Originally Posted by
Capn Bloggs
On the subject, it does seem a bit odd that there is a 10nm limit from a fix that in all likelihood the crew has no displayed distance to it (unless they had a GPS-updated FMS). It would be much simpler to have the limit based on the DME.
Scratching my head here. It would be based on the DME. the IAF is at D5.0 and remaining within 10 NM of that fix would be D15.0 approximately, technically being at D15.0 right at the furthest point on your PT would put you
slightly farther than 10.0 nm from the D5.0 fix because the distances aren't all on the same line. But that wouldn't be enough to be operationally significant. Normally procedure turn limits are referenced to the IAF.
Originally Posted by
Capn Bloggs
Thread Drift: why would there be a 15DME (10 on 5) limit on the proc turn? Doesn't seem to be any limiting obstacles...
Well, all procedure turns have
some maximum distance established. The normal procedure turn distance from the IAF is 10 NM (unless there is a need for something different) so procedure turn protected areas are established for obstruction clearance out to 10 nm, plus a stepped and tapered buffer margin. Obviously in this case you could go 100nm in that general direction and not find anything higher than a ship's mast. But, the normal procedure is to evaluate obstacle clearance for a PT with 10 NM of the IAF, and unless the approach designers need the additional distance for some reason, why expand the normal protected area when it's not needed? I think it's not that there's a specific reason (like high terrain) limiting the PT distance, but just that's the extent built into the design of the approach and "beyond here be dragons".