Narrative:

I was working the south departure/dupont sector at phl approach control. I released the HS25 from ilg. When I was contacted by the aircraft I radar idented it, issued a vector on course, and climbed the aft to 10000 ft. My exact phraseology was 'climb and maintain one-zero, ten thousand.' the pilot read back 'one-two thousand.' I did not catch the readback error. A few moments later, I observed the aircraft climbing through 11000 ft. I stated to the pilot that I had assigned an altitude of 10000 ft. I then issued an immediate descent clearance to 10000 ft and traffic to the HS25 that was 12 O'clock and 2 mi at 12000 ft. The pilot of the HS25 stated they had the traffic in sight and I issued instructions to maintain visual separation. I then effected coordination with ZNY and had control jurisdiction for the other aircraft. I feel increased pilot vigilance could have prevented this situation. I did not anticipate an incorrect readback, especially after I had reiterated the altitude.

Related reports:

Google
 

Original NASA ASRS Text

Title: PHL CTLR MISSES INCORRECT HS25 READBACK AND IT PENETRATES ZNY AIRSPACE AND CONFLICTS WITH ENRTE DHC8.

Narrative: I WAS WORKING THE S DEP/DUPONT SECTOR AT PHL APCH CTL. I RELEASED THE HS25 FROM ILG. WHEN I WAS CONTACTED BY THE ACFT I RADAR IDENTED IT, ISSUED A VECTOR ON COURSE, AND CLBED THE AFT TO 10000 FT. MY EXACT PHRASEOLOGY WAS 'CLB AND MAINTAIN ONE-ZERO, TEN THOUSAND.' THE PLT READ BACK 'ONE-TWO THOUSAND.' I DID NOT CATCH THE READBACK ERROR. A FEW MOMENTS LATER, I OBSERVED THE ACFT CLBING THROUGH 11000 FT. I STATED TO THE PLT THAT I HAD ASSIGNED AN ALT OF 10000 FT. I THEN ISSUED AN IMMEDIATE DSCNT CLRNC TO 10000 FT AND TFC TO THE HS25 THAT WAS 12 O'CLOCK AND 2 MI AT 12000 FT. THE PLT OF THE HS25 STATED THEY HAD THE TFC IN SIGHT AND I ISSUED INSTRUCTIONS TO MAINTAIN VISUAL SEPARATION. I THEN EFFECTED COORD WITH ZNY AND HAD CTL JURISDICTION FOR THE OTHER ACFT. I FEEL INCREASED PLT VIGILANCE COULD HAVE PREVENTED THIS SIT. I DID NOT ANTICIPATE AN INCORRECT READBACK, ESPECIALLY AFTER I HAD REITERATED THE ALT.

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.