Narrative:

While preparing for GPS runway 24 at hky; setting up GPS for approach; aircraft on autoplt and power reduced to decelerate; aircraft descended from 3400 ft initial altitude. No audio alert; no disconnect. ATC called and asked my altitude. At that time I noted altitude below initial altitude. ATC advised me to climb back to 3400 ft and I did. This was the second attempt at this approach; the first was missed because of GPS interface problems I failed to identify. 2ND approach was successful. ATC absolutly saved my day with the call. My lack of familiarity with installed GPS; major distraction and encroaching WX; level 3 cell; almost overcame my abilities.

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Original NASA ASRS Text

Title: LACK OF FAMILIARITY WITH GPS NAV SYSTEM CONTRIBUTES TO MISSED APCH; ALT DEV AND WORK OVERLOAD FOR SINGLE PLT OF PA31 ATTEMPTING GPS APCH IN INCLEMENT WX.

Narrative: WHILE PREPARING FOR GPS RWY 24 AT HKY; SETTING UP GPS FOR APCH; ACFT ON AUTOPLT AND POWER REDUCED TO DECELERATE; ACFT DSNDED FROM 3400 FT INITIAL ALT. NO AUDIO ALERT; NO DISCONNECT. ATC CALLED AND ASKED MY ALT. AT THAT TIME I NOTED ALT BELOW INITIAL ALT. ATC ADVISED ME TO CLB BACK TO 3400 FT AND I DID. THIS WAS THE SECOND ATTEMPT AT THIS APCH; THE FIRST WAS MISSED BECAUSE OF GPS INTERFACE PROBS I FAILED TO IDENTIFY. 2ND APCH WAS SUCCESSFUL. ATC ABSOLUTLY SAVED MY DAY WITH THE CALL. MY LACK OF FAMILIARITY WITH INSTALLED GPS; MAJOR DISTRACTION AND ENCROACHING WX; LEVEL 3 CELL; ALMOST OVERCAME MY ABILITIES.

Data retrieved from NASA's ASRS site as of January 2009 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.