ATC showed small transport aircraft off assigned altitude. Faulty transponder altimeter encoder.

Attributes
ACN	316620
Time
Date	199509
Day	Thu
Local Time Of Day	1201 To 1800
Place
Locale Reference	atc facility : sax
State Reference	NY
Altitude	msl bound lower : 6000 msl bound upper : 6000
Environment
Flight Conditions	IMC
Light	Daylight
Aircraft 1
Controlling Facilities	tracon : n90
Operator	general aviation : personal
Make Model Name	Any Unknown or Unlisted Aircraft Manufacturer
Operating Under FAR Part	Part 91
Flight Phase	cruise other
Route In Use	enroute other
Flight Plan	IFR
Person 1
Affiliation	Other
Function	flight crew : captain oversight : pic
Qualification	pilot : instrument pilot : commercial pilot : cfi
Experience	flight time last 90 days : 120 flight time total : 1890 flight time type : 160
ASRS Report	316620
Person 2
Affiliation	Other
Function	flight crew : first officer
Events
Anomaly	aircraft equipment problem : less severe other anomaly other
Independent Detector	other controllera
Resolutory Action	flight crew : overcame equipment problem other
Consequence	Other
Supplementary
Primary Problem	Aircraft
Air Traffic Incident	other

Narrative:

Cleared to maintain 6000 ft. The controller stated a few mins later that he showed us at 6700 ft, and asked our current altitude which was 6000 ft. I recycled our transponder and asked what it was reading then. The reply was 6000 ft. The problem hasn't repeated itself since.

Original NASA ASRS Text

Title: ATC SHOWED SMT ACFT OFF ASSIGNED ALT. FAULTY XPONDER ALTIMETER ENCODER.

Narrative: CLRED TO MAINTAIN 6000 FT. THE CTLR STATED A FEW MINS LATER THAT HE SHOWED US AT 6700 FT, AND ASKED OUR CURRENT ALT WHICH WAS 6000 FT. I RECYCLED OUR XPONDER AND ASKED WHAT IT WAS READING THEN. THE REPLY WAS 6000 FT. THE PROB HASN'T REPEATED ITSELF SINCE.

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.