Date: 201602
Local time of day: 0601-1200
Location: SJC.Airport, CA
Flight conditions: IMC
Weather elements / visibility: Fog
Light: Daylight
Aircraft: Small Transport
Operator: Personal
Operating under: Part 91
Flight plan: IFR
Mission: Personal
Flight phase: Final Approach
Airspace: Class C SJC
ATC / advisory: Tower SJC
Reporter organization: Personal
Reporter function: Pilot Flying; Single Pilot
Reporter qualification: Flight Crew Instrument
Human factors: Human-Machine Interface; Distraction; Situational Awareness
Anomaly: ATC Issue All Types; Deviation / Discrepancy - Procedural FAR; Deviation / Discrepancy - Procedural Clearance; Deviation / Discrepancy - Procedural Published Material / Policy; Inflight Event / Encounter Weather / Turbulence
Detector: Person Flight Crew
When detected: In-flight
Result: Flight Crew Returned To Clearance
Contributing factors: Human Factors; Weather; Procedure
Primary problem: Weather

Narrative: I obtained the ATIS for landing in San Jose when I was at least 20 miles out; and ATIS said cleared for the visual landing 30L. As I approached the KLIDE intersection I could clearly see the city of San Jose and I could see the outline of the airport beyond. ATC made me vector around somewhat for spacing; and then I was cleared for the visual. The city of San Jose was so clearly in view below me. As I was taught despite being cleared for the visual; I set up and flew the RNAV GPS Y for 30L. I past the FAF of HIVAK; and I was perfectly on the glide slope and glide path. However; I looked up from the instruments to see that the airport had unexpectedly become obscured by a fog bank that had moved in. I was surprised that the runway environment had become obscured; but I was precisely on the approach. I proceeded further and heard another pilot report breaking out at 300 feet. Indeed; I broke out at 350 feet and landed perfectly.This was a perfectly executed instrument approach; but the rub is that I was cleared for the visual....not the instrument approach. Even though I was really quite safe being on the glide slope and glide path; I should have told the tower that I needed to be cleared for the RNAV Y for 30L. That was my error. I was so consumed with flying the instrument approach that I technically violated the clearance. I really was not in danger or unsafe at any time; but the rules are the rules. The FAR/AIM says that the visual clearance is clearly a visual approach. Perhaps the fact that I was perfectly on the glide slope and glide path and landed perfectly made the tower overlook the violation of the clearance. Still; it was a violation; and it shall not happen again. It was just that the fog bank moved in after I had received the clearance; and it all happened so fast. Further; I was lulled into ignoring the nature of the clearance as I was really flying the instrument approach per my training. It is a learning experience that the approach happens so fast; and instrument flying demands that the pilot focus on the instruments; not the visual. In this case of the fog bank unexpectedly moving in to cover the airport; I got 'caught'.




Synopsis: Pilot reported of being cleared for a visual approach. Pilot set up instruments to follow the glideslope; when finished he looked up and was in the clouds. Pilot flew an instrument approach despite being cleared for the visual.