Investigation number
200500074
Occurrence date
Location
22 km E Melbourne, Aero.
State
Victoria
Report release date
Report status
Final
Investigation type
Occurrence Investigation
Investigation status
Completed
Aviation occurrence category
Avionics/flight instruments
Occurrence class
Incident
Highest injury level
None

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.

REPORTED INFORMATION

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.

Aircraft Details
Manufacturer
Aero Commander
Model
500
Registration
VH-YJO
Operation type
Charter
Sector
Piston
Departure point
Essendon, VIC
Departure time
2040 hours ESuT
Destination
Wangaratta, VIC
Damage
Nil
Aircraft Details
Manufacturer
Airbus
Model
A320
Registration
ZK-OJG
Operation type
Air Transport High Capacity
Sector
Jet
Departure point
Christchurch, NZ
Departure time
1724 hours ESuT
Destination
Melbourne, VIC
Damage
Nil