Date: 202008
Local time of day: 1201-1800
Location: PDX.Airport, OR
Flight conditions: VMC
Light: Daylight
Aircraft: Commercial Fixed Wing
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Flight phase: Descent
Airspace: Class C PDX
ATC / advisory: TRACON P80
Reporter organization: Air Carrier
Reporter function: First Officer; Pilot Flying
Reporter qualification: Flight Crew Multiengine; Flight Crew Instrument; Flight Crew Air Transport Pilot (ATP)
Human factors: Confusion; Situational Awareness; Communication Breakdown
Second reporter function: Pilot Not Flying; Captain
Anomaly: ATC Issue All Types; Deviation - Altitude Excursion From Assigned Altitude; Deviation / Discrepancy - Procedural Clearance
Detector: Person Air Traffic Control
When detected: In-flight
Result: Air Traffic Control Issued New Clearance
Contributing factors: Human Factors
Primary problem: Human Factors

Narrative: On arrival into PDX we were with Approach Control; who give us direct to the OMMSI fix; off the arrival and toward an approach fix. He then gave us; as I best recall; descend to 2;500 ft. We descended. He then; at just passing 4;000 ft; communicated in a flustered way to verify we have terrain in sight and to stop our descent. Or slow it; I really wasn't sure the meaning behind this communication; as we were descending; in perfectly clear daytime and have zero warnings. Our radar altimeter has not even populated which means we were 2;500+ feet above any terrain and we had all terrain and the airport in sight.He clarified to us our last clearance received. He thought it was 5;300 ft. We could not exactly verify that as I had adjusted the altitude window to higher than 2;500 ft to stop a descent; but it was definitely not 5;300 ft assigned. Had we continued closer on our way towards 2;500 ft I'm sure we would have questioned things as well. He noticed an error from alerts on his end I'm sure; and we were on our way to noticing incorrect happenings; also. If anything; this was just a pure accidental clearance given earlier than planned. We may have been off the vertical safety course for a bit but this sort of accidental clearance issuance is more based in being human than gross negligence. I suppose briefing more MSA (Minimum Safe Altitude) in relation to position of approaches/arrivals could be useful; but it was clear and I routinely get clearances to descend lower than other IFR segments on approach courses. I don't know what else to say really. He caught himself and checked we were seeing what we were doing. Good.


Second narrative: FO (First Officer) was flying. We were taken off the arrival and cleared direct to a fix on the approach. Then given a further descent to 2;500 ft. I read back 2;500 ft about 4;000 ft; Approach in a panicked voice asked if we saw the field; which I replied affirmative. He then cleared us for the visual and asked us to arrest our descent and if we see the terrain. I said we did. He said our clearance was only to 5;300 ft and he asked again if we saw the terrain. I replied we did and were Visual to 28R. There were no terrain warnings in the cockpit; nor was the RA (Resolution Advisory) registering terrain at that time. We didn't feel there was a threat to the aircraft and landed uneventfully on 28R. When Approach cleared us to 2;500 ft and I read back 2;500 ft is when the error should have been caught.


Synopsis: Air carrier flight crew received erroneous descent clearance inflight from Air Traffic Control.