T/Oshift of 747-400 FMS

[waypoint5944]

Hi!
If the T/O rwy has the landing threshold and the displaced threshold(longer rwy than landing),which one is the "0"shift position?
For example, the total length of the LAX rwy 25R is 12,091ft and the length available for landing is 11,045ft. When we want to use full length for T/O , do we have to put
"-10" for T/O shift on the FMS T/O reference page?
But in our company "airport analysis chart"the lengths of the rwys are always the full length available for T/O(12,091ft 25R of LAX).I think FMS has the Performance database which includes the lengths of the rwys. I think the rwy length of the of FMS and "AIRPORT ANALYSIS CHART" should be the same.
Somebody told me the baseline for take-off shift is always the landing threshold. I couldn't find that kind of words from my manual.Somebody tell me where it is.
Thank you.

[Balthazar]

I believe that the 400 uses the T/O threshold for the position shift. That means that if only the landing threshold is displaced it won't have any effect when the TOGA buttons are hit. So if T/O is from the normal position, generally full length, then you don't need to do anything.

If you go to the APPROACH REF page the runway distance that is in the database is displayed. This is a good check.

I must admit that I am only explaining what I do. I just checked my Honeywell manual and it is really quite vague.

I may be wrong, and if so I hope that someone who knows better can elaborate.

Cheers.

[mustafagander]

According to the brown FMC Users' Guide, page 7.11 the landing threshold is what's in the nav database. So if it's a displaced threshold - adjustments may apply.
LAX 25R is -10 for example. If your a/c has GPS coupled into the FMS the pos shift is irrelevant - disabled actually.

[waypoint5944]

So that T/O shift only affect the position of the a/c. I think it also affects the T/O performance. If we reduce the rwy length by putting "10" on the t/o ref page it will reduce the V speeds to adjust the performance.
Right?

[Balthazar]

If both distances are in excess of the balanced field requirements, then the V speeds will be unchanged.

[Cornish Jack]

The 'Pos Shift' line entry is just a position updating function. If you are (for example) using a displaced threshold for take-off, or an intersection rather than full length, the distance from the normal threshold is entered in hundreds of metres on the 'Pos Shift' line. Having done so, when the TOGA switch is pressed the FMS will position update to that revised position rather than the usually defined runway threshold. Gives a more accurate starting point for subsequent navigation.