Date: 201605
Local time of day: 1201-1800
Location: TRK.Airport, CA
Flight conditions: Mixed
Weather elements / visibility: 10
Light: Daylight
Aircraft: Small Transport
Operator: Air Taxi
Operating under: Part 135
Flight plan: IFR
Mission: Passenger
Flight phase: Initial Approach
Airspace: Class E NCT
ATC / advisory: TRACON NCT
Reporter organization: Air Taxi
Reporter function: Captain; Pilot Not Flying
Reporter qualification: Flight Crew Instrument; Flight Crew Multiengine; Flight Crew Air Transport Pilot (ATP); Flight Crew Flight Engineer; Flight Crew Flight Instructor
Human factors: Confusion; Communication Breakdown
Anomaly: ATC Issue All Types; Deviation - Altitude Overshoot; Deviation / Discrepancy - Procedural Clearance
Detector: Person Air Traffic Control; Person Flight Crew
When detected: In-flight
Result: Air Traffic Control Issued Advisory / Alert; Flight Crew Became Reoriented; Flight Crew Requested ATC Assistance / Clarification
Contributing factors: Human Factors; Airport; Procedure
Primary problem: Human Factors

Narrative: We were told by Oakland Center to expect the RNAV 20 into KTRK; and were handed off to NORCAL TRACON for the approach who then cleared us to the IAF which included a hold course reversal. FO was PF for this leg. We were cleared at 11000 ft and also told to report when leaving the hold inbound on the approach. The FO inadvertently descended to 10700 ft while approaching the hold/IAF; I believe misinterpreting the approach plate; and I didn't catch it right away. ATC instructed us to climb to 11000 ft as previously cleared; which we complied with. Since we were just crossing the hold fix/IAF as we reached 11000 ft we then descended again to 10700; which is the hold altitude for the approach. Both the FO and I had interpreted the controller's earlier instructions to mean that we were being cleared for the approach and so thought we were complying with the approach hold altitude of 10700 ft. He then told us again to climb to 11000 ft; and I replied saying that we thought we were cleared for the approach and therefore were complying with the published altitude. His response was that he had not cleared us for anything other than the course reversal. We climbed immediately and continued past the hold fix on the approach course. Subsequently; we entered VMC; and then canceled IFR; whereupon we were given a frequency change and told to contact advisory.My take on this is that first; we did not hear the words 'cleared for approach;' and so my FO and I should have confirmed what we were to do after being cleared to the IAF but not cleared for the approach. I also see now that the controller's instructions were somewhat ambiguous; since he had instructed us to report leaving the hold inbound; and my response was that we would comply. I think that set us up to believe that we would fly the approach; including the published altitudes. I understand that is a mistake; but I think the controller could have told us to expect the clearance when passing the hold fix/IAF inbound; which would have confirmed that the 11000 ft clearance was meant for the hold also. This is especially true; in light of the fact that we were told by both Center and then NORCAL to expect the RNAV approach.As is often the case; a query of ATC might have helped to clear up my own confusion; and I will remember this in the future.




Synopsis: Air taxi Captain reported deviating from cleared altitude during approach procedures.