Similar sounding call signs leads to 2 different aircraft accepting each other's clearance.

Attributes
ACN	519670
Time
Date	200107
Day	Wed
Local Time Of Day	1201 To 1800
Place
Locale Reference	airport : phl.airport
State Reference	PA
Altitude	msl bound lower : 13000 msl bound upper : 13500
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Operator	common carrier : air carrier
Make Model Name	Large Transport, Low Wing, 2 Turbojet Eng
Flight Phase	climbout : intermediate altitude
Flight Plan	IFR
Aircraft 2
Controlling Facilities	artcc : zny.artcc
Operator	common carrier : air carrier
Make Model Name	Commercial Fixed Wing
Flight Phase	climbout : intermediate altitude
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : instrument pilot : cfi pilot : atp pilot : multi engine pilot : commercial
Experience	flight time last 90 days : 145 flight time total : 7100 flight time type : 650
ASRS Report	519670
Events
Anomaly	altitude deviation : overshoot non adherence : clearance other anomaly other
Resolutory Action	controller : issued new clearance controller : issued advisory flight crew : returned to assigned altitude
Consequence	faa : reviewed incident with flight crew
Supplementary
Problem Areas	Flight Crew Human Performance ATC Human Performance
Primary Problem	ATC Human Performance

Narrative:

Flight ab departed phl at XA23. Around XA45 we were cleared to climb to 13000 ft. Climbing through 11500 ft, we were cleared to FL260. We read back the clearance to FL260. There was also a similar call sign who joined us on the same frequency. Climbing through 12500 ft, we called ZNY to confirm again that we were leaving 12500 ft to FL260. At 13500 ft, the controller asked us to maintain 13000 ft and 10 seconds later he cleared us to climb to FL230. In the meantime, the ZNY controller also asked aircraft Y for its altitude. With almost similar call signs on a congested frequency, we wanted to confirm our assigned altitude. The controllers and the pilots have to be careful and read back all clrncs. Any time in doubt, ask again, especially when there are 2 airplanes with almost similar call signs on a busy frequency.

Original NASA ASRS Text

Title: SIMILAR SOUNDING CALL SIGNS LEADS TO 2 DIFFERENT ACFT ACCEPTING EACH OTHER'S CLRNC.

Narrative: FLT AB DEPARTED PHL AT XA23. AROUND XA45 WE WERE CLRED TO CLB TO 13000 FT. CLBING THROUGH 11500 FT, WE WERE CLRED TO FL260. WE READ BACK THE CLRNC TO FL260. THERE WAS ALSO A SIMILAR CALL SIGN WHO JOINED US ON THE SAME FREQ. CLBING THROUGH 12500 FT, WE CALLED ZNY TO CONFIRM AGAIN THAT WE WERE LEAVING 12500 FT TO FL260. AT 13500 FT, THE CTLR ASKED US TO MAINTAIN 13000 FT AND 10 SECONDS LATER HE CLRED US TO CLB TO FL230. IN THE MEANTIME, THE ZNY CTLR ALSO ASKED ACFT Y FOR ITS ALT. WITH ALMOST SIMILAR CALL SIGNS ON A CONGESTED FREQ, WE WANTED TO CONFIRM OUR ASSIGNED ALT. THE CTLRS AND THE PLTS HAVE TO BE CAREFUL AND READ BACK ALL CLRNCS. ANY TIME IN DOUBT, ASK AGAIN, ESPECIALLY WHEN THERE ARE 2 AIRPLANES WITH ALMOST SIMILAR CALL SIGNS ON A BUSY FREQ.

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.