Cargo aircraft in a night operation advised that altitude encoder showed him to be 300 ft high at FL...

Attributes
ACN	359117
Time
Date	199701
Day	Tue
Local Time Of Day	0001 To 0600
Place
Locale Reference	atc facility : iln
State Reference	OH
Altitude	msl bound lower : 24000 msl bound upper : 24300
Environment
Flight Conditions	VMC
Light	Night
Aircraft 1
Controlling Facilities	artcc : zob tower : hrl
Operator	common carrier : air carrier
Make Model Name	Commercial Fixed Wing
Operating Under FAR Part	Part 121
Navigation In Use	Other
Flight Phase	climbout : intermediate altitude cruise other
Route In Use	enroute other
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Experience	flight time last 90 days : 200 flight time total : 14000 flight time type : 6000
ASRS Report	359117
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : commercial pilot : instrument
Events
Anomaly	aircraft equipment problem : less severe non adherence : far other anomaly other
Independent Detector	other controllera
Resolutory Action	none taken : unable
Consequence	Other
Supplementary
Primary Problem	Aircraft
Air Traffic Incident	other

Narrative:

During climb out from iln and after intermediate leveloff at FL240, ATC reported altitude as high, FL243. First officer's altimeter indicated FL242, altimeter 29.92 set. Captain's indicated FL240, altimeter set at 29.92, #2 transponder was in use. Swapped to #1 transponder and controller reported reading was still 300 ft high. We checked altitude several times during climb to FL310. Next controller verified level FL310. At end of flight, wrote up #1 and #2 transponder encoder for maintenance check. Form submitted because possible traffic conflict.

Original NASA ASRS Text

Title: CARGO ACFT IN A NIGHT OP ADVISED THAT ALT ENCODER SHOWED HIM TO BE 300 FT HIGH AT FL240.

Narrative: DURING CLBOUT FROM ILN AND AFTER INTERMEDIATE LEVELOFF AT FL240, ATC RPTED ALT AS HIGH, FL243. FO'S ALTIMETER INDICATED FL242, ALTIMETER 29.92 SET. CAPT'S INDICATED FL240, ALTIMETER SET AT 29.92, #2 XPONDER WAS IN USE. SWAPPED TO #1 XPONDER AND CTLR RPTED READING WAS STILL 300 FT HIGH. WE CHKED ALT SEVERAL TIMES DURING CLB TO FL310. NEXT CTLR VERIFIED LEVEL FL310. AT END OF FLT, WROTE UP #1 AND #2 XPONDER ENCODER FOR MAINT CHK. FORM SUBMITTED BECAUSE POSSIBLE TFC CONFLICT.

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.

Cargo aircraft in a night operation advised that altitude encoder showed him to be 300 ft high at FL240.