ZLC Controllers reported a clearance change that resulted in an aircraft entering a higher minimum IFR altitude than the aircraft was.
Synopsis
ZLC Controllers reported a clearance change that resulted in an aircraft entering a higher minimum IFR altitude than the aircraft was.
Narrative
Traffic was busy; sector was red on the NAS monitor. Numerous aircraft were climbing and descending and needed reroutes. Neither I nor the D-side noticed that Aircraft X was filed SABAT-QUERY at 130. He started flashing as he was several miles into the 133 terminal airspace. By the time I realized what was happening and that he wasn't on a transition route he was descending out of 135. I attempted to stop him at 133 but he descended down to 127 before he could correct. He subsequently climbed back to 133 and was cleared for the approach from QUERY. The controller I relieved said he received Aircraft X descending to 130 from sector 08 and didn't notice the error. The sector 08 controller said that Aircraft X was originally filed SABAT-WYS where 130 was a good altitude but he requested SABAT-QUERY and she was extremely busy without a D-side and not catch the error. Double check MVAs whenever an aircraft below 160 requests a route change. Hire enough staffing to have D-sides and split sectors where necessary.
Second reporter narrative
Aircraft X was issued a pilot discretion descent to 130 which would keep the aircraft above terrain but then requested a change in routing over QUERY which is in the next sector; Sector 06. I gave Aircraft X their requested routing of SABAT direct QUERY but was so busy I didn't think to check the MIA in sector 6's airspace; if I had I would have stopped the aircraft at 140. I was inundated with deviations; sequencing for Denver and had so many aircraft and no D-side. Request more staffing so that we can split sectors when needed and/or staff d sides.
Source: NASA Aviation Safety Reporting System (public domain). Reports are voluntary submissions and are not verified by NASA.