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.
|Date:||07 April 2009||Investigation status:||Completed|
|Time:||1210 EST||Investigation level:||Complex - click for an explanation of investigation levels|
|State:||New South Wales||Occurrence type:||Avionics/flight instruments|
|Release date:||01 February 2010||Occurrence class:||Technical|
|Report status:||Final||Occurrence category:||Incident|
|Highest injury level:||None|
|Aircraft manufacturer||The Boeing Company|
|Type of operation||Air Transport High Capacity|
|Damage to aircraft||Nil|
|Departure point||Hobart, Tas.|