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Guest frankathl

When Is Flap Retraction Altitude?

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Guest frankathl

Thank you, Darren.I'd like to know if there is a published speed schedule specifically for the NG? I haven't seen one, as the FMC normally calculates the Vm speeds and displays them on the speed tape. The only speed schedules I've seen, so far, are the ones for the 3-4-500 series. Also, here is a quote from the Flight Manual re the NG aircraft:"Note: Due to a new wing and rudder design on these aircraft, flap retraction will be done at the VM speeds shown on the airspeed indicator after V2+ 15 has been reached."So, it seems the flap retraction speeds are calculated each time by the FMC according to the actual weight of the aircraft.BR,Frank

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Guest frankathl

Thanks TW! A handy QRC, indeed. These flap retraction speeds are for the Classic 737s, though.Please see my response to Darren, above.BR,Frank

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Guest BlackDog

Whoops, I thought these were for the 737 throught the 900 series. He mentions the various models by number in the QRC.

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Guest Darren Howie

G'day FrankYou will find like all transport catagory aircraft the flap retraction schedule is based on the V2 speed.This means every retraction schedule is weight based and the calculation is done bythe FMC.Hence when you pop in the numbers the fmc calculates the flap retract speed based on the weights you have programmed in.In smaller aircraft the flaps are extended and retracted generally at the same speeds on most flights but in larger aircraft it is weight dependant.Darren

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Guest boxjockey99

FrankI am a 300 driver so all my data is based on the 3-4-500 series aircraft. The NG does indeed have a new wing and rudder and uses the green 'F' on the speed tape much more than we do. As a young pilot I tend to use a bit of both in order to prepare myself for the day when we do get shiny new NG aircraft. On the 300 we have the speed tape with the green 'F' and 'O' so I tend to retract the flap by saying to myself 'we are past the green 'F' with speed trend increasing and we are withing a 10kt margin of the canned speed and above V2+20. If all of those are met then I call for the next stage of flap. So for example after a flap 5 take off when we are light the FMC may decide that 145Kt is the 'F' speed for flap 5 - flap 1. I would wait till we were 160kt with the trend increasing as the canned speed for 5 - 1 is 170kt. The NG is something I have yet to play with but I understand that they don't use canned speeds so in that case I would be waiting for a healthy margin past the green 'F'. This is mainly because the speed tape is based on the pitot/ static system and thus can flap around in the wind so if you don't have 10kt in hand the speed tape can suddenly be back below the green 'F' and could land you in a sticky situation.Hope that helpsKris

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Guest frankathl

Apologies, TW, you are, indeed, correct! I misread your flap speed table because of the formatting, then didn't read the QRC properly!:-( Bruce does indeed offer "recommended" speeds for the 7-8-9 series, which are the same as the speeds for the higher weight Classic 737s. Very useful, and I thank you!Normally, for the NG series, the flap retraction speeds are not fixed, but are computed by the FMC for the specific weight of the airplane. In that sense, the Classic speeds are more "ballpark".Best RegardsFrank

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Guest frankathl

Thanks, Darren, that makes sense. :-)BR,Frank

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Guest frankathl

Thank you, Richard!Yes, I do have access to that information.My point is this:737 Classics: Absolute(read:specific) flap speeds are given for the 3-4-5 series, as per your table, based on approximate aircraft weights, ie below 117,000 pounds/above 117,000 pounds. For example, Select Flaps UP at 190/200 depending on weight category.737 NGs:Relative(read:formula) flap speeds are given for the 7-8-9 series, eg,Select Flaps UP at Vm Flaps 1. That is, you are expected to use the FMC predicted flap retraction speeds, as annunciated on the PFD speed tape.As Darren pointed out, ALL flap retraction speeds are derived from V2.However, I was unsure what speeds you would use on the NG if you were NOT using the FMC.Note: TW has pointed out to me Bruce Sprague's very useful QRC which does give "recommended" flap retraction speeds for the NG series. I'm more than happy to use those(see T. W. Taylor's post above).I'll stop going on about this now, before I get a raft of ENOUGH ALREADY posts :-). Many thanks to everyone who responded. I've learnt A LOT!BR,Frank

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Guest BlackDog

"Normally, for the NG series, the flap retraction speeds are not fixed, but are computed by the FMC for the specific weight of the airplane. In that sense, the Classic speeds are more "ballpark"."I assume by this you mean the marks on the speed tape indicating flap retraction points. Am I correct in that assumption?

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Guest frankathl

Thanks once again, Kris, for such useful information!This will all get printed and put in my "How To" notebook.BR,Frank

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Guest Sjaako

Hi all,If the FMC would not be calculating any speeds, due to a failure for instance. You set the aircraft weight with the little turning knob to the left of the autobrake. above the engine indications panel.When you set this weight correctly you get all appropriate flap speeds on your speed tape.So there would be no reason to ever fly without any actual flap speeds.Regards, Sjaako

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Ok, sorry to interrupt the discussion but I need to backtrack a little here. I almost always use flaps 5 for takeoff and although I seem to read everywhere that we're supposed to select flaps 1 at V2+ 15 to 20, I don;t understand how this makes sense because I'm always reaching this speed almost immediately after rotating, say 100' AFE. In my opinion it wouldn't make much sense nor does it seem safe to start retraction at such height from the ground. Plus you keep climbing at this speed for usually over 1000 ft (till reaching thrust red and accel height), so why not climb at this speed with flaps 5? Furthermore, I read somewhere that we should select flaps 1 only when passing the flaps 5 maneuvering speed (which we all know is on the speed tape as a little green 5), and this usually only happens when reaching accel height. so, as you can see form my quite confusing post, I'm a confused little man regarding 737s and their flaps. I'm really starting to enjoy the simplicity of the Cessnas I fly! Cheers,Victor

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Guest frankathl

Yes, T,W., that's it. You won't know your actual Flaps Up speed until you've programmed the FMC and checked the tape(and, by the way, you won't be able to see the flap speeds on the ground because the speed tape will only show between 0 - 100 knots).In the Classic 737s, you have a lookup table(see Richard's mail just below), so, even if you have not programmed the FMC, you can still say, for example, that Flaps Up will be about 190kts for a airplane less than 117,000 pounds gross weight.I think this makes the NG flaps speed somewhat more precise as it may vary over the full range of airplane weight, instead of picking from a choice of two only(190 below 117,000, 200 above 117,000).BR,Frank

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