Center controllers reported an aircraft on approach flew below the minimum IFR altitude when it deviated off course and descended below published altitudes.
Synopsis
Center controllers reported an aircraft on approach flew below the minimum IFR altitude when it deviated off course and descended below published altitudes.
Narrative
Sectors 3 and 4 were being split due to traffic count. During the briefing of splitting Sector 3 from 4 I was informed that Aircraft X was cleared over ZZZZZ for the RNAV XX into ZZZ and that he was going to shoot a missed approach and then fly the approach again for a full stop. The aircraft reaffirmed this during the briefing. After the split I noticed the aircraft was not on course with RNAV XX but appeared to be going direct to the wrong fix. I confirmed with the controller that initially cleared the aircraft what the clearance was and then questioned the aircraft. I cleared the aircraft directly to ZZZZZ1 to cross at 13000 ft. and then begin the RNAV XX approach. Moments later I noticed the aircraft descending down to a lower altitude in a 13000 ft. MIA (Minimum IFR Altitude); I issued a low altitude alert and restated the aircraft's clearance. I then finished the briefing to give the sector to a different controller.The main factor to this incident was the pilot's error. However; other contributing factors were poor staffing and poor timing. Management has to juggle unsafe staffing levels with unsafe traffic congestion. The supervisor was balancing this as best as possible; but I was still paged back in order to split a sector from a training team to try and stay ahead of a red sector because the staffing is poor. The staffing is poor because the facility staffing number is wrong. Nobody is willing to address or change the staffing number. While I know everywhere is low staffed; the number of controllers required to staff a facility is a calculable number and it is wrong. Even if we were at this facility's staffing goal we would still be short.
Second reporter narrative
As I was taking over the sector; Aircraft X had already been cleared for the approach over ZZZZZ. During the briefing the aircraft flew from ZZZ toward ZZZZZ1; which is an IAF that starts from the west. The aircraft had filed that. The controller restated the aircraft was cleared present position direct ZZZZZ; and to maintain 13000 ft. until ZZZZZ cleared approach. The controller noticed the aircraft descending out of 12800 ft. while in a 13000 ft. MIA (Minimum IFR Altitude). The controller issued a low altitude alert and told the aircraft to maintain 13000 ft. The aircraft responded and climbed back up. At that point I took over the sector. I observed the aircraft make a 180-degree turn; maybe 6 miles south of ZZZZZ; rather than flying over the fix and doing a procedure turn. I changed him to advisories and told him to call me on the missed approach. At this point I decided that this pilot needed to call us to have a conversation about what he was thinking/doing. When he came back on the frequency I issued him a brasher warning and advised my supervisor of the situation. ZZZ is a high altitude; short runway in the middle of the mountains. It was never designed to accommodate the traffic that goes in to it. The airport needs to be moved and redesigned. Good luck with that.
Source: NASA Aviation Safety Reporting System (public domain). Reports are voluntary submissions and are not verified by NASA.