Date: 201509
Local time of day: 1201-1800
Location: N90.TRACON, NY
Flight conditions: VMC
Light: Daylight
Aircraft: PC-12
Operator: Air Taxi
Operating under: Part 135
Flight plan: IFR
Mission: Passenger
Flight phase: Descent
ATC / advisory: TRACON N90
Reporter organization: Air Taxi
Reporter function: Captain; Single Pilot
Reporter qualification: Flight Crew Flight Instructor; Flight Crew Air Transport Pilot (ATP); Flight Crew Instrument; Flight Crew Multiengine
Human factors: Confusion; Situational Awareness
Anomaly: Deviation - Altitude Excursion From Assigned Altitude; 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: I had descended to 5000 ft when I was handed off to the final controller. I checked in with the controller and told him I was at 5000 ft with the information and requested the Visual approach. The controller responding with descend to 4000 ft and turn to a heading. I didn't catch the heading so I responded with 'descend to 4000 ft and what was the heading?' The controller was very busy and began to talk to many other aircraft that were on the frequency. I reached for my vertical speed selector as I waited for the controller to call me back with the heading I was supposed to turn to. In my confusion; I never selected 4000 ft in my altitude selector. The frequency was congested and I was waiting for ATC to have a break long enough for me to clarify the heading I was assigned. I then noticed that my aircraft was at 4700 ft but my altitude selector was set to 5000 ft. Thinking that I descended below the altitude I was assigned; I turned off the auto pilot and climbed back to 5000 ft. The controller then called me and asks if I was descending to 4000 ft. I then began the descent to 4000 ft and responded with yes I'm descending to 4000 ft. The controller then tells me that he shows that I am at 5300 ft and I responded and said; I'm descending through 4800 ft for 4000 ft. It was then that I looked at my standby altimeter and it did show that I was at 5300 ft. When I was first told to descend to 4000 ft; Instead of pressing the vertical speed selector; I mistakenly pressed and held the baro selector. This switched my altimeter setting to standard when the altimeter setting was actually 30.35. Since I hadn't pre-selected 4000 ft when I was first given the descent; I thought that my aircraft was 300 ft below the altitude I was assigned so I corrected to the altitude I had set. But since the altimeter wasn't set correctly and I had not begun the descent; I actually climbed to 5300 ft. There are a number of factors that lead to this altitude deviation and they are all given in the description above. My standard practice is to always select the altitude I've been assigned prior to beginning a climb or descent. Today's situation caught me off guard from the time I first checked in with the controller. I let a very simple altitude and heading change confuse me which led to the mistakes made.




Synopsis: PC-12 pilot reported deviating from assigned altitude when he accidentally mis-set his altimeter.