Bonanza 35
Air Traffic Control Fully Certified
Air Traffic Control Time Certified In Pos 1 (yrs) 7
Distraction; Time Pressure; Communication Breakdown
ATC Issue All Types; Airspace Violation All Types; Deviation / Discrepancy - Procedural Clearance; Deviation / Discrepancy - Procedural Published Material / Policy; Inflight Event / Encounter CFTT / CFIT
Air Traffic Control Issued Advisory / Alert; Air Traffic Control Issued New Clearance
Human Factors; Procedure; Airspace Structure
Weather broken at 3500 ft. at ZZZ. ZZZ FCT (Federal Contract Tower) advertising GPS-D approach; landing Runway XX. No air carriers will accept this approach. The only approach air carriers will accept to Runway XX is the RNAV/RNP (and most aren't authorized to). Aircraft Y on about 12 mile final for GPS-D approach to Runway XX.  Aircraft Z just coming on scope from north; direct ZZZZZ. Aircraft A just coming on scope from east; direct ZZZZZ. Both check on requesting approaches to Runway XY: Aircraft Z requesting the RNAV; Aircraft A requesting the ILS.  Aircraft Y on about a 10 mile final for Runway XX. I release Aircraft X off Runway XX on the [departure]. Aircraft X checks on out of 2500 ft.; without saying assigned altitude. I radar ID; and tell Aircraft X to climb and maintain 8000 ft. and continue on the [departure].  Coordinate Aircraft Z and Aircraft A opposite direction approaches. Tower says they have an Aircraft B departure off Runway XX first. I tell Aircraft X; reaching 3300 ft.; turn right heading 010; for traffic; in anticipation of releasing Aircraft B. I see Aircraft X make the turn about 3 miles off the departure end of Runway XX; out of 3100 ft.; which is within tolerance for mode C; and release Aircraft B. At this time; Aircraft X climb rate appears perfectly normal: 1900 ft. AGL 3 miles off the departure; there wasn't hot weather at [the airport] today; it was 19C on the hourly. Aircraft Y on about an 8 mile final; but  I notice that Aircraft Y is high (6000 ft.). Tower calls to say Aircraft B will now be after Aircraft Y ; because Aircraft Y needs to overfly and enter the downwind for descent. I start issuing holding instructions at ZZZZZ for Aircraft Z and Aircraft A. I've got Aircraft Z near ZZZZZ now; at 7000 ft. Aircraft A is still northeast of ZZZ; descending to 9000 ft.; since Aircraft X is climbing to 8000 ft. on a northbound vector. I go to put Aircraft X on a vector to intercept the airway; and see that they have only climbed 200 ft. in the last 5 miles; and were now below the MVA. I tell them to check altitude immediately and expedite climb. As soon as they are above the MVA; I give them climb vectors away from higher terrain. I eventually get them on the airway at 8000 ft. I took Aircraft X off the departure procedure when I put them on a vector; but they appeared to be climbing at a normal rate. If I'm going to take an aircraft off the departure procedure; I need to keep my scan more often on them and ensure they continue to climb appropriately. I could have boxed them around inside the 3300 ft. MVA; had I noticed they'd stopped their initial climb rate sooner. I had plenty of time; since Tower wasn't going to release Aircraft B until Aircraft Y landed. Had they continued to climb at the same rate; they should have been at least 5000 ft. in the 4200 ft. MVA (the location at which I noticed they were below the MVA). I am not sure why they reduced their climb rate so much. I should have been watching more carefully; but on that heading Aircraft X had 3+ miles to climb 900 ft.; and he'd just climbed 1900 ft. in the last 3-4 miles.
TRACON Controller reported a BE35 departure; at less than standard climb rate; falling below MVA.