TBM 700/TBM 850
Flight Crew Commercial; Flight Crew Instrument
Flight Crew Last 90 Days 18; Flight Crew Total 7200; Flight Crew Type 475
Confusion; Human-Machine Interface
Aircraft Equipment Problem Less Severe; Deviation - Altitude Undershoot; Deviation / Discrepancy - Procedural Published Material / Policy; Deviation / Discrepancy - Procedural Clearance
Air Traffic Control Issued Advisory / Alert; Aircraft Automation Overrode Flight Crew; Flight Crew Returned To Clearance; Flight Crew Became Reoriented
Aircraft; Human Factors
I was level at FL190 after a series of step downs from FL250.  I was told by ATC to descend to 15;000 feet.  I pressed and held the VS (Vertical Speed) button on my Garmin G600 bezel to activate the VS mode and initiate a descent.  The VS had been previously set to minus 1200 FPM.  The aircraft pitched over as expected and began to descend.  I then pressed the ALT button on the G600 and set in 15;000 feet; my assigned new altitude. I then realized that the Controller had not given me the required altimeter setting; since I was descending out of the flight levels.  I requested the current altimeter setting and was given 30.08.  I then pressed the Baro button on the G600.  When I turned the knob clockwise to go from 29.92 to 30.08; the numbers did not change in the baro window. I then pressed Baro again; and set in the correct altimeter setting for the descent to 15;000 feet. A few minutes later ATC called and asked me to descend to 15;000 and that I was in a shallow climb.  I looked at the VSI and saw that I was climbing about 400 FPM and was at about FL200. I immediately engaged CWS and began a descent.  Of course; I was puzzled that I had been climbing and not descending at 1;200 FPM. I ascertained that when I pressed Baro the first time; I had inadvertently pressed the adjacent VS button.  The clockwise turn of the control knob on the G600 caused the VS rate to go from minus 1;200 FPM to positive 400 FPM; with the resulting altitude excursion. I should have realized that something was amiss when the baro window did not change as I attempted to set it.  In the G600; whichever button is pressed momentarily will result in that parameter being changed as the knob is turned.  In this case it was the VS; which caused the VS to become positive. My normal flow of initiating the descent; entering the new baro; and then setting the target altitude was disrupted in this case.  However; I should have noticed that I was climbing and corrected the problem; a perfect example of too much dependence on automation. Contributing to this situation is the G600 user interface of using buttons and single control knob to set the parameter to be changed.
TBM pilot reports inadvertently selecting vertical speed on his G600 while attempting to set QNH during descent; resulting in an undetected climb. ATC notices however and the error is corrected.