Narrative:

Flying a newly leased DHC6-200 on jump run level at 17400 ft MSL. ATC said we were at FL180 (class a airspace). I verified altimeter setting and altitude and determined my altitude encoder was off 600 ft. I switched to the #2 transponder which was within 200-300 ft.

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Original NASA ASRS Text

Title: A DHC6-200 SKYDIVING ACFT'S XPONDER MODE C READOUT READS 600 FT TOO HIGH WHILE IN PROX OF CLASS A AIRSPACE ON FREQ WITH D01, CO.

Narrative: FLYING A NEWLY LEASED DHC6-200 ON JUMP RUN LEVEL AT 17400 FT MSL. ATC SAID WE WERE AT FL180 (CLASS A AIRSPACE). I VERIFIED ALTIMETER SETTING AND ALT AND DETERMINED MY ALT ENCODER WAS OFF 600 FT. I SWITCHED TO THE #2 XPONDER WHICH WAS WITHIN 200-300 FT.

Data retrieved from NASA's ASRS site as of July 2007 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.