747 FMC Take-off Question

[Guest castleberg]

Hello After having read the AOM and the Type rating course no.2 I'm still confused in one aspect of the CDU's Take-off Ref page. LSK 1L shows the flaps retracting altitude. LSK 3L shows the thrust reduction altitude. Both can have a value in feet AGL. How are those two values connected. In my understanding both should show the same value, i.e. flap retraction no sooner than thrust reduction. Or the other way: Only after selecting climb thrust flap retraction starts. Thanks for your help, Pilots. RegardsTom

[cowpatz]

Normally they are the same although they could be different dependant on the noise abatement procedure being used. From memory one of the procedures uses cutback thrust which occurs at a lower value than the flap retract height and this is where that would be entered. Also LSK 3 can accept a flap setting ie. entering a value of 5 will cause climb thrust to be selected when the flaps reach the F5 position.CheersSteve

[Guest castleberg]

Thank you, Steve. That will do it. RegardsTom

[cowpatz]

For your info we use 20/1500 1500 and 1500 although on occassion we use flap 5 as the climb thrust setting (out of LAX on a LOOP3 departure which has some high alt constraints to meet). The only time we use a flap setting other than 20 is for a number 1 or 4 hyd pump problem. For that we use Flap 10. This gives a better climb for the first 2 segments of the TO if there should be an engine failure. This is due to the slow retraction of the gear with a pump u/s and the subsequent extra drag and it's effect on the 3 eng climb gradient.CheersSteve

[Guest D17S]

My understanding was that LSK 1L provides the FMC with two separate pieces of information. "XX/YYYY." The XX was the takeoff flap setting that the FMC would then use to provide the final piece of info to calculate the V speeds. The FMC already had the runway and the weight from other pages and was just waiting for the crew to tell it what TO flap setting to use. Notice that as soon as you provide the TO flap data, the FMC immediately loads the Vspeeds on the right.The YYYY is the acceleration altitude: The FMC will flight direct the initial climb at V2 in TOGA pitch mode, then V2+10 after Vnav engages (with potential adjustments for this and that). This is to provide the maximum rate of climb at the minimum, safe, engine-out airspeed. This minimum, safe engine-out airspeed is V2. Needless to say, you don