman was alerting Captain Sigit to comply with the EGPWS voice aural alert "Don't sink, don't sink". Captain Sigit immediately responded "ya, ya".

Three seconds later, Lukman urgently commanded "left turn". The EGPWS voice alert then sounded, "Too low, terrain", "bank angle, bank angle" "terrain – terrain" warning. At the same time, First Officer called to Captain Sigit "sir! sir! sir!". The aircraft then impacted the ground.

NTSC noted that there was not good crew resource management throughout the flight. Neither pilot was trained sufficiently in handling the aircraft when the EGPWS warning alert sounded. The Company Operations Manual (COM) specified that the crew briefing should be updated if changing circumstances so required. Captain Sigit did update the briefing when the first approach was discontinued and the go-around was conducted. Captain Sigit's disregard of the EGPWS alerts that sounded as the aircraft was being maneuvered was in non-conformance with the instructions for crew response to EGPWS alerts and cautions, as published in the COM. That, together with their lack of flight crew training in EGPWS, meant that they had not been properly prepared to respond in a timely and appropriate manner to the alerts and warnings provided by the EGPWS. Had Captain Sigit executed the appropriate responses to those EGPWS alerts it is unlikely that the crash would have occurred.

Neither flight crew member conformed to the instructions about flight crew responsibilities during a visual approach, as published in the COM. This resulted in their being unable to assure the safety of flight at low level while manoeuvring the aircraft in proximity with terrain in conditions of reduced visibility. Had they more carefully planned the second approach, and closely cooperated with each other, they may have achieved a safe approach and landing. Their disregard of the published procedures bypassed the safety criteria and inbuilt risk treatments in the design of those procedures.