I remember reading about this the other day in the excellent Airbus document: "
Getting to grips with aircraft performance". To paraphrase from that excellent document:
Airplanes typically enter the takeoff runway from an intersecting taxiway. The airplane must be turned so that it is pointed down the runway in the direction for takeoff
[I do love the pragmatism of these technical writers]. FAA regulations do not explicitly require airplane operators to take into account the runway distance used to align the airplane on the runway for takeoff. On the contrary, JAA regulations require such a distance to be considered:
JAR-OPS 1.490
(c)(6) […] an operator must take account of the loss, if any, of runway length due to alignment of the aeroplane prior to takeoff.” Lineup corrections should be made when computing takeoff performance, anytime runway access does not permit positioning the airplane at the threshold. Runways with displaced takeoff thresholds, or ample turning aprons, should not need further adjustment. Accountability is usually required for a 90° taxiway entry to the runway and a 180° turnaround on the runway. The following tables (C2 and C3) contain the minimum lineup distance adjustments for both the accelerate-go (TOD/TOR) and accelerate-stop (ASD) cases that result from a 90° turn onto the runway and a 180° turn manoeuvre on the runway.
