ANSP info/procedural error involving a Boeing 747-400, N117KG, 1310 km north of Perth, Western Australia, on 26 October 1993

The Air Traffic Service (ATS) Officer issued a clearance for the aircraft to climb from FL330 to FL370. The crew did not receive the clearance. The ATS Officer did not realise he had not received an acknowledgement to the clearance and assumed the aircraft had climbed to the assigned level. He later misunderstood a further request from the crew for information about the climb clearance to be a statement that the aircraft was cruising at the new level.

Consequently, the aircraft transited between two reporting points at the incorrect flight level. The error was discovered when the aircraft reported its level at the next reporting point. No traffic confliction resulted.