Date: 202005
Local time of day: 1201-1800
Location: D01.TRACON, CO
Flight conditions: Mixed
Weather elements / visibility: 10
Light: Dusk
Aircraft: B737-700
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Initial Approach
Airspace: Class B DEN
ATC / advisory: TRACON D01
Reporter organization: Air Carrier
Reporter function: Pilot Flying; First Officer
Reporter qualification: Flight Crew Multiengine; Flight Crew Instrument; Flight Crew Air Transport Pilot (ATP)
Human factors: Communication Breakdown; Confusion
Second reporter function: Captain; Pilot Not Flying
Anomaly: ATC Issue All Types; Inflight Event / Encounter CFTT / CFIT
Detector: Person Air Traffic Control; Person Flight Crew
When detected: In-flight
Result: Air Traffic Control Issued Advisory / Alert; Air Traffic Control Issued New Clearance; Flight Crew Requested ATC Assistance / Clarification
Contributing factors: Airspace Structure; Human Factors; Procedure
Primary problem: Procedure

Narrative: While descending on the RNAV Arrival; Approach gave us a clearance to descend to 11;000 ft. and airspeed was our discretion. At this point on the approach; it was VFR. We were on a right downwind with the airport and preceding aircraft on a base leg in sight. Approach Control instructed us to slow to 190 kts. and then descend to 7;000 ft. I pulled the speedbrake lever and dialed in 7;000 ft. There was a cloud layer just north of the field; but at this point; both the Captain and I had the other traffic in sight. As we were coming through about 7;500 ft.; Approach instructed us to slow to 150 kts.; turn to a heading of 040; and descend to 6;000 ft. This all happened very quickly and the expectation bias was that we were going to keep the approach tight with the other aircraft and follow them in. As the other aircraft turned base to final; they lost sight of the runway because of the cloud layer just north of the field. Approach asked us if we still had the traffic aircraft in sight. At that point. the other aircraft was well inside the cloud layer so we did not. Approach gave us instructions to turn to a heading of 140 to intercept the ILS course. As we were coming through about 6;600 ft. Approach told us to maintain 7;000 ft. and said that the MVA(Minimum Vectoring Altitude) for that sector was 7;000 ft. We leveled off and climbed back to 7;000 ft.; and intercepted the ILS course on the 140 heading.


Second narrative: Descending on right base and cleared to 7;000 ft. ATC asked if we had the preceding B737 from north in sight. There were clouds in his vicinity; but I did not anticipate he would need to descend into clouds. Our flight path for base; dogleg; and final was clear of clouds with runway in sight. When asked; I told ATC we had preceding aircraft and runway in sight. We were cleared to follow the preceding traffic for a Visual Approach. We both understood clearance to 6;000 ft. However I was unable to query because the preceding traffic then began communication with approach that he was temporarily IMC and there were several communications regarding the tops and bottoms of the clouds.During this; the Pilot Flying was continuing his descent to 6;000 ft. ATC asked if we had traffic in sight. We had lost it behind clouds but the runway was still in sight for us. We were at 6;600 ft. descending when ATC then asked us to climb back to 7;000 ft. to his MVA (Minimum Vectoring Altitude) and went ahead and gave us a vector to intercept the ILS. We had runway in sight; but I suspect he was preemptively providing ILS in case we also became IMC. We may very well have missed the correct altitude clearance thinking we were cleared to 6;000 ft. vice 7;000 ft. or ATC may have just preemptively wanted us back up to MVA. I'm not sure at this point. Also; there was never any traffic or spacing issues during his event as the closest TCAS ever showed us to leading traffic was approximately 5.5 miles.


Synopsis: B737 flight crew reported after descending to the altitude assigned by ATC; they were told to climb back to their previous altitude because they were below the Minimum Vectoring Altitude.