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The Departures North radar controller was radar vectoring a Boeing 737 (B737) for a right downwind leg to runway 34R and had instructed the crew to descend to 7,000 ft, which was correctly read back. Subsequently, the controller observed the mode C altitude radar display for the aircraft indicating that it was descending through 6,400 ft. The controller requested that the crew confirm the assigned altitude and was advised that they had been assigned 5,000 ft. The controller instructed the crew to climb the aircraft to 7,000 ft. There was no infringement of separation standards; however, the B737 was being vectored to overfly a De Havilland Twin Otter, and vertical separation standards were being applied.

An investigation by the operator established that the pilot in command (PIC) had selected 5,000 ft in error, and that a cross-check of the altitude setting by the co-pilot had been obscured by sun reflections on the instrument panel. The PIC believed that he may have overheard the assignment of 5,000 ft to the crew of another aircraft at the time he was resetting the altitude indicator. At the same time, the purser entered the cockpit and this action may have distracted the PIC so that he only remembered the last altitude transmitted, and not that actually assigned to his aircraft.

 

Local safety action

As a result of this investigation, the operator issued a safety notice to flight crew advising the circumstances of the occurrence, and emphasising the need for sterile flight deck requirements during critical phases of flight.

 
General details
Date: 01 January 1995 Investigation status: Completed 
Time: 0710 hours EST  
Location   (show map):22 km N Sydney, (VOR) Investigation type: Occurrence Investigation 
State: New South Wales  
Release date: 01 February 1999  
Report status: Final Occurrence category: Incident 
 Highest injury level: None 
 
Aircraft details
Aircraft manufacturer: The Boeing Company 
Aircraft model: 737 
Aircraft registration: VH-TAX 
Serial number: 23489 
Type of operation: Air Transport High Capacity 
Damage to aircraft: Nil 
Departure point:Brisbane, QLD
Destination:Sydney, NSW
 
 
 
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Last update 19 May 2016