Narrative:

Departing rsw at night after runup, I contacted the tower and was given the following clearance: 'taxi into position and hold. Traffic is a helicopter crossing the west end from the south.' I mistakenly heard: 'cleared for immediate. Traffic is a helicopter crossing....' I scanned for and located the traffic and replied 'got the traffic, rolling.' just after rotating and lifting off, the controller cleared me for takeoff and assigned a heading (runway). At this point the helicopter had just crossed the far end of the runway. I mumbled an apology to the controller and read back his clearance including the heading. Since the runway is 12000 ft long and I had chosen to use the whole thing for takeoff, I was still about 1 mi from the helicopter when it crossed the runway. I have an onboard clearance recorder so I played back the first takeoff clearance and my reply. The controller clearly said 'position and hold' so I can only guess that my mind heard 'takeoff' only because that's what I expected. I do believe that the mention of the 'traffic crossing' created a distraction which contributed to my mental lapse. I suspect that the controller never realized my mistake or else he determined that it didn't result in a dangerous situation as there was no mention of my transgression on the air. The field was very quiet at the time. Other factors: this was the first time I was at rsw. I may have felt 'rushed' trying to keep out of the way of the airliner traffic. When I landed earlier the same day I was asked to taxi 'smartly' to speed things up and I complied happily (and was thanked). Also the trip was to an airport only 20 mins away and I have noticed that I tend to use less caution on short trips, probably due to a subconscious thought that nothing bad could happen on such a short trip. I was the sole occupant of the aircraft.

Google
 

Original NASA ASRS Text

Title: A BE55 PLT MISHEARD ATC INSTRUCTION AND DEPARTED RSW WITHOUT CLRNC.

Narrative: DEPARTING RSW AT NIGHT AFTER RUNUP, I CONTACTED THE TWR AND WAS GIVEN THE FOLLOWING CLRNC: 'TAXI INTO POS AND HOLD. TFC IS A HELI XING THE W END FROM THE S.' I MISTAKENLY HEARD: 'CLRED FOR IMMEDIATE. TFC IS A HELI XING....' I SCANNED FOR AND LOCATED THE TFC AND REPLIED 'GOT THE TFC, ROLLING.' JUST AFTER ROTATING AND LIFTING OFF, THE CTLR CLRED ME FOR TKOF AND ASSIGNED A HDG (RWY). AT THIS POINT THE HELI HAD JUST CROSSED THE FAR END OF THE RWY. I MUMBLED AN APOLOGY TO THE CTLR AND READ BACK HIS CLRNC INCLUDING THE HDG. SINCE THE RWY IS 12000 FT LONG AND I HAD CHOSEN TO USE THE WHOLE THING FOR TKOF, I WAS STILL ABOUT 1 MI FROM THE HELI WHEN IT CROSSED THE RWY. I HAVE AN ONBOARD CLRNC RECORDER SO I PLAYED BACK THE FIRST TKOF CLRNC AND MY REPLY. THE CTLR CLRLY SAID 'POS AND HOLD' SO I CAN ONLY GUESS THAT MY MIND HEARD 'TKOF' ONLY BECAUSE THAT'S WHAT I EXPECTED. I DO BELIEVE THAT THE MENTION OF THE 'TFC XING' CREATED A DISTR WHICH CONTRIBUTED TO MY MENTAL LAPSE. I SUSPECT THAT THE CTLR NEVER REALIZED MY MISTAKE OR ELSE HE DETERMINED THAT IT DIDN'T RESULT IN A DANGEROUS SIT AS THERE WAS NO MENTION OF MY TRANSGRESSION ON THE AIR. THE FIELD WAS VERY QUIET AT THE TIME. OTHER FACTORS: THIS WAS THE FIRST TIME I WAS AT RSW. I MAY HAVE FELT 'RUSHED' TRYING TO KEEP OUT OF THE WAY OF THE AIRLINER TFC. WHEN I LANDED EARLIER THE SAME DAY I WAS ASKED TO TAXI 'SMARTLY' TO SPD THINGS UP AND I COMPLIED HAPPILY (AND WAS THANKED). ALSO THE TRIP WAS TO AN ARPT ONLY 20 MINS AWAY AND I HAVE NOTICED THAT I TEND TO USE LESS CAUTION ON SHORT TRIPS, PROBABLY DUE TO A SUBCONSCIOUS THOUGHT THAT NOTHING BAD COULD HAPPEN ON SUCH A SHORT TRIP. I WAS THE SOLE OCCUPANT OF THE ACFT.

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.