The flight crew of an AirAsia X Airbus A330 did not follow proper procedures when faced with an engine oil pressure warning, attempting to restart the affected engine even after it had failed, as well as electing to divert to Melbourne when the aircraft was considerably closer to two other airports in an August 2016 incident, according to a recently released report from the Australia Transport Safety Bureau (ATSB).
The engine oil pressure warning and subsequent engine failure occurred during a 16 August 2016 scheduled flight from Sydney to Kuala Lumpur, with two flight crew, eight cabin crew and 234 passengers on board. While in cruise near Alice Springs the flight crew received an “Engine 2 oil low pressure” failure alert message, which the ATSB’s subsequent investigation of the event established was due to a shaft failure in the engine’s oil pressure pump. That alert required immediate crew action comprising of reducing thrust on the affected Rolls-Royce Trent 700 engine to idle and then, in accordance with the Airbus procedure, “if [the] warning persists”, shutting down the engine.
The ATSB report said the flight crew “probably misinterpreted” the term “persists” as requiring they wait a certain period of time to determine if the condition was persisting. As a result, they continued to troubleshoot the failure, rather than shut down the engine. “After monitoring the engine the flight crew formed the view that the warning was the result of a gauge failure,” the report said, and the crew then “increased the engine’s thrust. This led to the engine stalling and ultimately failing”.
The crew erroneously determined that the failed engine was not damaged and could be restarted and “contrary to the operator’s procedures, the flight crew made two attempts to restart the failed engine, even though there was no safety risk to the aircraft that demanded a restart attempt. Both attempts failed.”
Also contrary to the operator’s procedures, the flight crew elected to divert to Melbourne following the engine failure, rather than to closer suitable airports in Alice Springs and Adelaide, according to the ATSB report. Although twin-engine airliners such as the A330 are designed to fly safely on a single engine, “this decision increased the time that the aircraft was operating in an elevated risk environment of single-engine operations”, the ATSB said.
“There are three key safety messages from this investigation,” noted ATSB Director Transport Safety Dr Stuart Godley. “Not only does this occurrence demonstrate the importance of flight crews adhering to standard operating procedures when responding to aircraft system alerts, it also highlights that those procedures need to be designed with clarity,” Godley said. “Further, the investigation report identifies that where there is not a need for an immediate response, that flight crews look at the full contextual and available information before deciding on a plan of action.”
Since the incident, AirAsia X restated the operational requirements for flight crews for engine restarts and diversion decision making. Further, the airline has also used the occurrence as the basis for a training package for responding to engine failures, restarting failed engines, and diversion decision making.
This is not the first time AirAsia has had problems in Australia. In 2015, an AirAsia flight from Sydney to Malaysia ended up in Melbourne after the pilots entered the wrong coordinates into the internal navigation system. According to an ATSB report on the incident, the problem occurred when faulty earmuffs prompted the captain and first officer to swap their usual pre-flight checks. Ordinarily, the report said, the captain would conduct an external inspection of the plane while the first officer stayed in the cockpit and, among other tasks, completed the position initialisation and alignment procedures. On this day, however, the captain’s ear protection was not available so he took over the cockpit tasks, which included entering their current coordinates, usually given as the coordinates of the departure gate, into the plane’s internal navigation system. The report said that the captain manually copied the coordinates from a sign outside the cockpit window into the system, and that later analysis showed a “data entry error”.
The report said the crew had “a number of opportunities to identify and correct the error” but did not notice it until they had become airborne and started to track in the wrong direction. Those opportunities included a flag or message that flashed up on the captain’s screen during crosscheck of the cockpit preparations, which the first officer later told ATSB investigators he had seen but not mentioned because it was “too quick to interpret”; and three separate chimes which, because they were not accompanied by a message from the computer, were ignored. A fifth sign that something was wrong came in the form of an alert blaring: “TERRAIN! TERRAIN!” This was not ignored – both pilots said it had “startled” them. But, as that alert meant they were about to hit something and they could see the way ahead was clear, and as the busy runways at Sydney airport made the full response to such an alert “undesirable”, they pressed on. However, when autopilot engaged at 410 feet, it tracked the plane left, toward the flight path of another runway.
Both the captain and the first officer tried to fix the system but “attempts to troubleshoot and rectify the problem resulted in further degradation of the navigation system, as well as to the aircraft’s flight guidance and flight control systems”, the ATSB said.
The ATSB said “even experienced flight crew are not immune from data entry errors” and advised AirAsia to upgrade its flight systems to assist in preventing or detecting such errors in future.
Air Asia said it upgraded its flight management systems on its Air Asia X planes, sent a training bulletin to staff emphasising the correct operation and alignment of the flight data system, and had briefed all pilots on the findings of its internal investigation.