Learjet 31
Air Traffic Control Developmental
Communication Breakdown
ATC Issue All Types; Deviation / Discrepancy - Procedural Clearance
General None Reported / Taken
Procedure; Human Factors
Air Carrier X was arriving from the East and was given a descent clearance; pilot's discretion (PD); to 080 due to the MVA at 080 East. As Air Carrier X was leaving 100 I advised the pilot to expect lower in 7 miles to which he replied 'Will do'. A minute later I noticed that Air Carrier X was at 078 and approximately 2 to 3 miles East of the 080 MVA boundary line. I then advised Air Carrier X to check his altimeter and advised him that our altimeter was 29.36 to which he replied 'Roger'. I then noted his altitude readout continued down to 076 and then back up to 078; which by that point he was clear of the 080 MVA. I then gave him a descent clearance to 030. Ensure that the pilot understood that he was to maintain 080; and to expect lower in 7 miles. I feel by the way that he had replied to me; that he might have thought that I had given him further clearance down to 080.
TRACON Controller issued an 'expect' clearance for a lower altitude only to witness the aircraft in question begin a descent.