Vikkyvik From United States of America, joined Jul 2003, 10350 posts, RR: 26
Reply 1, posted (6 years 7 months 3 weeks 5 days 17 hours ago) and read 1588 times:
Quoting Flyboyseven (Thread starter): How close could you put the end of a runway to a terminal so that the final is over the terminal? Is 3000' with another 2500' displaced threshold good?
Or, what is the minimum altitude for going over a terminal on final? Is 900' enough?
I suppose that it would depend, among other things, on the max height above the runway of the terminal (or the max vertical stab height of airplanes parked at the terminal).
Believe the FAA mandates a 1000' x 500' minimum clear area at runway ends. Then there's all the confusion of displaced thresholds, stopways, clearways, blast pads, etc. I've never quite been able to get my head around all of it.
But to give you a general idea, assuming a standard 3 degree glideslope and a 50 foot threshold clearance height, an airplane will be descending at about 50 feet vertical per 1000 feet horizontal (a 5% gradient).
So, at 1000 feet from threshold, an airplane would be at about 100 feet. At 2000 feet from threshold, it'd be at 150 feet. At a half nm from threshold, it'd be at just over 200 feet.
Obviously, obstacle clearance gradients will be more restrictive than a standard 3 degree gildeslope.