Narrative:

We called ilg ground for a taxi clearance for westwind nxxxx for a VFR flight northwest to lns airport. We were told to taxi to runway 1 and hold short of runway 32. As we approached runway 32 we were given further taxi instructions to taxi to the approach end of runway 1 for full length departure and switch over to tower frequency. As we approached runway 1 I gave control of the aircraft to the first officer and pushed the switch for tower frequency. I thought the tower said 'nxyy cleared for takeoff left turnout.' as the aircraft lined up on the runway and the takeoff checks were complete, I saw a cessna single rotate just west of runway 1 on runway 9. I thought this was unusual and kept my attention on that traffic. As we rotated and retracted the gear, we passed behind that cessna traffic. Then tower called to ask us 'who cleared you for takeoff?' I replied, 'you did.' they said they did not. A later call to tower revealed that when I changed over to tower frequency I heard the tower clear the cessna to go with left traffic and that the other aircraft had a similar call sign 'xy' as opposed to 'yx.' I feel that had we been issued a definite 'hold short of runway 1' clearance this event might not have happened. It also points out the need to pay close attention to radio instructions and ask for confirmation if there is any doubt.

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Original NASA ASRS Text

Title: FLC OF AN ISRAEL IA 1123 WESTWIND, TOOK OFF IN RESPONSE TO AN SEL CESSNA SIMILAR SOUNDING CALL SIGN.

Narrative: WE CALLED ILG GND FOR A TAXI CLRNC FOR WESTWIND NXXXX FOR A VFR FLT NW TO LNS ARPT. WE WERE TOLD TO TAXI TO RWY 1 AND HOLD SHORT OF RWY 32. AS WE APCHED RWY 32 WE WERE GIVEN FURTHER TAXI INSTRUCTIONS TO TAXI TO THE APCH END OF RWY 1 FOR FULL LENGTH DEP AND SWITCH OVER TO TWR FREQ. AS WE APCHED RWY 1 I GAVE CTL OF THE ACFT TO THE FO AND PUSHED THE SWITCH FOR TWR FREQ. I THOUGHT THE TWR SAID 'NXYY CLRED FOR TKOF L TURNOUT.' AS THE ACFT LINED UP ON THE RWY AND THE TKOF CHKS WERE COMPLETE, I SAW A CESSNA SINGLE ROTATE JUST W OF RWY 1 ON RWY 9. I THOUGHT THIS WAS UNUSUAL AND KEPT MY ATTN ON THAT TFC. AS WE ROTATED AND RETRACTED THE GEAR, WE PASSED BEHIND THAT CESSNA TFC. THEN TWR CALLED TO ASK US 'WHO CLRED YOU FOR TKOF?' I REPLIED, 'YOU DID.' THEY SAID THEY DID NOT. A LATER CALL TO TWR REVEALED THAT WHEN I CHANGED OVER TO TWR FREQ I HEARD THE TWR CLR THE CESSNA TO GO WITH L TFC AND THAT THE OTHER ACFT HAD A SIMILAR CALL SIGN 'XY' AS OPPOSED TO 'YX.' I FEEL THAT HAD WE BEEN ISSUED A DEFINITE 'HOLD SHORT OF RWY 1' CLRNC THIS EVENT MIGHT NOT HAVE HAPPENED. IT ALSO POINTS OUT THE NEED TO PAY CLOSE ATTN TO RADIO INSTRUCTIONS AND ASK FOR CONFIRMATION IF THERE IS ANY DOUBT.

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.