When Is Flap Retraction Altitude?

[Guest frankathl]

I am prompted to ask this question again despite(read

[crvm 0]

Flap retraction1] Sometimes based upon PROCEDURE i.e. dependent on NOISE ABATEMENT regulations for the particular airport.2] Without that restriction I believe COMPANY POLICY i.e. SOPS or PIC choice under the situation at hand and of course speed is not too much a concern since max flap retraction for 5 is 250 knots, flaps speeds are limiting speeds not maximum speeds. I know that at times some NG pilots on a flaps 5 takeoff will at reaching V2+15 RETRACT to flaps 1 and wait till retraction altitude to fully retract, again depending upon the above.[h4]Randy J. Smith[/h4]

[Guest frankathl]

Thank you, Randy!"flaps speeds are limiting speeds not maximum speeds"If I understand you correctly, by "limiting speeds" you are referring to "flap maneuvering speeds", whereas "maximum speeds" are "do not exceed" speeds for a particular flap configuration?"I know that at times some NG pilots on a flaps 5 takeoff will at reaching V2+15 RETRACT to flaps 1"Just wondering if this could lead to problems, where you're at flaps 1 at 500'AGL and lose an engine? I think it was Kris Heslop who pointed this danger out in a previous post.Back to my initial question, though! What do NG pilots learn in training school about this topic? Presumably, while Continental pilots learn Continental SOPs, SouthWest learn Southwest SOPs("VNAV?" "Naw, you won't need to concern yourself much with THAT!"), etc, they must surely also be given GENERAL guidelines in addition to these, or it would make the subject impossible to study(or teach)? Putting this (yet) another way - quite apart from airport regulations, company policy, Standard Operating Procedures, or PIC's choice, doesn't the NG have a 'normal' climb profile described somewhere by Boeing, which acts as a baseline for all the other scenarios?BR,Frank

[zubart 5]

Frank,Here's my 2 cents worth,I would use 1000 feet AFE for the normal thrust reduction and flap retraction. The FAA minimum flap retraction is 400 feet AFE.After a engine failure it might be advantageous to start retracting flaps at 400 feet AFE if terrain is a factor. But I would say the typical acceleration/flap retraction altitude after an engine failure is 1000 feet AFE.Noise Abatement The company usually dictates what the first acceleration height to initiate thrust reduction and flap retraction. For noise abatement considerations during line operations, thrust reduction typically occurs at 1500 feet AFE and acceleration typically occurs between 1500 and 3000 feet AFE, or as specified by individual airport noise abatement procedures. For example, CYVR's noise abatement procedure is to climb at V2+10 to 20 to 1500 feet and reduce thrust to climb power and continue the climb at V2+10 to 20 to 3000 feet then retract flaps and accelerate to normal climb speed. At KSNA, the noise abatement procedure is quite different. Before takeoff, a "Cutback" is put into the FMC on TAKEOFF page two. The takeoff is to climb at V2 +20 to 800 feet AFE where the cutback automatically reduces engines thrust by about 20% on light airplanes and about 10% on heavy airplanes. Then the climb is continue at V2+20 to the restore altitude usually 3000 for heavy airplane and 4000 feet for light airplanes where climb power is automatically set by the FMC and the airplane is accelerated and flaps retracted. Floyd

[WAD3 0]

I have wondered this also. I have seen the many different answers and they for the most part make sense. I figured I would just do it my way and it has worked well for me. I fly V2+20 until 1500' rad alt and then lower pitch and retract on schedule. Like I said this is strictly Andrew Air policy. LOL

[Guest GeoffC]

Frank,Rather than answer your question personally I would like to point you at someone who flies these things for a living. Bill Bulfer produces some excellent books intended for RL drivers on the Boeing FMC's and systems which are a must for the sim owner of this aircraft if funds allow. They can be purchased from:http://www.fmcguide.com/Ok that bit is probably old news, but on the same site are some useful and more importantly free PDFs, including one on profiles which covers this topic. It can be found on this page under the profiles link:http://www.fmcguide.com/support.html

[Guest frankathl]

Hi Floyd,Thank you for a lot of interesting information!I did not know that 400'AFE was an FAA minimum altitude for flap retraction but, incidentally, I have since learned that the takeoff profile mentioned in Marc Brodbeck's article is actually a FAR requirement(it specifies a climb gradient for each segment of the climb, which Marc also describes)."After a engine failure it might be advantageous to start retracting flaps at 400 feet AFE if terrain is a factor."Would flaps down improve climb because of extra lift, or would they degrade climb rate because of drag? I'm confused here(not for the first time, either!). See also next pargraph.Very interesting examples from CYVR and KSNA, and great detail! As i understand it, the reason for the late flap retraction is to allow the aircraft to climb quickly when in the immediate vicinity of the airport(normally, a radius of about 2nm)for noise abatement purposes?BR,Frank

[Guest frankathl]

Thanks, Andrew.Yes, I'm sure there are many different possibilties. Was just wondering if some guidlines could be laid down so that we would have a sort of template to work from.BR,Frank

[Guest frankathl]

Thanks a lot, Geoff!By coincidence, I bought Bill Bulfer's FMC User's Guide last weekend, and, believe me, there is a LOT of information in there!I really like the 737 profiles and, yes, indeed, there is a recommendation to retract to flaps 1 at 1000' AFE(Flaps up at Vm1)! I must confess I had forgotten about that. Thank you!By the way, page 15, Pitch 'N Power has a very interesting diagram of the Takeoff Pitch Profile.Cheers,Frank

[Qavion 19]

>Would flaps down improve climb because of extra lift, or would they degrade climb rate because of drag? I'm confused here(not for the first time, either!). It can be a confusing issue, Frank. Flap settings affect obstacle clearance at various distances from the runway. Large flap settings allow a short term gain in altitude to enable you to comply with noise abatement regulations and to clear obstacles close to the end of the runway (buildings, etc), but smaller flap settings allow better climb rates over the longer term to allow you to clear obstacles further away from the airport (such as mountains). Usually you get to decide prior to takeoff which is the most important. Engine failure, of course, doesn't afford you this luxury (you have to juggle the two considerations as events unfold).You are correct in mentioning lift and drag. Having too much flap creates extra drag which ultimately keeps your airspeeds low, which means you will accelerate more slowly (and not get the extra air under your wings fast enough to provide you with more lift).Hope this makes sense.Cheers.Ian.

[Guest frankathl]

Makes a lot of sense, Ian!Thanks for the very useful and interesting information.BR,Frank

[Guest boxjockey99]

In my company we use 2 techniques for take off / climb phases depending on the noise sensitivity of the runway in use. The standard departure (where noise is not an issue) is using flap 5 as performance data allows and derating the engines in the appropriate manner where applicable. On positive climb the gear is raised and passing 400ft rad alt LNAV or HDG SEL is engaged. Passing 1000ft above the airfield we select VNAV and accellerate retracting the flaps on schedule. in bullet points this looks like+ive rate = GEAR UP400ft + LNAV / HDG SEL1000ft = VNAV170kt = Flap 1190kt = Flap 0Where noise is an issue we use the standard ICAO noise procedure which is as above for gear and engageing LNAV/HDG SEL but we delay thrust reduction to 1500ft AFE at which point we use N1 to reduce to climb power but maintain V2 - V2+20 until passing 3000ft AFE. At 3000ft AFE we engage VNAV and accellerate retracting the flap on schedule. in bullet points it looks like:+ive rate = GEAR UP400ft + LNAV / HDG SEL1500ft = N1 (gives climb power but doesn't command accelleration)3000ft = VNAV170kt = Flap 1190kt = Flap 0Our company seems to be alone in its use of VNAV prior to flap retraction so if you are uncomfortable with that then use LVL CHG and select 250kt to accellerate.

[crvm 0]

I wonder why that is the case Kris? I mean the FMC UXXX software is the same for the birds (most cases) so why the NG is different is beyond me. It makes sense that the FMC could limit to the next flap speed as a speed restriction.[h4]Randy J. Smith[/h4]

[Guest frankathl]

Great stuff, Kris! :-)Thanks for the clear and comprehensive information.Which 737 version is this for, please?BR,Frank

[Guest Darren Howie]

From most of my reading and experience it seems most Boeing aircraft are flown in terms of profile in a relatively similar way.With accel height/climb thrust being 1500AGL in most aircraft used and engine out accel at 800AGL a Boeing standard.Accel height will get increased to 3000' for noise abatement or by special procedure and may be higher or an intermediate altitude.So in simple terms its V2+10 or so to accel height then lower the nose to accelerate and retract flaps on speed schedule until they are up.This is the system we use on the 717 and is pretty much in line with that of the 73.Darren