The pilots of an Air Asia flight to Perth that flew 200m too low had a limited understanding of how the flight management guidance computer would affect the use of the aircraft’s automated systems, a report has found.
The incident happened late on February 19, 2016 as the pilots of flight QZ536 made their final approach to Perth Airport’s runway 06 over Dalkeith towards South Perth.
According to the Australian Transport Safety Bureau report issued this morning “during the flight down from Bali, the captain’s flight management and guidance computer (FMGC1) failed.
“Due to the failure, the flight crew elected to use the first officer’s duplicate systems. For the aircraft’s arrival in Perth there was moderate to severe turbulence forecast below 3,000 ft with reports of windshear. The crew commenced an instrument landing system (ILS) approach to runway 21” the report said.
The report said that during the [first] approach, the flight crew made a number of flight mode changes and autopilot selections, however some of those flight modes and autopilot selections relied on data from the failed FMGC1 and the autothrust system commanded increased engine thrust.
The ATSB said that “the crew did not expect this engine response and elected to conduct a go-around.”
But with an increasing crosswind on runway 21, the crew accepted a change of runway, to conduct a non-precision instrument approach to runway 06.
“During the approach to runway 06, the crew descended the aircraft earlier than normal, but believed that they were on the correct flight path profile,” the ATSB said.
“While descending, both flight crew became concerned that they could not visually identify the runway, and focused their attention outside the aircraft. At about that time, the approach controller received a “below minimum safe altitude” warning for the aircraft. The controller alerted the crew of their low altitude and instructed them to conduct a go-around. The crew then conducted another approach to runway 06 and landed.”
The ATSB said that it “identified that the flight crew were unsuccessful in resolving the failure of the FMGC and had a limited understanding of how the failure affected the aircraft’s automation during the ILS approach. This resulted in the unexpected increase in engine thrust, which prompted a go-around.”
It added that “the flight crew had a significant increase in workload due to the unresolved system failures, the conduct of a go-around and subsequent runway change. This, combined with the crew’s unfamiliarity and preparation for the runway 06 instrument approach, meant they did not effectively manage the descent during that approach.”
“The flight crew’s focus of attention outside the aircraft distracted them during a critical stage of flight. The crew did not detect that they had descended the aircraft below the specified segment minimum safe altitude.”
The ATSB said that it is essential for flight crew to “adherence to standard operating procedures and correctly monitoring the aircraft and approach parameters provides assurance that the instrument approach can be safely completed.”
It warned that “a go-around should be immediately carried out if the approach becomes unstable or the landing runway cannot be identified from the minimum descent altitude or missed approach point.”
See Indonesia AirAsia’s safety rating here; https://www.airlineratings.com/ratings/airasia-indonesia/