Air carrier flight crew reported clearance confusion by ATC resulted in a low altitude alert and a CFIT event.
Synopsis
Air carrier flight crew reported clearance confusion by ATC resulted in a low altitude alert and a CFIT event.
Narrative
On Day 0; I was Captain on Aircraft X ZZZ to JAC. JAC was landing north using Runway 01 and our filed flight plan had us filed to DNW; which is north of the airport. After passing CKW on the flight plan; we requested a descent to get lower as we did not expect to fly all the way to DNW. During our descent into JAC; we were cleared direct to the JOGOX intersection; while descending down to FL200. During our descent; we were cleared by ATC for the RNAV X Runway 01 approach into JAC. We were then given a descent to 13000 feet. We were level at 13000 feet with the Approach mode armed on the FMA with APP NAV showing. About 20 miles prior to JOGOX; the APPR mode captured FINAL APP and initiated a descent via the Multipurpose Control Display Unit (MCDU) profile. While level at 13;000 feet; the First Officer (FO) Pilot Flying (PF) had set 9;500 feet in the altitude window; which the altitude at the ZUGEN FAF. At 12;500 feet; ATC (Salt Lake Center XXX.XX) issued a low altitude alert and instructed us to climb to 13;000. The FO (PF) disconnected the autopilot and immediately climbed back up to 13;000 feet. ATC cleared us again for the RNAV X 01 approach with the restriction of crossing JOGOX at 13;000 feet. Before handing us off to JAC Tower; we were informed of a possible pilot deviation and given a phone number to call. After arriving at the gate; I called the number and spoke with someone. Discussing the issue after the call; my FO and I believe that there may have been either a frequency change or a Controller change between the two approach clearances. We believe that this may have led to the confusion regarding being cleared to descend via the approach. The weather was VMC the entire time and I had visual contact with the airport and surrounding terrain. Both pilots had their Terrain Displays active and at no time was any yellow or red terrain depictions observed.Cause: I would say that a causal factor could be that there is no hard" altitude at any of the IAF's for the approach. Being on a vector direct to JOGOX versus having a STAR procedure with a bottom altitude is also a factor. A "hard" altitude at the IAF's would be a way to trap this potential error.Suggestions: With no STAR for a descent profile; a "hard" altitude at the IAF's would be a way to trap this potential error."
Second reporter narrative
While operating Aircraft X from ZZZ to JAC on Day 0 we were instructed by Salt Lake Center to climb due to a low terrain warning on arrival decent into Jackson. I was the pilot flying during this leg. Jackson airport was landing 01 at the time. Our flight plan had a final fix before the airport as DNW. This fix is NW of the airport and is an unlikely fix for a Runway 01 landing. Due to the landing direction the Captain (CA) and I requested a lower altitude to compensate for the inevitable change of routing. We were given a decent to FL200 and direct to JOGOX for the RNAV X Runway 01. While in the decent to FL200 we were cleared down to 13000 and cleared for the RNAV X 01. The CA read back the clearance and I set 13000 ft. in the altitude selector. Once we leveled at 13000 ft. I began to slow the aircraft down to 210kts for the restriction at JOGOX; set 9500 in the altitude selector; and armed the approach. The aircraft intercepted the path and started a slow decent. Around 12500 ft. we received a transmission for Center about a low altitude alert and advised us to climb immediately. I disengaged the autopilot and started a climb to 13000 ft. The CA set the altitude selector to 13000 ft. and gave me a vertical speed climb. At the time the Controller issue a new clearance to cross JOGOX at 13000 ft. cleared for the RNAV X 01. I programmed 13000 ft. into the FMS for the requested crossing altitude at JOGOX; and rearmed the approach. Before our hand off to Tower the Center Controller advised us that there may have been a pilot deviation and gave us a number. We landed and taxied to the gate without incident in JAC. Once our post-flight duties were complete the CA called Center to discuss the situation. The weather was VFR and we had the airport in sight before the low altitude alert call from Center. At no time did we receive at aural alert about terrain or see anything other than green on our terrain displays. The CA and I think there may have been a Controller change or frequency change between the two approach clearances; but I am unable to recall with certainty. We are certain that we did not read back a crossing restriction on the first approach clearance we received. Cause: Miscommunication of intended ATC instructions. Non standard transition to the IAF of JOGOX charted at 11700 ft. Suggestions: I believe the approach clearance should have been given closer to the field. ATC gave us the initial clearance for the RNAV X 01 over 40 miles out over mountains terrain. If given the 13000 ft. direct to TUVOC it could elevate some of the misunderstanding and give more time for a decent.
Source: NASA Aviation Safety Reporting System (public domain). Reports are voluntary submissions and are not verified by NASA.