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The Australian Transport Safety Bureau did not conduct an on-scene investigation of this occurrence. The report presented below was prepared essentially from information supplied to the Bureau.


At 0745 eastern summer time, on 12 January 2005, the pilot of Aero Commander Division 500-B, (Aero Commander) registered VH-YJO, was climbing to an assigned altitude of 5,000 ft enroute from Essendon to Wangaratta Victoria. An Airbus A320, registered ZK-OJG, was inbound to Melbourne on a crossing track at 6,000 ft. The vertical separation standard required between the two aircraft was 1,000 ft. The Aero Commander was observed on radar by air traffic control (ATC) to climb to about 5,300 ft. ATC requested that the pilot clarify the aircrafts altitude and the aircraft was observed to descend back towards the assigned altitude. The pilot reported that, at the time ATC queried his altitude, the aircraft altimeter read 5,100 ft. That was within the normal flight tolerance of plus or minus 100 ft for IFR flight specified in Civil Aviation Order 40.2.1.

Prior to the flight, the pilot conducted an accuracy check of the aircrafts altimeters as part of normal pre-flight checks. Those checks indicated that both aircraft altimeters were within IFR altimeter tolerances. On the return flight to Essendon later that day, the pilot carried out a check of the aircraft transponder with Melbourne Centre. That check indicated an aircraft altimeter reading of 6,060 ft, and a corresponding radar-derived altitude of 6,200 ft.

After the aircraft landed at Essendon, the operator conducted a maintenance check of the transponder encoder. That check determined that the encoder was over-reading by 140 ft. The operator took maintenance action to correct the anomaly.

While the aircraft altimeter confirmed the pilot was within normal IFR flight tolerance, the encoder anomaly contributed to the radar-derived apparent error in the pilots cruising level. Had the anomaly in the encoder not been present, this incident would not have occurred.

General details
Date: 12 January 2005 Investigation status: Completed 
Time: 0740 hours ESuT  
Location   (show map):22 km E Melbourne, Aero. Investigation type: Occurrence Investigation 
State: Victoria Occurrence type: Avionics/flight instruments 
Release date: 25 February 2005 Occurrence class: Technical 
Report status: Final Occurrence category: Incident 
 Highest injury level: None 
Aircraft 1 details
Aircraft manufacturer: Aero Commander 
Aircraft model: 500 
Aircraft registration: VH-YJO 
Type of operation: Charter 
Damage to aircraft: Nil 
Departure point:Essendon, VIC
Departure time:2040 hours ESuT
Destination:Wangaratta, VIC
Aircraft 2 details
Aircraft manufacturer: Airbus Industrie 
Aircraft model: A320 
Aircraft registration: ZK-OJG 
Type of operation: Air Transport High Capacity 
Damage to aircraft: Nil 
Departure point:Christchurch, NZ
Departure time:1724 hours ESuT
Destination:Melbourne, VIC
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Last update 16 February 2016