AN A320 CREW DURING DSCNT OVERSHOT ASSIGNED ALT.

Narrative

I WAS THE CAPT OF THIS FLT AND ALSO THE PNF. THE FLT WAS UNEVENTFUL UNTIL THE DSCNT INTO PHL. AS WE APCHED SIE FROM CHAMP INTXN; WE WERE CLRED TO CROSS 35 MI SE OF SIE AT 16000 FT. DURING THE DSCNT; IT BECAME NECESSARY TO USE THE SPD BRAKE IN ORDER TO MAKE THE XING RESTR. A DISCUSSION BEGAN REGARDING THE FACT THAT YOU CAN ONLY GET ABOUT 1/2 OF THE SPD BRAKE WITH THE AUTOPLT ON. THE FO AND PF THEN DISCONNECTED THE AUTOPLT; AND WAS ABLE TO SEE THE INCREASED SPD BRAKE DEFLECTION AND DSCNT RATE. AS WE APCHED 17500 FT; I CALLED OUT '17000 FT FOR 16000 FT' DUE TO THE HIGH DSCNT RATE. THE FO CALLED OUT '17000 FT FOR 16000 FT' AS WE PASSED 17000 FT. WITH A HIGH DSCNT RATE STILL EVIDENT AT 16500 FT; I TOLD THE FO TO LEVEL AT 16000 FT; AND HE REPLIED THAT HE WOULD. THE ACFT DSNDED BELOW 16000 FT AND AT 15750 FT; THE ALT ALERTER SOUNDED. I THEN USED MY SIDE STICK CTL TO CORRECT FOR THE ALTDEV. THE ACFT PITCHED UP MORE ABRUPTLY THAN I WOULD HAVE PREFERRED; AND THEN THE 'DUAL INPUT' AURAL ANNUNCIATION SOUNDED. I THEN RELAXED MY CTL INPUT AS IT WAS NOW OBVIOUS THAT THE FO WAS CORRECTING FOR THE DEV. THE FO EXPLAINED THAT HE FORGOT HE HAD DISCONNECTED THE AUTOPLT. HE SAW 'ALT' DISPLAYED ON THE FMA; AND ASSUMED THE AUTOPLT WOULD LEVEL THE ACFT AT 16000 FT. HE OBVIOUSLY OVERLOOKED THE FACT THE FMA DID NOT SHOW THE AUTOPLT WAS ON. TO MY BEST RECOLLECTION; THE LOWEST ALT THAT I OBSERVED WAS 15600 FT. NO CONFLICTING TFC WAS DISPLAYED ON THE TCASII; AND THE CTLR MADE NO COMMENT ON THE DEV.