Date: 201702
Local time of day: 1201-1800
Location: SJC.Airport, CA
Flight conditions: IMC
Weather elements / visibility: 7
Light: Dusk
Aircraft: B737 Undifferentiated or Other Model
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Initial Approach
Airspace: Class E NCT
ATC / advisory: TRACON NCT
Reporter organization: Air Carrier
Reporter function: Captain; Pilot Not Flying
Reporter qualification: Flight Crew Air Transport Pilot (ATP)
Human factors: Situational Awareness; Workload
Second reporter function: Pilot Flying; First Officer
Anomaly: ATC Issue All Types; Deviation - Altitude Overshoot; Deviation / Discrepancy - Procedural Clearance
Detector: Person Flight Crew
When detected: In-flight
Result: Flight Crew Became Reoriented; Flight Crew Returned To Clearance
Contributing factors: Human Factors
Primary problem: Human Factors

Narrative: ATC threw us many late and revised clearances to our arrival/landing runway; with vectors; speed; and altitude changes. Somewhere in the many changes; aircraft automation changed to CWS (Control Wheel Steering) Pitch. We had finally cleared up a confusing clearance by ATC (bottom line was to descend to 7000; then via the remainder of the SILCN 4 RNAV Arrival). The change to CWS Pitch was noted and verbalized by the PM at around 7400 MSL; but obviously not clear enough to register with the PF. After another radio call and coordination in the cockpit; the PM clearly verbalized to the PF that the aircraft had descended to around 6600/6700 ft. The PF made a correction and we leveled at 7000. ATC did not say anything; and I do not believe there was any conflict with other traffic.I just completed AQP (Advanced Qualification Program) in January and credit that with helping trap the error. The emphasis on terrain awareness; distraction management; and to slow down was exactly the situation we found ourselves in. I firmly believe our current training is exactly what is needed to raise awareness. While this did seem like an exaggerated case of distractions; it is what it is; and we need to deal with it. Distractions; both internal and external; can diminish communication; and I (we) need to be more aware of that dynamic.


Second narrative: I was the Pilot Flying; the Captain was the Pilot Monitoring. We were cleared to descend via SILCN 4 Arrival landing 30L. 4000 ft was selected. The aircraft was in VNAV PATH. I previously briefed ILS 30L but then remembered a note on the weather coversheet that strongly suggested RNP Z 30L. So I reloaded the approach and briefed while still early in the descent. Somewhere around VLLEY; ATC informed us that they were switching the airport to a 12 arrival due to changing winds. We were immediately turned to an east heading. I quickly reloaded ILS 12R and briefed. ATIS was still broadcasting 30L. Captain had to ask numerous times for current weather conditions but to no avail. ATC said to expect a direct GGUGL intersection to rejoin the SILCN 4 and plan the RNP Z 12R. So this was our fourth Approach Brief in less than ten minutes. To say we were busy is an understatement. While Captain was trying to get weather ATC directed us direct GGUGL and to descend to 8000. I selected GGUGL; selected LNAV and verified VNAV and 8000 was in the altitude window. Captain came back; still no new weather. Captain asked me; 'Are we to cross GGUGL at 8000 or as published which is between 7000 and 8000'? I wasn't sure so he asked ATC and they said to cross GGUGL at 7000. I selected 7000 in the altitude window and thought I put the aircraft back in VNAV. We were cleared for the RNP upon reaching HITIR. Captain pleaded for at least new wind report so we could plan our landing speeds. The aircraft; which was; I am estimating; a mile or two south of GGUGL and descending; continued to descend below 7000 ft; which I did not catch. At approximately 6600 ft; the Captain asked; 'Aren't we supposed to be at 7000 ft?' I agreed and immediately selected Vertical Speed; stopped the descent; and started to climb back to 7000 ft. I noticed at this point we must have fallen out of VNAV for reasons I do not know. I recruised at 7000 ft; 210 knots; which put the aircraft in LNAV/VNAV PATH. We executed the RNP 12R; which they then ironically switched the Runway to 12L once on final. So in the last 15 minutes of flight we had 5 different Approach Briefings and two arrival changes. Crew coordination was exceptional; just overloaded. Preventative Measures: Hard to say; Captain and I were communicating perfectly; it was just a matter of too much programming and too many changes. If we knew weather had been available before the airport swapped runways; Captain would have had one less task and we might have avoided what happened. ATC was working well with the situation and it seemed he was a little overloaded task-wise as well. He was doing a great job as he had numerous aircraft he had to reroute for a south landing.


Synopsis: B737 flight crew reported overshooting the assigned altitude on descent into SJC citing high workload and a lack of FMC mode awareness as contributing.