Date: 201906
Local time of day: 0001-0600
Location: ZZZ.ARTCC, US
Aircraft: Medium Transport; Low Wing; 2 Turbojet Eng
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Cruise
Airspace: Class E ZZZ
ATC / advisory: Center ZZZ
Second aircraft: Large Transport; Low Wing; 2 Turbojet Eng
Reporter organization: Government
Reporter function: Instructor; Enroute; Approach
Reporter qualification: Air Traffic Control Fully Certified
Human factors: Training / Qualification; Situational Awareness; Confusion
Anomaly: ATC Issue All Types; Conflict Airborne Conflict; Inflight Event / Encounter CFTT / CFIT
Detector: Person Air Traffic Control
When detected: In-flight
Result: Air Traffic Control Separated Traffic; Air Traffic Control Issued New Clearance; Flight Crew Requested ATC Assistance / Clarification
Contributing factors: Human Factors; Company Policy; Airspace Structure
Primary problem: Human Factors

Narrative: This event occurred during a skill check. The supervisor is not certified on the position; and I was the CPC plugged in with the trainee. The trainee had Aircraft X on the right downwind for ILS-X at 040. Aircraft Y was on the opposing base descending to 030 but with adequate space to put Aircraft X in front. The trainee turned Aircraft X heading 320 and descended to 035 (the lowest the MVA would allow). This was an inadequate base turn and aimed him towards Aircraft Y; although there was still adequate space for the sequence to work. The trainee gave a late turn-on clearance for the ILS-X to Aircraft X and gave the wrong call sign; so Aircraft X did not respond to the clearance. There was still adequate space for the sequence to work; but as Aircraft X was crossing the localizer northwest bound the trainee issued an ILS clearance with a heading of 050 to intercept (this was not going to intercept). The pilot read back reluctantly but didn't immediately turn because the clearance did not make sense with an incongruent intercept angle. As Aircraft X was not yet turning; separation was becoming an issue. The supervisor called attention to the situation and said; 'Do something.'  Had Aircraft X immediately accepted the clearance that did not make sense and at least turned to the 050 heading; lateral separation would have been maintained and diverging courses would have existed.  When told to do something the trainee stuttered a couple times and then turned Aircraft X heading 040.  I took over and turned Aircraft Y right; heading 280 and eventually heading 030; effectively spinning him. This increased separation which may have already decreased to less than standard; but had allowed Aircraft Y to briefly spill into a 040 MVA.As the 'Safety' controller plugged in for the skill check; I had avoided input as much as possible.  I had delayed for too long; however; and allowed the trainee to paint himself into a corner.  The situation reached a point where there was no good solution. I may have traded an MVA violation for a LOSS [Lack Of Standard Separation]. On the other hand; the LOSS may have already happened. It was close to 3 miles.I know that as the Certified Professional Controller [CPC]; I was responsible for the position.  Frequently I observe a CPC telling the trainee what to do; and asking questions during a skills check with a supervisor who's not certified. This was what I was trying to avoid.  Ultimately my reservations led me to wait too long to correct the problem.Although everyone knows; or ought to know his role in this type of skill check scenario; it would serve the facility well to brief or pre-brief the session on roles; responsibilities; expectations.




Synopsis: Center Controller reported observing a trainee receiving a skills check from a Supervisor vector an aircraft through the final approach course; below the Minimum Vectoring Altitude and possibly into a loss of separation with another aircraft.