App Flaps Driven Speeds & Vnav

[crvm]

Question for you NG drivers,

If you are in VNAV on approach and are going through flaps driven speeds but happen to have a hard speed say of 160 /wpt and you select landing flaps prior to the FAF (I know folks wait) but say after you select APP REF flaps, should the FMS stay at the last flap speed OR command the last restriction speed of 160 prior to G/S?

I cannot find anything that states this plainly. I know on TO if (I know most do not do this if at all) if one selects VNAV prior to flaps retraction (say no noise procedure to worry about etc) VNAV will command *climb* target and the flaps speeds are ignored, this on the 800 NG but on some 300s like America Wests' the speed trickles only up to the flaps speeds and not climb target (250/10000).

I know this is not the way people do it but am interested in WHAT it will do in this case.
Thanks.

crvm

[crvm]

Thank you Chuck for the detailed answer sir.


crvm

[alexban]

ckuck:
you are right about what you take from manuals but I think crvm asked something different.
So if you select restriction 160 kts at OM what will VNAV command for speed?
210 at 12 NM ,then start selecting flaps.Assume select flaps 15 before OM. The speed for a classic should be 150 ,for NG somewhat slower.The max speed for flaps 15 is much higher than 160 for both types.
So what speed will the a/p keep before OM ? 150 or 160 ?
This is the question.
My guess it will keep 160 kts as it doesn't conflict with limits for existing configuration.Will try.
Brgds Alex

[alexban]

crvm:
as I said I'll do I've tried this today:
selected 160 kts restriction at OM at 4NM
in vnav,started to reduce speed at 12NM, selecting flaps.
Vref was 127.Correction 5
Selecting flaps 15 speed was 160 kt instead 150 as should have been for flaps 15
Further flaps -speed remained 160 ,with flap 30.
At GS capture the mcp speed window opened,indicating 160
In descent page active speed was 160
Only after OM,which had my 160 restriction,the speed in the descent page changed to 132kt
I hope this will answer your question.
Chuck's answer was correct,but it does not take in account a speed restriction inserted in FMC.
As I said chuck,I've selected flap 30-speed 127 in 4R app ref page,but the fmc kept 160 as I inserted at OM,even after selecting flap 30.
As long as this speed does not conflict with actual configuration ,this will be the active speed.
Brgds Alex

[alexban]

chuck ,the plane was a 300, software if I'm not wrong it's ver 10.4
I'm pretty sure on the 700 series it will be the same.The important thing it's to keep the restriction speed ,i guess,if you're in the envelope,of course.
If you're curious about the Ng i'll do this test on the ng also.
Brgds Alex

[crvm]

Thanks guys. Very interesting. I will assume the 300's FMC @ U10.4 will not be any different on any NGs running 10.4 but heck you never know with the NG.

What I find odd is that in TO mode in some 300s VNAV will not keep the 250 under 10 but insted stay at XXX/FLAPS until clean. Of course I do not hear any NG drivers going VNAV prior to flaps retraction for various reasons but the fact that in VNAV prior to clean the target jumps straight to 250 under 10 on the NG. Why they differ here I do know.


crvm

[alexban]

for 300 speed limit for flap under 10 is 230 kt ,compared to 250 kt for NG.
Maybe this is the answer to your question.