Super King Air 200
Air Traffic Control Fully Certified
Air Traffic Control Time Certified In Pos 1 (yrs) 6
Communication Breakdown; Situational Awareness; Confusion
ATC Issue All Types; Deviation - Altitude Undershoot; Deviation / Discrepancy - Procedural Clearance; Deviation / Discrepancy - Procedural Published Material / Policy; Inflight Event / Encounter CFTT / CFIT
Air Traffic Control Issued New Clearance
Human Factors
Working clearance delivery. Very slow on Thanksgiving. Aircraft X called up for an IFR to SFF (Felts Field; WA). Gave him the IFR clearance with 'fly runway heading; maintain 160.' He read back 'fly runway heading; up to 60.' I totally missed the read back. Tower departed him and changed to Departure. Aircraft X reported on with radar climbing to 60; but radar missed the altitude also....he assumed 160 too. Aircraft x told radar they were 'level at 60' in a 6;500 MVA.  Supervisor told me about it about an hour later after he reviewed the tapes.Talk about expectation bias! I didn't listen completely to his read back. I wasn't preoccupied; and I wasn't busy; just missed the altitude read back. I think the pilots read back of 'fly runway heading; up to 6 thousand' might have sounded a little bit like 'one six thousand' but it's no excuse. I didn't catch the wrong read back and it was a perfect 'Swiss cheese' model we've been talking about for the last 15 or more years!More vigilance!Less distraction!Focus on the pilots' read back and just don't assume it's going to be correct!
BOI Clearance Delivery Controller did not catch an incorrect read back which caused an aircraft to level off in a higher MVA [Minimum Vectoring Altitude]; below the MVA altitude.