tappan
Posts: 1478
Joined: Sat Oct 23, 1999 9:30 pm

WhatIs"DisplacedThreshold"OnFinal?

Mon Oct 09, 2000 9:08 am

Boston tower tonight squeezed in a 737 landing on Runway4R seconds after a 747 took off on same runway. Tower said to the 737 ""Displaced Threshold" in effect clear to land....What is that???Anybody know???
Thanks
 
cylw
Posts: 407
Joined: Sun Apr 09, 2000 2:34 pm

RE: WhatIs"DisplacedThreshold"OnFinal?

Mon Oct 09, 2000 12:31 pm

A displaced threshold is where for some reason they need to move the threshold further down the runway. Possibly there was damage to the first part of the runway, or there are temporary (or permanent) bstacles on the normal approach path that warranted moving the of threshold. My KBOS chart shows that 4R is displaced a little bit down the runway from taxiway Sierra.

Hope this helps

Matt
 
Purdue Arrow
Posts: 947
Joined: Tue May 25, 1999 1:49 pm

RE: WhatIs"DisplacedThreshold"OnFinal?

Mon Oct 09, 2000 2:19 pm

Actually, a displaced threshold is a little different than that. While displaced threshold does mean that the threshold of the runway, or the beginning of the usable runway for landing, is moved from the edge of the concrete, it is not due to problems with the runway surface. A displaced threshold generally keeps airplanes a little higher that approaching for the very beginning of the runway, so a landing plane can clear obstacles in the normal approach path. At the Purdue Airport in Lsfayette, IN, for example, we have a displaced threshold that keeps aircraft higher than the height of a freight train when we cross the railroad tracks just before runway 23. The area before the displaced threshold can be used for takeoff, but is not usable for landing.