Commercial Fixed Wing
Air Traffic Control Fully Certified
Air Traffic Control Time Certified In Pos 1 (yrs) 2
Communication Breakdown; Confusion
ATC Issue All Types; Deviation / Discrepancy - Procedural Published Material / Policy; Inflight Event / Encounter CFTT / CFIT
Air Traffic Control Issued New Clearance; Flight Crew Requested ATC Assistance / Clarification; Flight Crew Became Reoriented; Flight Crew Executed Go Around / Missed Approach; General Flight Cancelled / Delayed
Human Factors; Airspace Structure; Chart Or Publication
Aircraft X checked on level at 12000 ft direct CEGAN; the IAF for VOR/DME C approach. Aircraft X was told to cross CEGAN at or above 7800 ft which is the MVA at CEGAN but the altitude to maintain inside of CEGAN on the DME arc is 10000 ft. Aircraft X crossed CEGAN at approximately 11000 ft cleared for the approach. After Aircraft X crossed CEGAN at or above the altitude to maintain on the arc I expected him to fly the approach as he needed. Aircraft X descended below 10000 ft on the arc prior to fix BRKET but didn't set off any MSAW aural alerts. After crossing BRKET at approximately 8000 ft and turned onto the final approach course he reported a terrain alert and climbed to 11000 ft. Aircraft X was then vectored for the ILS RWY 14 approach and landed without incident.I don't feel there is a systemic issue to resolve with this event other than miscommunication or misunderstanding what the pilot is supposed to do on that approach after crossing CEGAN well above the published altitude regardless of what at or above altitude had been issued. I had expected him to level at 10000 ft until BRKET.
While conducting the VOR/DME-C approach to runway 32; we received an EGPWS terrain warning between BRKET and SERTE. The initial clearance from the center frequency was direct to CEGAN at 12000 ft after we requested the DME arc to runway 32 due to winds favoring 32. As we switched to Cascade approach; we were issued the clearance 'Cross CEGAN at or above 7800 ft; cleared VOR DME-C via the DME arc'. While I realized clearance altitude was lower than the published altitude on the DME arc from CEGAN to BRKET; we did not find it unusual to be issued a clearance lower than that of a published segment due to the use of minimum vectoring altitudes by air traffic controllers. We began a descent to 7800 ft and leveled at 7800 ft somewhere between CEGAN and BRKET. We then configured flaps 8 and slowed in order to ensure that the autopilot would successfully join the approach course. However as we began to approach BRKET I noticed that my MFD was showing 7500 ft as being the highest obstacle on our display. I grew concerned enough to begin reviewing the approach plate further and became concerned as the altitude on the approach between BRKET and SERTE should have been at least 8500 ft. I expressed my concern to my first officer and he quickly pointed out the existence of an obstacle on the approach plate at 7229 ft just prior to SERTE and requested I query approach regarding the obstacle. It was at the point that I began to query Cascade approach about the clearance issued. Cascade approach replied 'Say again'. At this point we received our first terrain caution aural announcement from the EGPWS. My first officer did an EXCELLENT job of immediately applying max thrust and calling for the spoilers to be retracted (they already were). We immediately began a climb to 11000 ft which we had decided during our brief as the highest MSA was 10700 ft. While climbing we advised Cascade approach of our intentions and that we had received a terrain warning. We then requested vectors to the ILS for 14 and took the performance penalty associated with landing with a tailwind.The primary cause of this incident was the clearance of 'Cross CEGAN at or above 7800 ft; cleared VOR DME-C via the DME arc'. Because it is common practice to issue altitudes lower than published altitudes on our approach we began a descent to 7800 ft despite the minimum altitude being 10000 ft on the approach plate. After post flight debriefing; my first officer and I could find no other interpretation to the clearance other than it was safe to descend to 7800 ft.I would suggest that in the future Cascade approach avoid the use of minimum vectoring altitudes while on a published approach and issue a crossing restriction of CEGAN at or above 10000 ft in compliance with the published altitudes on the approach plate.Additionally; I will ensure in the future to query any ATC assignments at altitudes lower than published segments on the approach plate. Even if assigned a lower altitude; in this case crossing CEGAN at or above 10000 ft and then SERTE at or above 8500 ft would have complied with the approach clearance and ensured compliance with minimum published altitudes on the approach plate.
EUG TRACON Controller and an Air Carrier flight crew reported that the aircraft received an GPWS warning while on approach due to a lower that standard altitude issued.