Narrative:

This report concerns a problem that surfaced after landing at lax. The flight, all cargo. The entire flight was uneventful, except that the preflight was extensive due to lightning strikes on the previous leg. The only damage due to the lightning discovered in anc concerned a failure of the #2 HF, and eventually the aircraft was released for flight. After departure from anc center asked us to verify our altitude since this happened after level off it seemed a little odd but ATC did not elaborate on the request. On arrival into lax we were originally cleared for the 'profile descent' but were vectored off the arrival. We were cleared out of 13000 ft for 11000 ft and during that descent lax center asked us if we were at '10-8.' at that time we were passing 11100 and in the process of leveling off at 11000. We reported the 11100 ft reading and ATC made no comment. After the uneventful approach and landing, we were told to contact center, which we did. Lax center said they showed us at 8500 ft then climbing quickly back to 11000 ft and that this 'deviation' had caused them to vector departing traffic. We never descended to an 8500 ft altitude and never climbed from a lower to higher altitude during the arrival, maintenance removed the transponder and flight data recorder and replaced them before the aircraft was released. We assume an altitude readout problem possibly due to the lightning strikes.

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Original NASA ASRS Text

Title: ALTDEV ALT OVERSHOT SUSPECTED BY ARTCC RADAR CTLR DURING RADAR MONITORING OF AN ACR WDB FRT ACFT IN DSCNT PROC.

Narrative: THIS RPT CONCERNS A PROBLEM THAT SURFACED AFTER LNDG AT LAX. THE FLT, ALL CARGO. THE ENTIRE FLT WAS UNEVENTFUL, EXCEPT THAT THE PREFLT WAS EXTENSIVE DUE TO LIGHTNING STRIKES ON THE PREVIOUS LEG. THE ONLY DAMAGE DUE TO THE LIGHTNING DISCOVERED IN ANC CONCERNED A FAILURE OF THE #2 HF, AND EVENTUALLY THE ACFT WAS RELEASED FOR FLT. AFTER DEP FROM ANC CTR ASKED US TO VERIFY OUR ALT SINCE THIS HAPPENED AFTER LEVEL OFF IT SEEMED A LITTLE ODD BUT ATC DID NOT ELABORATE ON THE REQUEST. ON ARR INTO LAX WE WERE ORIGINALLY CLRED FOR THE 'PROFILE DSCNT' BUT WERE VECTORED OFF THE ARR. WE WERE CLRED OUT OF 13000 FT FOR 11000 FT AND DURING THAT DSCNT LAX CTR ASKED US IF WE WERE AT '10-8.' AT THAT TIME WE WERE PASSING 11100 AND IN THE PROCESS OF LEVELING OFF AT 11000. WE RPTED THE 11100 FT READING AND ATC MADE NO COMMENT. AFTER THE UNEVENTFUL APCH AND LNDG, WE WERE TOLD TO CONTACT CTR, WHICH WE DID. LAX CTR SAID THEY SHOWED US AT 8500 FT THEN CLBING QUICKLY BACK TO 11000 FT AND THAT THIS 'DEV' HAD CAUSED THEM TO VECTOR DEPARTING TFC. WE NEVER DSNDED TO AN 8500 FT ALT AND NEVER CLBED FROM A LOWER TO HIGHER ALT DURING THE ARR, MAINT REMOVED THE TRANSPONDER AND FLT DATA RECORDER AND REPLACED THEM BEFORE THE ACFT WAS RELEASED. WE ASSUME AN ALT READOUT PROBLEM POSSIBLY DUE TO THE LIGHTNING STRIKES.

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.