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Report: Misunderstood clearance causes B747F to descend below minimum permitted altitude
6 September 2015
Aircraft radar trac (Airservices Australia (modified by the ATSB))

Aircraft radar track (Airservices Australia (modified by the ATSB))

A descent clearance that was misunderstood by the crew of a Boeing 747 cargo plane led to a descent below minimum permitted altitude during the approach to Melbourne Airport, Australia, according to an ATSB investigation report.

On 9 September 2012, a Boeing 747-400F cargo aircraft, operated by Atlas Air and registered N409MC, was approaching runway 34 at Melbourne Airport, Australia following a flight from Auckland, New Zealand.

The flight crew was conducting the LIZZI FIVE VICTOR standard arrival route (STAR) procedure that included a requirement not to descend below 2,500 ft until past the SHEED waypoint. They were issued clearance by air traffic control for a visual approach for runway 34 from the SHEED waypoint, conditional on not descending below 2,500 ft before SHEED. The flight crew read back the clearance without including the minimum altitude before passing SHEED and the controller did not query the incomplete read back. The flight crew initiated the visual approach and descended below the stipulated minimum of 2,500 ft prior to SHEED.

The ATSB found that the United States-based flight crew did not hear the requirement of the clearance to not descend until after passing the SHEED waypoint. Instead they read back what they believed to be a clearance for an immediate visual approach from their present position. This is a normal instruction during operations in United States airspace. The crew continued their approach to Melbourne Airport based on this understanding. There was no loss of separation with any aircraft.

The lack of detection by the controller of the crew’s incomplete read back represented a missed opportunity to alert the flight crew to not descend below 2,500 ft until after the SHEED waypoint.

Visual approaches from STARs are available elsewhere in Australia, but are not available for use by international operators of large jet aircraft. The approaches via SHEED to runway 34 at Melbourne are the only exception to this rule and are implemented with few additional defences to address the increased risk associated with this type of approach. In addition, the flight profile required from the SHEED waypoint to runway 34 is steeper than other approaches of this type in Australia, requiring a higher rate of descent. This increases the likelihood of an unstable approach.

As a result of this occurrence, Airservices Australia is removing the provision in the Manual of Air Traffic Services for international Heavy and Super Heavy aircraft to use the SHEED visual segment. This permanent change to the Manual of Air Traffic Services is planned for November 2015, with a temporary local instruction to that effect to be issued by Airservices in the interim. In respect of the descent profile of the LIZZI FIVE RWY 34 VICTOR ARRIVAL, the Civil Aviation Safety Authority will engage with Airservices to ensure that the procedure meets all relevant instrument procedure design and ‘flyability’ standards.

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