Date: 201512
Local time of day: 0601-1200
Location: DEN.Airport, CO
Flight conditions: VMC
Light: Daylight
Aircraft: Medium Large Transport; Low Wing; 2 Turbojet Eng
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Initial Approach
Airspace: Class B DEN
ATC / advisory: TRACON D01
Aircraft component: MCP
Component problem: Improperly Operated
Reporter organization: Air Carrier
Reporter function: Pilot Not Flying; First Officer
Reporter qualification: Flight Crew Air Transport Pilot (ATP)
Human factors: Situational Awareness; Confusion; Time Pressure
Second reporter function: Pilot Flying; Captain
Anomaly: Deviation / Discrepancy - Procedural Published Material / Policy; Inflight Event / Encounter CFTT / CFIT
Detector: Person Air Traffic Control
When detected: In-flight
Result: Air Traffic Control Issued Advisory / Alert; Flight Crew FLC complied w / Automation / Advisory; Flight Crew Became Reoriented; Flight Crew Returned To Clearance
Contributing factors: Human Factors
Primary problem: Human Factors

Narrative: We had just come off of the ANCHR3 RNAV Arrival into Denver and were being vectored for a visual approach to 35R. Approach called out traffic to us and we followed them on the visual after we had been given a heading to intercept the 35R Localizer. When cleared for the visual approach; the Captain extended the centerline in the box off of FRONZ and set the altitude select window to the FRONZ altitude of 7000 ft. The Captain then began a fairly rapid descent to 7000 ft which caught me a little off guard since we were still quite a ways from FRONZ. However; it wasn't gross; just much more rapid of a descent than I was contemplating; since there was no hurry to descend. Approaching 7000 ft; ATC gave us an Altitude Alert and said 'check altitude; min altitude in this area 7500 ft.' During the descent; I was checking the approach plate to see if there were any obstacles; and noted a Tower at 6236 ft which was more than 500 ft below the altitude we were descending to (7000 ft). The Captain then climbed back to 7500 ft and continued the approach; the remainder of which was uneventful. After the flight; we discussed this and the Captain told me he had descended rapidly to correct for decaying airspeed vs pushing up the throttles. We thought perhaps ATC called us because of our rapid descent rate. My recollection was that we were just inside of DRUMM (14 DME fix on final) on the dogleg. The final had been extended off of FRONZ so the visual representation on the navigation display didn't show our location on the dogleg in relation to DRUMM which had an altitude of 9000 ft. I had previously put the runway on the Fix page; but didn't have that page up at the moment to see our distance from the runway. We were transferred to Tower freq and the rest of the approach was normal.While on a visual approach; extra caution should be exercised to ensure we don't descend too early. The Captain could have verbalized his intent to descend rapidly to correct for decaying airspeed; and I could have asked him about it. We should both have made sure we didn't descend early by crosschecking DME restrictions on the ILS; even though we were on a dogleg and cleared for the visual approach.


Second narrative: I was being vectored at 8000 ft MSL in VMC conditions and was given a 320 heading to intercept the 35R final approach course at DEN. I was five miles from FRONZ and called field in sight and was then cleared for a visual approach to 35R. I descended to 7000 ft which is the GSIA for FRONZ; and I was within a mile of the final approach course when ATC called with an Altitude Alert. He said I was below his minimum vectoring altitude of 7500 ft. I climbed back up to 7500 ft until I had VOR/LOC capture and then descended to cross FRONZ at 7000 ft. I received no other alerts; warnings or cautions from the EGPWS.


Synopsis: Air carrier First Officer reported being surprised when his Captain began a premature descent to 7;000 feet while being vectored towards FRONZ. ATC alerted the crew; now below the minimum vectoring altitude; so the Captain returned to 7;500 feet.