Narrative:

Departed phl airport runway 27L at approximately XP40 hours flying the phl 6 SID with clearance to 5000 ft. The autoplt was off. Upon initial contact with phl departure, the controller vectored our aircraft (X) to the south and cleared us to 10000 ft. The PNF acknowledged/read back ATC clearance to 10000 ft. Both pilots followed company altitude awareness procedures as outlined in the company flight operations manual, ie, PNF sets, points to, and verbally states the newly assigned altitude. PF verbally states the ATC assigned altitude and points to the selected altitude to confirm agreement. A jump seat pilot witnessed these actions. As the aircraft was passing through 9700 ft, the controller stated our assigned altitude was 9000 ft and instructed us to descend to that altitude. PNF advised that our last assigned altitude was 10000 ft, but that we were descending to 9000 ft. Crew reported level at 9000 ft and at no time did TCASII show a TA or RA. Shortly after turning us to the east, the controller reported traffic as a 'T2' (Y) and that we could expect higher when clear of traffic. The controller made no comment regarding any separation problem. We were eventually cleared back to 10000 ft and handed off to ZNY. This problem may have been caused by allowing an aircraft to transit a busy airline departure corridor during a peak traffic period. Phl departure routinely clears aircraft to 10000 ft when departing to the west (runway 27). This controller cleared us to 10000 ft (perhaps out of habit) and then realized a transiting aircraft might create a conflict.

Related reports:

Google
 

Original NASA ASRS Text

Title: PHL CTLR CHALLENGED A319 FLC ON OVERSHOOT CLB WITH POTENTIAL CONFLICTING T2, THOUGH NOT IN IMMEDIATE VICINITY.

Narrative: DEPARTED PHL ARPT RWY 27L AT APPROX XP40 HRS FLYING THE PHL 6 SID WITH CLRNC TO 5000 FT. THE AUTOPLT WAS OFF. UPON INITIAL CONTACT WITH PHL DEP, THE CTLR VECTORED OUR ACFT (X) TO THE S AND CLRED US TO 10000 FT. THE PNF ACKNOWLEDGED/READ BACK ATC CLRNC TO 10000 FT. BOTH PLTS FOLLOWED COMPANY ALT AWARENESS PROCS AS OUTLINED IN THE COMPANY FLT OPS MANUAL, IE, PNF SETS, POINTS TO, AND VERBALLY STATES THE NEWLY ASSIGNED ALT. PF VERBALLY STATES THE ATC ASSIGNED ALT AND POINTS TO THE SELECTED ALT TO CONFIRM AGREEMENT. A JUMP SEAT PLT WITNESSED THESE ACTIONS. AS THE ACFT WAS PASSING THROUGH 9700 FT, THE CTLR STATED OUR ASSIGNED ALT WAS 9000 FT AND INSTRUCTED US TO DSND TO THAT ALT. PNF ADVISED THAT OUR LAST ASSIGNED ALT WAS 10000 FT, BUT THAT WE WERE DSNDING TO 9000 FT. CREW RPTED LEVEL AT 9000 FT AND AT NO TIME DID TCASII SHOW A TA OR RA. SHORTLY AFTER TURNING US TO THE E, THE CTLR RPTED TFC AS A 'T2' (Y) AND THAT WE COULD EXPECT HIGHER WHEN CLR OF TFC. THE CTLR MADE NO COMMENT REGARDING ANY SEPARATION PROB. WE WERE EVENTUALLY CLRED BACK TO 10000 FT AND HANDED OFF TO ZNY. THIS PROB MAY HAVE BEEN CAUSED BY ALLOWING AN ACFT TO TRANSIT A BUSY AIRLINE DEP CORRIDOR DURING A PEAK TFC PERIOD. PHL DEP ROUTINELY CLRS ACFT TO 10000 FT WHEN DEPARTING TO THE W (RWY 27). THIS CTLR CLRED US TO 10000 FT (PERHAPS OUT OF HABIT) AND THEN REALIZED A TRANSITING ACFT MIGHT CREATE A CONFLICT.

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.