Lining up allowance for take off performance
 

Does anyone know the allowance included in take off performance for the lining up proceedure. I seem to remember it is in the region of 23m, but would be grateful for any references.

It's aircraft dependant, not a fixed amount.

FAR 25 will give you no help at all, whereas JAR will give you a good 'tool' for determining the value. More than likely, aircraft certified under JAR will have the line-up allowance already factored in to the AFM data, whereas FAR 25 certified aircraft will not.

Regards,

Old Smokey

Its aircraft specific as Old Smokey has stated, we have aircraft with 10 meters and 57 meters.

Not required by FAA but required by JAA and Mutt.....


Mutt

Many thanks to you both.

The loss of runway length due to alignment is required by JAR-OPs 1.490 and an acceptable means of compliance is laid out in IEM Ops 1.490. Accountability is required for a 90 degree taxi entry or a 180 degree turnaround eg when backtracking.

The IEM has a calculation for working out the loss of runway and its dependant on the radius of turn of wheels, wheel base steering angle etc.

Performance figures usually comment on which alignement accountability has been used.

Hope this helps. Although the text of JAR Ops 1 is on the JAA website I don't think the IEMs are.

... but required by JAA and Mutt..

... and JT and OS ...

Oz was probably the first to worry about lineup .. (scratches head) probably 30 years or more ago ? ... I still have copies of the Qantas/DCA correspondence on the original philosophies somewhere on file ...

Qantas uses 65 metres for the 747.

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.

http://www.geocities.com/profemery/c2.jpg

http://www.geocities.com/profemery/c3.jpg