Aviation safety investigations & reports

Avionics system event - Boeing 737-800, VH-VYL, Sydney Airport NSW, 7 April 2009,

Investigation number:
Status: Completed
Investigation completed


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On 7 April 2009, at about 1210 Eastern Standard Time, the flight crew of a Boeing 737-800 aircraft, registered VH-VYL, received an enhanced ground proximity warning system alert during an approach to land at Sydney Airport, NSW. At the same time, the autopilot disconnected and the engine thrust levers moved towards idle. The handling pilot corrected the engine thrust levers immediately and conducted an uneventful landing.

The investigation determined that spurious data from the left radio altimeter (RA) provided an indicated altitude of minus 7 ft, resulting in the autopilot disconnecting and the thrust lever movement.

An examination found that the left RA receive antenna displayed rubbing wear adjacent to the attachment screw inserts. A bonding check of the antenna indicated that the antenna's resistance was outside the aircraft manufacturer's limits. The antenna was replaced and the aircraft was returned to service.

Three months after the occurrence, a further RA warning flag event was experienced by another crew in this aircraft. As a result of that event, the left and right RA transceivers were removed and tested with internal faults found on the left unit.

Download Final Report
[Download  PDF: 433KB]
General details
Date: 07 April 2009   Investigation status: Completed  
Time: 1210 EST   Investigation level: Systemic - click for an explanation of investigation levels  
Location   (show map): Sydney Aerodrome    
State: New South Wales   Occurrence type: Avionics/flight instruments  
Release date: 01 February 2010   Occurrence category: Incident  
Report status: Final   Highest injury level: None  

Aircraft details

Aircraft details
Aircraft manufacturer The Boeing Company  
Aircraft model 737  
Aircraft registration VH-VYL  
Serial number 34184  
Type of operation Air Transport High Capacity  
Damage to aircraft Nil  
Departure point Hobart, Tas.  
Destination Sydney, NSW  
Last update 03 April 2020