Phraseology: easy to misunderstand. Like mentioned earlier: why not use "departing" or "taking off"? Here in my neck of the woods they sometimes use "...behind traffic
on the roll off runway XY". I think I would have probably interpreted "rolling off" as (a just landed) aircraft exiting the runway (although it would raise a question why the 737 was facing towards the end of the runway - respectively the hold short line - when it supposedly just exited the runway?).
FH1100: I respectfully disagree (of course not on the "not paying attention"-part
):
If the 737 was taxiing towards the runway for departure, he was facing the opposite heading than the runway, so he would have passed "behind" that traffic by crossing over the departure end. HOWEVER looking at the airport layout its hard to imagine what the helicopter pilot intended to do - land on the ramp or cross midfield? If he intended to land or was just following the M1 motor-way, he was pretty much "behind"
every aircraft on that airport
.
Also the TCAS issue: I stand corrected, but even if the Lear's transponder was switched to On or Alt, I assume most transponders are interrupted by a squat switch in the landing gear anyway?