Date: 201301
Local time of day: 0601-1200
Location: DEN.Airport, CO
Flight conditions: Mixed
Weather elements / visibility: Fog
Light: Daylight
Aircraft: B737-700
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Flight phase: Initial Approach
Airspace: Class B DEN
ATC / advisory: Tower DEN
Aircraft component: FMS/FMC
Component problem: Design
Reporter organization: Air Carrier
Reporter function: Captain
Reporter qualification: Flight Crew Air Transport Pilot (ATP)
Human factors: Confusion; Distraction; Workload
Anomaly: ATC Issue All Types; Aircraft Equipment Problem Less Severe; Deviation / Discrepancy - Procedural FAR; Inflight Event / Encounter Weather / Turbulence
Detector: Person Flight Crew; Person Air Traffic Control
When detected: In-flight
Result: Air Traffic Control Issued New Clearance; Flight Crew Requested ATC Assistance / Clarification
Contributing factors: Airport; Human Factors; Procedure; Weather
Primary problem: Weather

Narrative: I am filing this report to point out an extremely challenging arrival and approach. Initially cleared for PURRL RNAV STAR to DEN; we set up for Runway 35R since they didn't give us a runway and we had used 35R on an earlier trip. We briefed the arrival and approach to 35R and then had following changes:1) Slow to 250 from published 280.2) Given Runway 35L (changed box and briefed).3) Given ZPLYN1 Arrival and 35L (changed box and briefed).4) Told to accelerate to 280.5) Switched controllers and told to hold 210.Several of these changes required total [reprogramming of our route on the FMS]. Still a ways out the RVR dropped to 1;400 for blowing fog. The minimums for our CAT I aircraft (no HUD) were RVR 1;800. However; we had had 35R in sight for 40 miles so we asked for a visual to 35R with the field in sight. Approach Control said he couldn't do it because the field was IFR; but he gave us a heading and cleared us for the ILS 35R. (We were way out as all this was happening.) He said RVR for 35R was 2500/6000/6000. Tower then recleared us to land 35R. We flew the ILS 35R as previously briefed to an uneventful visual landing. As we cleared the runway; Tower told the guy behind us RVR has dropped to 1;400 approach end. He said he needed 1;800 and Tower said to wait as it just came up to 1;800 and then quickly to 6;000. My concern is whether we had the reported visibility required for the ILS even though we were visual the whole way. My First Officer said Tower told us RVR was 2500/6000/6000. He did not file a report because he is sure of this and is positive we stayed within the rules.I don't like the new RNAV arrivals that are very complex. It takes a long time to load and check them. The many restrictions--accompanied by numerous airspeed; arrival and runway changes--make them extremely challenging. We commented that they should attach a company safety form to the flight plan. Tower and Approach Control guys were very helpful.




Synopsis: Great coordination between ATC and the flight crew of a B737-700 salvaged an uneventful landing at DEN during rapidly changing airport weather due to blowing fog. Programming changes to complex RNAV STARs was cited as a contributing factor to the flight crew's workload.