A B727's autopilot failed to maintain engaged altitude.
Synopsis
A B727's autopilot failed to maintain engaged altitude.
Narrative
Rewritten in plain English from NASA’s original all-caps telegraphic report — facts, figures, and terminology preserved.
Tampa to Atlanta. Flight level 350, autopilot in use, straight and level. Autopilot malfunction.
Aircraft climbed very slowly from flight level 350 to flight level 355 (500 feet high). No aural warning and no indication in cockpit that autopilot malfunctioned except for altimeter. ATC did not remark on this situation.
We went back down to flight level 350; put autopilot back on. Autopilot deviated again. We wrote it up and hand flew to Atlanta.
Show the original NASA report (verbatim, telegraphic)
TAMPA TO ATLANTA. FL350 AUTOPLT IN USE STRAIGHT AND LEVEL. AUTOPLT MALFUNCTION. ACFT CLBED VERY SLOWLY FROM FL350 TO FL355 (500 FT HIGH). NO AURAL WARNING AND NO INDICATION IN COCKPIT THAT AUTOPLT MALFUNCTIONED EXCEPT FOR ALTIMETER. ATC DID NOT REMARK ON THIS SIT. WE WENT BACK DOWN TO FL350; PUT AUTOPLT BACK ON. AUTOPLT DEVIATED AGAIN. WE WROTE IT UP AND HAND FLEW TO ATLANTA.
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Source: NASA Aviation Safety Reporting System (public domain). Reports are voluntary submissions and are not verified by NASA.