Aviation safety investigations & reports

Aero Commander 500-B, VH-YJO and Airbus Industrie, ZK-OJG, 22 km East Melbourne

Investigation number:
Status: Completed
Investigation completed


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.    
State: Victoria   Occurrence type: Avionics/flight instruments  
Release date: 25 February 2005   Occurrence category: Incident  
Report status: Final   Highest injury level: None  

Aircraft 1 details

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 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  
Last update 16 February 2016