Narrative:

Flight from cle to phl. We were being vectored for approach. Last clearance from phl approach was to turn to 280 degrees with a descent to 4000 ft and intercept the localizer to runway 27R (it was a right turn for us coming in from the north). As we intercepted localizer, still descending to 4000 ft, approach advised us we had traffic at 9 O'clock, and to call the airport and the traffic when in sight. I, the captain, first officer flying, called the airport in sight, but did not have the 9 O'clock traffic. I continued to look for traffic. We then descended below 4000 ft. First officer believed we were cleared for the approach and was on runway 27R GS descending. I noticed deviation below 4000 ft at about 3800 ft, and with the recovery back up to 4000 ft. We descended to between 3750 ft and 3720 ft. At no time was the deviation greater than 280 ft, but it was enough to activate the altitude alerter. During our climb back to 4000 ft I asked phl approach if we were cleared for the approach, and he informed us we weren't. Before we leveled back to 4000 ft, approach cleared us for the ILS runway 27R. On the ground I called phl TRACON and talked to one of the people in the approach room. I told him what had happened and asked to speak with the controller who had worked our flight. He said he was busy and he said he didn't know of anything that had happened that would cause any concern.

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Original NASA ASRS Text

Title: THE FLC DSNDED THROUGH THEIR ASSIGNED 4000 FT TO 3750 FT BEFORE RETURNING TO 4000 FT AND CONFIRMING THEY IN FACT HAD NOT YET BEEN CLRED FOR THE APCH. THE CTLR INSTRUCTED THE FLC TO RPT AN AIRPLANE OR ARPT IN SIGHT FOR THE VISUAL APCH. THE PLTS COMPLIED, BUT IN FACT WERE NOT CLRED FOR THE VISUAL AFTER COMPLIANCE.

Narrative: FLT FROM CLE TO PHL. WE WERE BEING VECTORED FOR APCH. LAST CLRNC FROM PHL APCH WAS TO TURN TO 280 DEGS WITH A DSCNT TO 4000 FT AND INTERCEPT THE LOC TO RWY 27R (IT WAS A R TURN FOR US COMING IN FROM THE N). AS WE INTERCEPTED LOC, STILL DSNDING TO 4000 FT, APCH ADVISED US WE HAD TFC AT 9 O'CLOCK, AND TO CALL THE ARPT AND THE TFC WHEN IN SIGHT. I, THE CAPT, FO FLYING, CALLED THE ARPT IN SIGHT, BUT DID NOT HAVE THE 9 O'CLOCK TFC. I CONTINUED TO LOOK FOR TFC. WE THEN DSNDED BELOW 4000 FT. FO BELIEVED WE WERE CLRED FOR THE APCH AND WAS ON RWY 27R GS DSNDING. I NOTICED DEV BELOW 4000 FT AT ABOUT 3800 FT, AND WITH THE RECOVERY BACK UP TO 4000 FT. WE DSNDED TO BTWN 3750 FT AND 3720 FT. AT NO TIME WAS THE DEV GREATER THAN 280 FT, BUT IT WAS ENOUGH TO ACTIVATE THE ALT ALERTER. DURING OUR CLB BACK TO 4000 FT I ASKED PHL APCH IF WE WERE CLRED FOR THE APCH, AND HE INFORMED US WE WEREN'T. BEFORE WE LEVELED BACK TO 4000 FT, APCH CLRED US FOR THE ILS RWY 27R. ON THE GND I CALLED PHL TRACON AND TALKED TO ONE OF THE PEOPLE IN THE APCH ROOM. I TOLD HIM WHAT HAD HAPPENED AND ASKED TO SPEAK WITH THE CTLR WHO HAD WORKED OUR FLT. HE SAID HE WAS BUSY AND HE SAID HE DIDN'T KNOW OF ANYTHING THAT HAD HAPPENED THAT WOULD CAUSE ANY CONCERN.

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.