What happened
On 28 August 2015, a Boeing 737-300F, registration PK-BBY, was performing a scheduled cargo flight from Sentani to Wamena, Indonesia. While on final approach to runway 15, the aircraft encountered windshear conditions. The flight crew reduced engine thrust significantly, which led to a rapid descent. The aircraft touched down approximately 35 meters before the start of the runway pavement with a vertical acceleration of 3.68 G. This impact caused the left main landing gear to collapse and the left engine to make contact with the runway surface. There were no injuries to the two crew members on board.
The investigation
The KNKT investigation focused on the sequence of events leading to the undershot landing and the structural failure of the landing gear. Investigators analyzed flight data recorder (FDR) and cockpit voice recorder (CVR) information, which revealed that the EGPWS issued a "CAUTION WINDSHEAR" warning at 5,520 feet. Following this, the FDR showed engine N1 decreasing from 73% to 38%, while the airspeed decreased. The investigation also examined the maintenance history of the aircraft, noting that the operator had not yet implemented a system to monitor aircraft performance using flight recorder data. Furthermore, the investigation found that the Visual Approach Slope Indicator (VASI) for runway 15 was not operational at the time of the accident.
Findings
- The primary cause of the accident was a large thrust reduction during windshear, which resulted in a rapid descent and an undershot landing.
- The left main landing gear suffered a broken trunnion link, leading to its collapse.
- The aircraft's landing gear had likely suffered strength degradation due to a history of frequent high-vertical-acceleration landings (exceeding 2 G) that had gone unmonitored.
- The flight crew did not perform speed corrections following the reported headwind, and there was a lack of crew briefing regarding the windshear after the EGPWS alert.
- Air traffic controllers did not report gust wind information to the pilots, which could have alerted them to the windshear risk.
Safety action
Following the accident, PT. Cardig Air implemented several corrective measures, including establishing a flight data analysis system and conducting windshear training in simulators for its pilots. The KNKT issued safety recommendations to AirNav Indonesia to improve controller information regarding windshear, to Wamena Airport to reinstall the VASI and improve runway inspections, and to the Directorate General of Civil Aviation to ensure operators maintain robust flight data analysis programs.