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748 / 744NG FMC: Takeoff data uplink

Started by Hardy Heinlin, Sat, 11 May 2019 11:45

Hardy Heinlin

Hello,

is there any real 748/744NG user on board whose airline somtimes (or always) uplinks "alternate" takeoff data?

When a data uplink is pending, the (new) TAKEOFF REF 2/2 page at 1L provides a selection key for ALTN/STD THRUST/FLAPS etc. -- And in 6R there are options for STD/ALTN LIM TOGW.

Unfortunately, the usual Boeing and Honeywell manuals don't describe these functions in detail.

Has anyone used these features on the real deck?

As far as I understand it, the company may uplink two sets of takeoff reference data.
Each data set consists of:

(a) Takeoff flaps
(b) Takeoff thrust setting
(c) Ref OAT
(d) Takeoff wind direction/speed
(e) Takeoff crosswind/headwind
(f) Slope and wet/dry condition
(g) EO ACCEL HT
(h) ACCEL HT
(i) THR reduction point
(j) Limit takeoff weight

My current theory:

When there are two data sets, both data sets refer to the same takeoff runway and threshold (which were set before requesting the uplink). There is never one data set for one runway and another set for a different runway. Correct?

When there are two data sets pending, they only differ in any of the above parameters (a) through (j). Correct?

The currently displayed data set refers to the thrust setting on page 1/2, e.g. "38° D-TO". On page 2/2, line 1L may indicate, for example, "ALTN THRUST, <TO-1"; when I select this, the second data set will be displayed, that is: Page 1/2 will display "TO-1", and 1L on page 2/2 will display "STD THRUST, <38° D-TO". Correct?

When do airlines provide two different data sets? Is this helpful when there is a great risk of a delayed takeoff, say, 20 minutes, and the wind will most likely change in 20 minutes, for example? (And the takeoff weight will be lower if the engines keep running.)
Or is it helpful if the ATC clearance (SIDs with different obstacles) cannot be determined yet?


Thank you!

|-|ardy

Jeroen Hoppenbrouwers

It *may* be that "alternate" only refers to "alternate takeoff thrust" while everything else is the same. This would give one variable that the crew can still play with.

http://www.theairlinepilots.com/forum/viewtopic.php?f=32&t=747


Hardy Heinlin

Maybe it's just that. But I would add at least 2 more variables: flaps and weight.

Page 2/2, LSK 1L line title may read:
• STD THRUST
• STD THR/FLP
• ALTN THRUST
• ALT THR/FLP

Page 2/2, LSK 5R line title may read:
• STD LIM TOGW
• ALTN LIM TOGW

On the other hand, if the thrust is to be changed, the V speeds need to be changed as well. So you'll get some more changes in any case.


|-|ardy


Note that your link refers to the 777 which has the above functions in 2L and 4R.

Hardy Heinlin

Independent of the FMC question, here's a general question: -- Are there situations when dispatchers provide a takeoff data set for flap 10 and another data set for flap 20, and the captain may then decide what flap setting is currently appropriate?


|-|