Narrative:

Captain, PF, first officer, PNF, observed FMA switch from IAS to altitude capture. We were then given a 30 degree heading change executed at 25 degree bank. I looked down at approach chart for ILS frequency and heard altitude warning. Altitude was now 6700 ft. Autoplt did not execute altitude hold. Autoplt was disconnected and aircraft flown back to 7000 ft. No conflict with other aircraft observed or mentioned by us or ATC. Supplemental information from acn 395700: on autoplt the captain selected heading and the aircraft rolled into 30 degrees of bank as altitude capture was annunciated on the FMA. As copilot PNF my job is to back up the PF, but in this case to back up actual altitude I have to go xcockpit due to afl altitudes on the first officer's altimeter.

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Original NASA ASRS Text

Title: MD80S ACFT BEING VECTORED FOR APCH WITH ACFT MANEUVERING, RPTR CAPT THOUGHT THE AUTOPLT HAD CAPTURED AND WOULD HOLD ALT, BUT IT DIDN'T AND ACFT LOST 300 FT WHILE IN TURN.

Narrative: CAPT, PF, FO, PNF, OBSERVED FMA SWITCH FROM IAS TO ALT CAPTURE. WE WERE THEN GIVEN A 30 DEG HDG CHANGE EXECUTED AT 25 DEG BANK. I LOOKED DOWN AT APCH CHART FOR ILS FREQ AND HEARD ALT WARNING. ALT WAS NOW 6700 FT. AUTOPLT DID NOT EXECUTE ALT HOLD. AUTOPLT WAS DISCONNECTED AND ACFT FLOWN BACK TO 7000 FT. NO CONFLICT WITH OTHER ACFT OBSERVED OR MENTIONED BY US OR ATC. SUPPLEMENTAL INFO FROM ACN 395700: ON AUTOPLT THE CAPT SELECTED HEADING AND THE ACFT ROLLED INTO 30 DEGS OF BANK AS ALT CAPTURE WAS ANNUNCIATED ON THE FMA. AS COPLT PNF MY JOB IS TO BACK UP THE PF, BUT IN THIS CASE TO BACK UP ACTUAL ALT I HAVE TO GO XCOCKPIT DUE TO AFL ALTS ON THE FO'S ALTIMETER.

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.