The ATSB is investigating an incident in which a Virgin Australia 737-800 was incorrectly flown toward its cruising altitude at a fixed mach value, causing the airspeed to decline toward a loss of control situation is under investigation by.
The ATSB states: “On 4 January 2013, a Boeing 737-8FE aircraft, registered VH-VUZ, was operating a scheduled passenger service from Launceston, Tasmania to Melbourne, Victoria. Soon after takeoff, the auto-flight system was selected to Level Change mode. In this mode, the aircraft climbed at a constant airspeed to about flight level 260, when the auto-flight system sequenced automatically to continue the climb at a constant Mach number. The flight crew, who were experiencing a relatively high workload at the time associated with the short sector, intended to switch to a different vertical mode during the climb that would have allowed the aircraft to accelerate in accordance with a programmed speed schedule. However, they overlooked that selection and unintentionally continued to climb in Level Change mode.
“As the aircraft continued to climb at a constant Mach number, the airspeed slowly reduced. The crew did not detect the reducing airspeed until the aircraft was approaching the minimum manoeuvre speed at about FL 350. In responding to the low speed condition and attempting to accelerate, the crew reduced the aircraft pitch attitude to the point that the aircraft entered a shallow descent. Soon after, the crew was able to establish an accelerated climb to the intended cruising level.
“The investigation is continuing with a focus on the human factors issues associated with auto flight system mode awareness. It is expected to be completed in November 2013.”
ATSB investigates Virgin Australia 737 incident
