The crew of a Cessna 550 aircraft had planned for a flight from Essendon, Vic to Bankstown, NSW at flight level (FL) 370. The aircraft departed and was given an initial altitude restriction of FL 200 by air traffic control (ATC). The crew were transferred to Melbourne Inner North control and the controller, having no conflicting traffic in the projected flight path of the C550, issued a climb instruction to FL 370. The pilot thought that the controller had said FL 300 and read back FL 300. This incorrect read back was not detected by the controller, who had indicated a read back of FL 370 on his flight progress strip.
Shortly after, the Inner North controller transferred the crew of the C550 to the en-route sector, Melbourne Sector 2. On first contact with Sector 2, the crew reported that they were on climb to FL 300. The Sector 2 controller considered this to be an unusual level and immediately contacted the Inner North controller to confirm the assigned cruising level. He was told that this was FL 370. The Sector 2 controller then asked the crew of the C550 if they would prefer FL 370 and, on receiving a positive reply, issued a climb instruction for the crew to climb to FL 370. This was correctly read back by the pilot and the flight proceeded to Bankstown without further incident.
It is normal operating practice for Sector 2 control to not have any planned levels on their flight progress strips. All aircraft coming into this sector are already under radar control and this rule reduces co-ordination between sectors and the number of level changes that may need to be recorded on the strip.
SIGNIFICANT FACTOR
The pilot of the C550 and the Inner North controller did not exercise sufficient vigilance in their radio listening techniques.