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Final Report

Summary

What happened

On 11 February 2015, an Airbus A320 aircraft, registered VH‑VND and operated by Tiger Airways, was conducting a scheduled passenger service from Hobart Airport, Tasmania to Melbourne Airport, Victoria.

At about 1750 Eastern Daylight-saving Time, about 9 NM (17 km) north of Melbourne Airport, and after the flight crew had been cleared by air traffic control to conduct a visual approach, the aircraft descended below the minimum safe altitude, though the aircraft remained in controlled airspace.

During the descent, both flight crew became pre-occupied with other tasks inside the flight deck, which had the effect of increasing their workload and distracting them from monitoring the aircraft’s flight path and altitude. About two minutes after commencing descent on the visual approach, the flight crew levelled the aircraft after realising that it appeared to be low on profile. A safety alert issued by air traffic control soon followed, where in response, the aircraft was climbed to intercept the recommended visual approach descent profile. The remainder of the flight was uneventful and the aircraft landed on runway 16 at Melbourne Airport.

What the ATSB found

The ATSB found that after being vectored off the expected pre-planned shortened arrival route, and then cleared for a visual approach, a combination of increased workload and distraction diverted the flight crew’s attention from monitoring the aircraft’s descent. During the descent, the captain elected to intercept the final approach course by entering a radial intercept waypoint into the aircraft’s auto-flight system, which differed from the first officer’s more familiar plan to conduct a localiser intercept. This had the effect of diverting both crew members’ attention to inside the flight deck, as they discussed and demonstrated the intercept and resulting flight mode reversions. The aircraft continued to descend below the normal approach profile and entered the 500 ft vertical buffer at the base of the control area step. This reduced separation with terrain and any aircraft operating outside controlled airspace.

The flight crew’s mental model of the approach was not consistent with the actual flight path of the aircraft. This affected their ability to fly a normal descent profile and remain within the required control area step.

The flight crew miscalculated and did not adequately communicate the aircraft’s descent from 3,000 ft during the conduct of a visual approach. This limited their awareness of the descent rate and the below-profile altitude of the aircraft during a critical phase of flight.

Safety message

Flight crew should be mindful that during higher workload phases of flight, such as during approach and landing, introducing tasks that divert both flight crew members’ attention from monitoring the aircraft’s flight profile and altitude should be minimised. Further, if tasks that bring attention into the flight deck are required to be completed during a visual approach, pilots must ensure that at least one pilot monitors the aircraft’s flight path profile and energy state. Setting an appropriate lower altitude limit may be an effective risk control to alert flight crew and/or prevent the aircraft’s descent below a desired altitude. Communication and confirmation of any changes to the aircraft’s flight modes are also important during this period.

The occurrence

Context

Safety analysis

 
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