Large Transport
Air Traffic Control Fully Certified
Air Traffic Control Time Certified In Pos 1 (yrs) 12.5
Communication Breakdown; Situational Awareness; Workload
ATC Issue All Types; Aircraft Equipment Problem Critical; Inflight Event / Encounter CFTT / CFIT
Air Traffic Control Issued New Clearance; Flight Crew Requested ATC Assistance / Clarification; Flight Crew Landed in Emergency Condition; Flight Crew Returned To Departure Airport; General Flight Cancelled / Delayed
Aircraft; Airspace Structure; Human Factors; Procedure
Aircraft Y had just departed IFR when Approach called us. Aircraft Y was returning VFR with an engine problem.  Aircraft Y was about 6 south of the airport at 1200 ft so I decided to [give them priority].  There was another [large transport aircraft] on one mile final Aircraft X on about a 12 mile final.  I called Approach and asked them to break out Aircraft X since he was still level at 2200 ft on the ILS.  I was trying to make a hole so Local West could land Aircraft Y on either runway.  About one minute later I found out that Aircraft X was already on Local West frequency.  I called Approach and asked them for a heading and altitude.  At this time Aircraft X had started to descend on the ILS but they were still above the MVA (Minimum Vectoring Altitude). There was training on Local West at the time and by the time that Aircraft X received the heading and altitude instructions they were below the MVA.  Aircraft X got as low as 1200 ft before the turn and climb started.  The two options were let Aircraft X land normally or issue the heading and altitude instructions before they got below the MVA.
BFI Tower controller reported a Local Control Trainee sent an aircraft around and issued instructions below the MVA.