Narrative:

Tower cleared me to 'line up and wait; traffic crossing runway; caution wake turbulence' at which time I requested a 2-minute delay for wake turbulence. The controller repeated the lineup and wait clearance; and added delay at your discretion. I waited 2minutes; and then began my take off roll at the end of two-minute period. At about 2000 feet into take off roll; I noticed an airliner exiting the left side of the runway toward the end of the runway. I reduced power for 2 seconds; about the time I reduced power the plane had exited the runway and I reapplied power and lifted off. Upon reaching 200 feet AGL; the tower called and told me I had not been cleared for takeoff. I continued on to my destination of after the tower requested I call a number after I reached my destination.I must have been concentrating so much about the wake turbulence of the 737 that had taken off in front of me that I took the phrase 'delay at your discretion' as a takeoff clearance when in fact one had not been issued. Other contributing factors: I had just completed a two-day refresher course in the baron simulator; which had been very rigorous and I must have been more fatigued than I realized. That; combined with anxiety over wake turbulence from the busy airline traffic; caused me not to concentrate on the clearance given interpreting the phrase 'at my discretion' as a release clearance for takeoff. It might be better phraseology to say; 'line up and wait for takeoff clearance' to reinforce in the pilots mind the exact instruction given. Fixation on wake turbulence seems to have caused the lack of attention to the actual instruction. It wasn't until the controller reminded me I had not been cleared for takeoff that the fact registered with me that I had for whatever reason taken off without being cleared to do so. I had focused on the time to hold for wake turbulence over the actual clearance.light aircraft holding in position on the runway with airliners waiting is not a comfortable position. It might be safer for the controller to hold the lighter aircraft on the taxiway until they can issue a takeoff clearance instead of a line up and wait. This would alleviate the potential of inadvertent takeoffs. Definitely a brain lapse. For older pilots the new wording versus the old 'hold in position' may have some psychological disconnect versus the more ingrained terminology used for many years.

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Original NASA ASRS Text

Title: BE-55 pilot reported taking off without clearance after misunderstanding Tower phraseology.

Narrative: Tower cleared me to 'line up and wait; traffic crossing runway; caution wake turbulence' at which time I requested a 2-minute delay for wake turbulence. The Controller repeated the lineup and wait clearance; and added delay at your discretion. I waited 2minutes; and then began my take off roll at the end of two-minute period. At about 2000 feet into take off roll; I noticed an airliner exiting the left side of the runway toward the end of the runway. I reduced power for 2 seconds; about the time I reduced power the plane had exited the runway and I reapplied power and lifted off. Upon reaching 200 feet AGL; the Tower called and told me I had not been cleared for takeoff. I continued on to my destination of after the Tower requested I call a number after I reached my destination.I must have been concentrating so much about the wake turbulence of the 737 that had taken off in front of me that I took the phrase 'delay at your discretion' as a takeoff clearance when in fact one had not been issued. Other contributing factors: I had just completed a two-day refresher course in the Baron simulator; which had been very rigorous and I must have been more fatigued than I realized. That; combined with anxiety over wake turbulence from the busy airline traffic; caused me not to concentrate on the clearance given interpreting the phrase 'at my discretion' as a release clearance for takeoff. It might be better phraseology to say; 'Line up and wait for takeoff clearance' to reinforce in the pilots mind the exact instruction given. Fixation on wake turbulence seems to have caused the lack of attention to the actual instruction. It wasn't until the Controller reminded me I had not been cleared for takeoff that the fact registered with me that I had for whatever reason taken off without being cleared to do so. I had focused on the time to hold for wake turbulence over the actual clearance.Light aircraft holding in position on the runway with airliners waiting is not a comfortable position. It might be safer for the Controller to hold the lighter aircraft on the taxiway until they can issue a takeoff clearance instead of a line up and wait. This would alleviate the potential of inadvertent takeoffs. Definitely a brain lapse. For older pilots the new wording versus the old 'Hold in Position' may have some psychological disconnect versus the more ingrained terminology used for many years.

Data retrieved from NASA's ASRS site 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.