In addition to the two go-arounds, the ATSB final report into the February 19 2016 incident found the flight crew twice flew too low while attempting to land after a number of unresolved system failures were “not properly managed”, leading to a degraded systems capability for the approach and an increased workload for the flight crew.
Further, the ATSB report said the flight crew’s lack of understanding of how the systems interacted led to inappropriate system selections.
“The unresolved system failures, combined with the conduct of a missed approach procedure and the subsequent runway change increased the flight crew’s workload,” the ATSB said.
“This likely reduced their ability to analyse the actual extent to which their automation was degraded, and effectively manage the subsequent approaches.”
The Indonesia AirAsia Airbus A320 PX-AXY was enroute from Denpasar to Perth and about an hour from arrival when when the flight crew noticed the captain’s multipurpose control and display unit (MCDU), used to enter flight planning into the flight management guidance system and display various flight navigation information, had frozen and the captain’s navigation display (ND) had the advisory message “MAP NOT AVAIL”.
Further, the ATSB report said the first officer’s MCDU displayed the message “INDEPENDENT OPERATION”, indicating the captain’s flight management and guidance computer (FMGC) had failed. The FMGC provides aircraft navigation, lateral and vertical guidance and aircraft performance functions along a pre-planned flight route.
A short time after this was discovered, the captain, who had about 13,500 hours flying experience including 5,200 hours on the A320, disengaged the autopilot and the flight crew decided to continue onto Perth using the first officer’s MCDU and NC, given his FMGC “appeared to be operating normally”, the ATSB said.
Prior to descent, the flight crew used the first officer’s MCDU to program the arrival procedure into Perth and the instrument landing system (ILS) approach for Runway 21.
And as the aircraft descended below 9,000 feet, the captain took over the role as the pilot monitoring, while the first officer became the pilot flying “as they believed it was better for the PF to have the functioning ND and MCDU”.
When the aircraft descended through 5,000 feet, the flight crew received the first of three speed restrictions from air traffic control (ATC), which required a change from a managed speed mode to a selected speed mode to control the aircraft’s speed.
Three minutes later, the flight crew received a warning that the elevation of the landing airport was not available from the FMGC and consequently, the landing elevation had to be manually selected.
One minute later, the aircraft intercepted the glideslope for the Runway 21 ILS.
“A short time later, the flight crew elected to select a managed speed mode,” the ATSB report said.
“This change resulted in the auto flight system attempting to capture the speed target contained in FMGC1 when it failed (which was 253 kt) and the autothrust system commanded an increase in engine thrust.
“The flight crew recognised the increasing engine thrust and airspeed but they did not understand why it occurred.
“The captain told the first officer, ‘make a go-around’ and then advised ATC that they were conducting a go-around.”
Then followed a period of 25 seconds where dual sidestick control inputs occurred. When the aircraft was at 2,500ft the captain took control of the aircraft and conducted the go-around.
The captain then vectored the aircraft for a VHF Omni Directional Radio Range (VOR) approach to Runway 06, choosing to disengage the autopilot and auto thrust and manually fly the aircraft due to his uncertainty over the thrust increase during the previous approach”.
“The first officer later recalled programming FMGC2 for the VOR approach, and briefing the captain for the approach,” the ATSB report said.
“The first officer also cross-referenced the information in the FMGC with his paper copy of the instrument approach chart.
“The captain stated that they conducted a short briefing instead of a full briefing because the situation was moving so quickly.”
The ATSB report said the first officer, who had 4,200 hours flying experience including 3,100 hours on the A320, was monitoring the descent gradient and vertical speed and “later recalled believing that they were on the correct descent profile”.
“However, for most of the descent, the aircraft’s rate of descent exceeded the recommended rate (700 ft/min) that was published on the approach chart for the aircraft’s groundspeed,” the ATSB report said, noting the maximum recorded rate of descent was 1,500ft/min.
Then, as the flight crew was attempting to establish visual contact with the runway and seeking ATC advice if they were on the “left side of the runway or the right side of the runway”, the ATC radar displayed a minimum safe altitude warning (MSAW).
“In response, the approach controller instructed the flight crew to ‘go round, you are low, low altitude alert, go round’,” the ATSB report said.
The flight crew acknowledged the alert and immediately conducted a missed approach, representing a second go-around.
The ATSB found the aircraft had descended to an altitude of 1,473ft, before the climb was initiated, which was about 400ft below the segment minimum safe altitude.
The flight crew then attempted to land for a third time, with a VOR approach to Runway 06.
At 2,500ft, and with the Captain as the pilot flying on the final approach track to Runway 06, the ATSB report said the flight crew “selected the FCU altitude to the minimum descent altitude for the VOR approach, again contrary to the operator’s procedure for conducting a non-precision instrument approach”.
Further, due to the late commencement of the descent from 2,500ft, the aircraft exceeded the recommended rate of descent (700 ft/min) for the aircraft’s groundspeed until 1,100 ft above the height of the runway threshold, averaging 1,380ft/min in a 40-second period when the aircraft descended from about 2,100ft to 1,200ft.
And while the vertical speed did drop below 700ft/min when the aircraft was at about 1,000ft above the height of the runway threshold, it increased to a maximum of 1,100ft/min for a 22-second period when the aircraft descended from 430ft to 120ft.
“At 300 ft AGL, the engine thrust reduced briefly to idle and at this point, the aircraft did not meet the stabilised approach criteria,” the ATSB said.
The aircraft landed without further incident.
It was not the first time the ATSB has investigated the airline group for incidents involving non-precision approaches at Australian airports.
The report noted three separate incidents – two in May 2010 and another in September 2016 – when a Malaysia AirAsia X Airbus A330-300 aircraft descended below the segment minimum safe altitudes.
The ATSB report said Indonesia AirAsia had implemented additional classroom sessions on aircraft line-check into its retraining program and added this incident as a subject of its simulator syllabus.
The full report can be read on the ATSB website.