Any rule of thumb for Flaps Up Manoeuvring Speed?

[davidlondon 0]

In my efforts to perfect NADPs, I need to command VREF40+70 via MCP Intervention. FMC CDU provides V2 and V2 + 20 but not VREF40 for TO and climb (I think). Is there any way of finding or calculating VREF40 without resorting to the FCOM 1 manual - which is fine, but just not as easy as point-and-click? Thanks! Best wishes, David

[badderjet 181]

Hm maybe I'm lost what you mean, but actual V_REF40 should be displayed on APPROACH CDU page at all times during flight...? BTW V_REF40+70 is always flaps up maneuvering speed, so why don't you use that one on the PFD? It's there anyways. Accelerating after takeoff, "BUG UP". Should be pretty much V_REF40+70. No messing around with numbers in any way.

[davidlondon 0]

Etienne, Thanks. I am aware that VREF40 appears on the CDU during flight under APP - To be honest, I didn't yet look to see if it was there before TO. An oversight on my part? Best wishes, David

[davidlondon 0]

Oh ... and to explain about NADPs: As you may recall (and I hopefully recall correctly!) from Jack Colwill's excellent video ["Do You Really Need Speedbrakes VIDEO? Part 2"), the NADP 1 noise abatement procedure requires you to maintain [max] V2 + 20 with TO thrust, then at Cutback thrust from 800 AGL until 3000 AGL. At that point, N1 reverts to CLB (or CLB-1 etc) but I believe best practice says you have to keep MCP speed intervention engaged at VREF40+70 until flaps up - at which point you can re-engaged VNAV SPD, which would otherwise be 250 and not (say) 213 KTS ... Always happy to stand corrected by the professionals and the more proficient! Best wishes, David

[Cristi_Neagu 134]

Why don't you follow the flap speed bugs on the speed tape. It'll show you where flaps up speed is.

[badderjet 181]

Why don't you follow the flap speed bugs on the speed tape. It'll show you where flaps up speed is.

Yes, that's what I practically said above. I understand you want to fly the NADPs correctly, but as far as speeds go, whether you start accelerating for flap retraction at 800, 1000, 1500, 3000 or anywhere in between, I believe standard procedure is "BUG UP", which means to select MCP speed to the "UP" indication on the speed tape. As you accelerate through V₂+15 and the respective flap maneuvering speeds thereafter, you retract the flaps. No math req'd at all, and certainly no V_REF. I never heard anyone even mention or think about V_REF for anything takeoff related. You are correct, UP speed is based on V_REF, which again is based on GW, but who cares. As long as the weights in the FMS are entered correctly, you don't have to mess around with the numbers. If you had VNAV armed before takeoff or use it during the departure, it will even do everything for you. I don't think SPD INTV is req'd in this case. Basically it will maintain V₂+20 until acceleration altitude as set on TAKEOFF page 2/2, then accelerate to either 250 if climb speed restriction is set, climb speed if without speed restriction, or max placard speed for current flap setting (roughly guessing on that part rough, at least it wouldn't shoot thru the red bar). That should be it. EDIT Oh, and BTW I do believe you could see the APPROACH page before takeoff, by just going to the INDEX and selecting it from there. Was that your problem? Would have to check though if the speeds are there already while still on ground, but I wonder why they shouldn't. Will check it out however. But as I said, should never be needed for takeoff.

[Spin737 102]

Yes, that's what I practically said above. I understand you want to fly the NADPs correctly, but as far as speeds go, whether you start accelerating for flap retraction at 800, 1000, 1500, 3000 or anywhere in between, I believe standard procedure is "BUG UP", which means to select MCP speed to the "UP" indication on the speed tape. As you accelerate through V₂+15 and the respective flap maneuvering speeds thereafter, you retract the flaps. No math req'd at all, and certainly no V_REF. I never heard anyone even mention or think about V_REF for anything takeoff related. You are correct, UP speed is based on V_REF, which again is based on GW, but who cares. As long as the weights in the FMS are entered correctly, you don't have to mess around with the numbers. If you had VNAV armed before takeoff or use it during the departure, it will even do everything for you. I don't think SPD INTV is req'd in this case. Basically it will maintain V₂+20 until acceleration altitude as set on TAKEOFF page 2/2, then accelerate to either 250 if climb speed restriction is set, climb speed if without speed restriction, or max placard speed for current flap setting (roughly guessing on that part rough, at least it wouldn't shoot thru the red bar). That should be it. EDIT Oh, and BTW I do believe you could see the APPROACH page before takeoff, by just going to the INDEX and selecting it from there. Was that your problem? Would have to check though if the speeds are there already while still on ground, but I wonder why they shouldn't. Will check it out however. But as I said, should never be needed for takeoff.

+1 If you're doing NADP1, just takeoff with VNAV armed and start cleaning up at 3000'AGL. That assumes you've preflighted the CLIMB page to match.

[davidlondon 0]

Thanks, everyone, for your thoughts and advice. Need to take a little more time than I have tonight to digest and apply in practice - so this is a courtesy note for the present. Will return with feedback back soonest. Meanwhile just +1 re Matt's recent note: Yes, I have been arming VNAV just fine - but looking through the legs for my particular route (LFPBLFMN), it looked as though VMC SPD *might* increase beyond Flaps Up Manoeuvring *before* I had reached 3000 AGL. Maybe I'm dreaming and this would never have been the case, but that was why I came up with the idea of MCP Speed Intervention - especially having seen Jack's video, where he stays with MCP SPD until flaps up. Based on your collective advice, I'll check this again and take a look at all the things you recommend. Forgive me: must be off now! Best wishes, David

[Spin737 102]

Thanks, everyone, for your thoughts and advice. Need to take a little more time than I have tonight to digest and apply in practice - so this is a courtesy note for the present. Will return with feedback back soonest. Meanwhile just +1 re Matt's recent note: Yes, I have been arming VNAV just fine - but looking through the legs for my particular route (LFPBLFMN), it looked as though VMC SPD *might* increase beyond Flaps Up Manoeuvring *before* I had reached 3000 AGL. Best wishes, David

The acceleration altitude on the climb page is there exactly to control the issue you reference. The aircraft accelerates from V2+20 when it climbs past this altitude. If you're performing an NADP1, the jet will climb at V2+20 until 3000agl, and then it will accelerate. It will command a speed of 230 until the LEDs are retracted and then 250 until 10,000. Those numbers also assume the Climb page is preflighted that way. In the US, many airlines use NADP2 as the standard, and will set up the climb page differently to reflect the differences in procedure. This assumes U10.8+ where VNAV can can be armed for T/O.

[davidlondon 0]

Etienne,Matt, Well, OK, I did my homework and practice just now - and your advice made perfect sense. Thanks for your patience and your time in explaining things. I'll be having a go at a NADP 2 soonest too! Best wishes, David And, yes, as you suggested: if you ever needed it, VREF40 is right there on the APP page before you take off ...

[badderjet 181]

Great it worked out for you! Have fun.