B747-200 captain reported the aircraft altitude in error in the position report to rpmm.

Attributes
ACN	541805
Time
Date	200203
Day	Thu
Local Time Of Day	1201 To 1800
Place
Locale Reference	intersection : bisig
State Reference	FO
Altitude	msl single value : 40000
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Operator	common carrier : air carrier
Make Model Name	B747-200
Operating Under FAR Part	Part 121
Navigation In Use	other
Flight Phase	cruise : enroute altitude change
Route In Use	enroute airway : a582.airway
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Experience	flight time last 90 days : 60 flight time total : 12000 flight time type : 8000
ASRS Report	541805
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Events
Anomaly	non adherence : far non adherence : company policies non adherence : published procedure other anomaly other
Independent Detector	aircraft equipment other aircraft equipment : altimeter other controllera
Resolutory Action	controller : issued advisory none taken : detected after the fact other
Supplementary
Problem Areas	Aircraft Flight Crew Human Performance
Primary Problem	Flight Crew Human Performance

Narrative:

En route sbound A-582. Prior to sakon, received clearance to climb and maintain FL390. Leveled at FL390, reported FL390 at sakon. Reclred to FL400 for direction of flight entering reduced vertical separation minimums airspace. Climbed to FL400. After leveloff, first officer's altimeter read 40010 ft. Captain's read 39965 ft. At bisig, and subsequently at elmas, captain prepared position reports for those fixes. Glancing up at his altimeter, he saw 39965 ft indicated and read it as FL390, which was also the same altitude as his preceding position report at sakon. FL390 then was written in on the flight plan and the position reports were read to manila radio as FL390. Several mins passed before manila radio called back to confirm the altitude. The captain then realized the error and clarified to ATC that the flight was indeed level FL400 and had been level at FL400 at bisig and elmas and that the FL390 report at those fixes had been in error. Factors contributing to the error were distraction due to meal service in the cockpit and the electronic altimeter display. Unlike most altimeters, the electronic altimeter does not employ a rotating drum in its digital readout. Consequently, the thousands display at 39990 ft looks identical to the thousands display at 39000 ft. Both electronic and rotating drum type altimeters are used within the fleet. I have encountered this type of 'read error' several times before this occurrence.

Original NASA ASRS Text

Title: B747-200 CAPT RPTED THE ACFT ALT IN ERROR IN THE POS RPT TO RPMM.

Narrative: ENRTE SBOUND A-582. PRIOR TO SAKON, RECEIVED CLRNC TO CLB AND MAINTAIN FL390. LEVELED AT FL390, RPTED FL390 AT SAKON. RECLRED TO FL400 FOR DIRECTION OF FLT ENTERING REDUCED VERT SEPARATION MINIMUMS AIRSPACE. CLBED TO FL400. AFTER LEVELOFF, FO'S ALTIMETER READ 40010 FT. CAPT'S READ 39965 FT. AT BISIG, AND SUBSEQUENTLY AT ELMAS, CAPT PREPARED POS RPTS FOR THOSE FIXES. GLANCING UP AT HIS ALTIMETER, HE SAW 39965 FT INDICATED AND READ IT AS FL390, WHICH WAS ALSO THE SAME ALT AS HIS PRECEDING POS RPT AT SAKON. FL390 THEN WAS WRITTEN IN ON THE FLT PLAN AND THE POS RPTS WERE READ TO MANILA RADIO AS FL390. SEVERAL MINS PASSED BEFORE MANILA RADIO CALLED BACK TO CONFIRM THE ALT. THE CAPT THEN REALIZED THE ERROR AND CLARIFIED TO ATC THAT THE FLT WAS INDEED LEVEL FL400 AND HAD BEEN LEVEL AT FL400 AT BISIG AND ELMAS AND THAT THE FL390 RPT AT THOSE FIXES HAD BEEN IN ERROR. FACTORS CONTRIBUTING TO THE ERROR WERE DISTR DUE TO MEAL SVC IN THE COCKPIT AND THE ELECTRONIC ALTIMETER DISPLAY. UNLIKE MOST ALTIMETERS, THE ELECTRONIC ALTIMETER DOES NOT EMPLOY A ROTATING DRUM IN ITS DIGITAL READOUT. CONSEQUENTLY, THE THOUSANDS DISPLAY AT 39990 FT LOOKS IDENTICAL TO THE THOUSANDS DISPLAY AT 39000 FT. BOTH ELECTRONIC AND ROTATING DRUM TYPE ALTIMETERS ARE USED WITHIN THE FLEET. I HAVE ENCOUNTERED THIS TYPE OF 'READ ERROR' SEVERAL TIMES BEFORE THIS OCCURRENCE.

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.