Narrative:

After takeoff we had several EICAS messages relating to a difference in airspeed indications. We analyzed the problems and communicated with dispatch and maintenance control to see how to resolve them. It was determined that we had already done everything we could by selecting the alternate air data computer on the captain's side. The autoplt was working; but after awhile at cruise it tripped off and would not reset due to an 'elev asymm' status message. Initially I thought of telling ATC; but first communicated with dispatch about communicating again with maintenance control on diverting or continuing on to destination depending on if they could fix the aircraft at destination. The first officer and I had already discussed whether to continue by hand-flying or divert. We determined that we were well rested and could hand-fly by swapping out every half hour. I did not advise ATC of the autoplt failure as we had everything under control. In reviewing what we did it was my only mistake due to being in rvsm airspace; and should have advised them due to the autoplt failure. While we were able to maintain our altitude fairly easily and did not have any conflicts due to the time of day; the good WX; and airspace we were flying in. Had we been challenged by rough air; WX; or another problem; maintaining altitude could have been a problem.

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Original NASA ASRS Text

Title: A B757-200 CREW WITH AN AIRSPEED MALFUNCTION CONTINUED IN RVSM FLT WHEN A DESCENT OUT OF RVSM WAS REQUIRED.

Narrative: AFTER TKOF WE HAD SEVERAL EICAS MESSAGES RELATING TO A DIFFERENCE IN AIRSPD INDICATIONS. WE ANALYZED THE PROBS AND COMMUNICATED WITH DISPATCH AND MAINT CTL TO SEE HOW TO RESOLVE THEM. IT WAS DETERMINED THAT WE HAD ALREADY DONE EVERYTHING WE COULD BY SELECTING THE ALTERNATE ADC ON THE CAPT'S SIDE. THE AUTOPLT WAS WORKING; BUT AFTER AWHILE AT CRUISE IT TRIPPED OFF AND WOULD NOT RESET DUE TO AN 'ELEV ASYMM' STATUS MESSAGE. INITIALLY I THOUGHT OF TELLING ATC; BUT FIRST COMMUNICATED WITH DISPATCH ABOUT COMMUNICATING AGAIN WITH MAINT CTL ON DIVERTING OR CONTINUING ON TO DEST DEPENDING ON IF THEY COULD FIX THE ACFT AT DEST. THE FO AND I HAD ALREADY DISCUSSED WHETHER TO CONTINUE BY HAND-FLYING OR DIVERT. WE DETERMINED THAT WE WERE WELL RESTED AND COULD HAND-FLY BY SWAPPING OUT EVERY HALF HR. I DID NOT ADVISE ATC OF THE AUTOPLT FAILURE AS WE HAD EVERYTHING UNDER CTL. IN REVIEWING WHAT WE DID IT WAS MY ONLY MISTAKE DUE TO BEING IN RVSM AIRSPACE; AND SHOULD HAVE ADVISED THEM DUE TO THE AUTOPLT FAILURE. WHILE WE WERE ABLE TO MAINTAIN OUR ALT FAIRLY EASILY AND DID NOT HAVE ANY CONFLICTS DUE TO THE TIME OF DAY; THE GOOD WX; AND AIRSPACE WE WERE FLYING IN. HAD WE BEEN CHALLENGED BY ROUGH AIR; WX; OR ANOTHER PROB; MAINTAINING ALT COULD HAVE BEEN A PROB.

Data retrieved from NASA's ASRS site as of January 2009 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.