Air Traffic Control Fully Certified
Distraction; Communication Breakdown
Deviation - Track / Heading All Types; Deviation / Discrepancy - Procedural Published Material / Policy; Inflight Event / Encounter CFTT / CFIT
Air Traffic Control Issued Advisory / Alert; Air Traffic Control Issued New Clearance; Flight Crew Returned To Clearance
Human Factors
Aircraft X had been issued direct to CABYA for the RNAV 6 approach into 0A9. The aircraft had been tracking direct to the fix for approximately 30 miles before I cleared the aircraft to cross CABYA at 5;300 and advised he was cleared for the approach. The aircraft was well clear of terrain at his altitude and direct to CABYA. I go on and do a couple of other position related tasks and notice Aircraft X well south of course about to enter 6;700 MVA. I issued the aircraft a turn to 360 to clear the aircraft of the MVA. The aircraft may have entered the 6;700 MVA; but was quickly clear of the MVA as I had caught it just as he was about to enter the higher MVA. Once I got the aircraft clear of the terrain I asked why he had gone off course. The aircraft told me he was just setting himself up to be straight in outside of CABYA. I advised the aircraft that if he has been cleared direct a fix that he has to navigate direct the fix and if he wants other routing he needs to let me know in advance and I can set them up to be above the MVA. The pilot acknowledged. I should have noticed the southern turn of the aircraft before I did. I had assumed the aircraft who had been tracking for 30 miles direct the fix would still be direct the fix.
TRI TRACON Controller reported a small transport tracked off assigned route; entering higher MVA.