Separation by tower

"Newps" wrote in message
...
I was in position and holding on 34 at Asheville, NC (AVL) today, with a
plane on final, me in position and holding, and a 182 in front of me
taking
off. Before his wheels left the runway, I was cleared for take-off.

The rule is you cannot start your takeoff roll until the required
separation exists. He probably hurried your clearance because of the
plane on final. Having one single chase another down the runway is common
at any busy GA airport. Being 500-700 feet short on separation is a
trivial matter.

My local airport can get busy at times (reasonable amounts of GA, and we
share the airfield with everything up to 767s) but we don't get a lot of
"chasing down the runway". I've had a few "land after"s, but we've got
1,850m of runway and they're no problem (and anyway, it's only an invitation
that one can decline, not an order).

I've not had a take-off clearance when they guy in front still had his
wheels on the runway, but I _have_ had plenty when he was only a hundred or
two feet in the air. And the clearance was always of the form: "Departing
traffic is a C152 [or whatever] turning left on departure; with that traffic
in sight, cleared for take-off ...". I suspect the main thing the controller
needs to be thinking is not so much the formal separation distance, but the
consequences of two single-engine aircraft suffering an EFATO and having to
set down - the last thing you need is a runway with one small "obvious"
EFATO field at the end of it and two aircraft both heading for it at once!
In our case, if you hear the guy in front has a problem and is heading for
the "standard" bit of ground, you probably still have time to abort.

Another poster made the most important point, of course - namely that a
clearance to take off is not an order to do so. Only if you have lined up
under a "line up if able to commence immediate departure" do you have any
compulsion to get your skates on!

D.