Narrative:

I was the captain of this flight and also the PNF. The flight was uneventful until the descent into phl. As we approached sie from champ intersection, we were cleared to cross 35 mi southeast of sie at 16000 ft. During the descent, it became necessary to use the speed brake in order to make the crossing restr. A discussion began regarding the fact that you can only get about 1/2 of the speed brake with the autoplt on. The first officer and PF then disconnected the autoplt, and was able to see the increased speed brake deflection and descent rate. As we approached 17500 ft, I called out '17000 ft for 16000 ft' due to the high descent rate. The first officer called out '17000 ft for 16000 ft' as we passed 17000 ft. With a high descent rate still evident at 16500 ft, I told the first officer to level at 16000 ft, and he replied that he would. The aircraft descended below 16000 ft and at 15750 ft, the altitude alerter sounded. I then used my side stick control to correct for the altitude deviation. The aircraft pitched up more abruptly than I would have preferred, and then the 'dual input' aural annunciation sounded. I then relaxed my control input as it was now obvious that the first officer was correcting for the deviation. The first officer explained that he forgot he had disconnected the autoplt. He saw 'altitude' displayed on the FMA, and assumed the autoplt would level the aircraft at 16000 ft. He obviously overlooked the fact the FMA did not show the autoplt was on. To my best recollection, the lowest altitude that I observed was 15600 ft. No conflicting traffic was displayed on the TCASII, and the controller made no comment on the deviation.

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Original NASA ASRS Text

Title: 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.

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.