Narrative:

Aircraft altimeters had maintenance history of being out of tolerance. At FL370 captain's altimeter read 370, center altimeter 37725', first officer's 37350'. At same time ATC reported us to be at 36800'. We switched to alternate static source and ATC reported us at 36600' or 400' low and reported conflicting opposite direction traffic at FL350. We switched back to normal static source and climbed 200'.

Google
 

Original NASA ASRS Text

Title: ACR WDB ALT DEVIATION BECAUSE ACFT ALTIMETERS WERE OUT OF TOLERANCE.

Narrative: ACFT ALTIMETERS HAD MAINT HISTORY OF BEING OUT OF TOLERANCE. AT FL370 CAPT'S ALTIMETER READ 370, CENTER ALTIMETER 37725', F/O'S 37350'. AT SAME TIME ATC RPTED US TO BE AT 36800'. WE SWITCHED TO ALTERNATE STATIC SOURCE AND ATC RPTED US AT 36600' OR 400' LOW AND RPTED CONFLICTING OPPOSITE DIRECTION TFC AT FL350. WE SWITCHED BACK TO NORMAL STATIC SOURCE AND CLBED 200'.

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.