AIP ENR 1.1 General Rules
Operations in Controlled Airspace
Descent and Entry--
11.1.4 After any frequency change, pilots must advise the last assigned
level and, if not maintaining the assigned level, the level maintaining
or last vacated level; eg, “MELBOURNE CENTRE (CALLSIGN)
CLEARED FLIGHT LEVEL TWO ONE ZERO, LEFT
FLIGHT LEVEL TWO NINER ZERO”.
Serious question to Bona Fide ATC'ers
1. Is 'leaving' not precise enough for you to do your job properly? (bearing in mind it may be procedural control on the odd occasion)
2. 'leaving' or 'left' both acceptable