ARTCC altitude readout different than being flown. Aircraft system checked and found correct.

Attributes
ACN	478150
Time
Date	200006
Day	Fri
Local Time Of Day	1201 To 1800
Place
State Reference	VA
Altitude	msl single value : 5500
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : zdc.artcc
Operator	general aviation : personal
Make Model Name	Commander 112A
Operating Under FAR Part	Part 91
Flight Phase	cruise : level
Route In Use	enroute : direct
Flight Plan	VFR
Person 1
Affiliation	other
Function	flight crew : single pilot
Qualification	pilot : private
Experience	flight time last 90 days : 15 flight time total : 600 flight time type : 480
ASRS Report	478150
Person 2
Affiliation	government : faa
Function	controller : radar
Qualification	controller : radar
Events
Anomaly	non adherence : far non adherence : published procedure
Independent Detector	atc equipment other atc equipment : alt aiert other controllerb other flight crewa
Resolutory Action	controller : issued advisory
Consequence	other
Supplementary
Problem Areas	Flight Crew Human Performance ATC Facility ATC Human Performance Aircraft
Primary Problem	Ambiguous

Narrative:

While contacting ZBW for flight following (with the correct altimeter setting) was informed by the controller that his equipment showed us at 300 ft high. We acknowledged his transmission. Split the difference between readout and actual altitude. No other controller had noted a problem prior to this controller. In thinking about this later, I should have stayed at the correct altitude. On reaching home airport, have asked the local repair shop to check the encoder. Have not had a report back nor have we used the aircraft. We also check the logs, the encoder was within the time -- same for certification. Callback conversation with reporter revealed the following information: reporter said that no other controller for the remainder of their flight questioned altitude. The altitude encoder was sent to maintenance on arrival and found to meet specifications and recertified.

Original NASA ASRS Text

Title: ARTCC ALT READOUT DIFFERENT THAN BEING FLOWN. ACFT SYS CHKED AND FOUND CORRECT.

Narrative: WHILE CONTACTING ZBW FOR FLT FOLLOWING (WITH THE CORRECT ALTIMETER SETTING) WAS INFORMED BY THE CTLR THAT HIS EQUIP SHOWED US AT 300 FT HIGH. WE ACKNOWLEDGED HIS XMISSION. SPLIT THE DIFFERENCE BTWN READOUT AND ACTUAL ALT. NO OTHER CTLR HAD NOTED A PROB PRIOR TO THIS CTLR. IN THINKING ABOUT THIS LATER, I SHOULD HAVE STAYED AT THE CORRECT ALT. ON REACHING HOME ARPT, HAVE ASKED THE LCL REPAIR SHOP TO CHK THE ENCODER. HAVE NOT HAD A RPT BACK NOR HAVE WE USED THE ACFT. WE ALSO CHK THE LOGS, THE ENCODER WAS WITHIN THE TIME -- SAME FOR CERTIFICATION. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: RPTR SAID THAT NO OTHER CTLR FOR THE REMAINDER OF THEIR FLT QUESTIONED ALT. THE ALT ENCODER WAS SENT TO MAINT ON ARR AND FOUND TO MEET SPECS AND RECERTIFIED.

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.