VNAV departure problems

[Boeing_Captain 0]

Hi guys,I seem to be experiencing problems with my departures when using VNAV under autopilot control. For some reason, the aircraft always seems to break though the flap retraction speeds. The auto throttle system doesnt seem to reduce the engine thrust to maintain the flap retraction speed, it just goes straight past it. So, by 3000ft, im in the full clean configuration and well on my way to 250kts. Before I installed the 800/900 package, the 600/700 seemed to hold the flap retraction speeds fine. Now however, none of them do. I have the auto throttle armed prior to departure, so I know its not because the auto throttle isnt active. I use reduced takeoff and climb thrust, but even using full takeoff and climb thrust, it still breaks through the flap retraction speeds.Any ideas ?Thanks in advance.Regards,Lee Holland.

[falcon999 24]

Hi Lee,Are you using TO/GA mode for takeoff?

[crvm 0]

the aircraft always seems to break though the flap retraction speeds What ever do you mean by "flap retraction speeds"? FYI MAXIMUM flap speed for flaps 5 is 250 KNOTS! Do I need to say more? [h4]Best Wishes,Randy J. Smithhttp://www.precisionmanuals.com/images/forum/betaimg.jpgAMD 64 3200+ | ASUS KV8 DELUXE | GFORCE 5700 ULTRA @535/1000 | WD SATA 80 GIG | 512 DDR 400 |

[Boeing_Captain 0]

Hi guys,Thankyou for your quick replies. Randy, im a bit shocked at your reply to be honest. I've probably only posted on this forum three times at the most, and from reading your reply, you seem to be very abrupt as though your treating me like an idiot. Being a seasoned PIC driver, im not that by far. By flap retraction speeds, I mean the small green annunciations on the speed tape of the PFD when your departing. If your at flap 5, then it will annunciate "2", "1" and "up" up the right hand side of the speed tape telling you when you should retract your flaps.With the original 600 and 700 package, climbing out at flap 5 for instance, when the speed reached the small green annunciation "2", the thrust would reduce to hold the speed adjacent to "2" until I selected flap 1, then the thrust would increase and then hold the next speed until I brought the flaps all the way up, then it would accelerate to 250kts.However, it doesnt do this now. It just seems to want to go to 250kts straight away. Surely this isnt right ? Regards,Lee.

[Guest Sunnyzsz]

Which reminds me, what altitude do most of you engage VNAV and LNAV? Vnav for me is 1,500ft and LNAV is normally around 2,000ft

[Guest norwegian]

Flap retraction speeds are shown on the PFD where the takeoffspeeds (V1, Vr and V2) are shown. It is a tiny green line showing the flap retraction areaon the PFD like this: --1 (which means flap to one after passing this line, just like V1, VR etc..)I've got the same problem too, the VNAV accelerates up to 250 KIASbefore you take the flaps up?!? Before the 800/900 came out the 600/700 versions was workingperfectly on this speed adjustment!What happens is that when you establish positiv climb (gear up etc..)and push autopilot on and LNAV and VNAV, the VNAV is supposed tohold the speed under 200, depending on weight, when you have flapsat 5 degrees angle. This means that when you retract the flap from 5 to 1 deegrethe VNAV is supposed to accelerate up to the max speed forflap 1 setting, not up to 250 KIAS, which it does now!And when you retract the flaps fully up, the VNAVthen accelerates up to 250 KIAS and holds until passing 10000 feet.This is probably a little bug in the new 800/900!

[Guest norwegian]

CRVM wrote:FYI MAXIMUM flap speed for flaps 5 is 250 KNOTS! Do I need to say more?well,, if you want to be abit realistic flying the 737NG,NO PILOT in the real world would have 5 degree flapson takeoff up to 250 KIAS!! Yes it is possible to fly that fast with flaps 5 setting butin the airliner industry you must NEVER push thingsto the MAXIMUM unless it's nessecary!!

[Boeing_Captain 0]

Hi Norwegian,Apologies, but im not sure what your real name is. Im glad to know that somebody else is having this problem. At least it isnt me just being stupid like Randy's reply to my original post seems to imply.I knew it worked prior to the release of the 800/900 package. Im surprised nobody else has mentioned this already. Oh well, everybody else must think its completely normal to fly at flap 5 until 250kts.I certainly dont. Glad to see you agree with me here mate.Thanks,Lee.

[Guest norwegian]

Sure i agree!I've never seen a 737 fly in 250 KIAS with flap 5 setting,and try reading the manual, cant find any FLAP 5 = 250 KIAS!!and i too know that before the 800/900 models came outthis VNAV adjustment for flaps was working perfectly!Glad to help :)Yngve (is my real name)

[Guest HepburnUGA]

I am having this problem as well...My general procedures are to set up the climb page as follows prior to departure:Target speed = 250ktsSpeed Restriction = 210/3000I will then engage VNAV @ 1000ft and set flaps 1. Approaching flaps 1 I will set flaps 0. This profile will complete the climb to 3000 feet at Vm flaps up and then accelerate to 250kts.Well, when I engage VNAV at 1000ft and set flaps 1, the speedbug automatically goes to 250kts.

[zubart 5]

Its doing what it should do, its in TOGA mode.If you are pushing TOGA for takeoff the autothrottle maintains takeoff N1 thrust limit as selected by the FMC. To get the desired response that you want, select LEVEL CHG above 400 feet RA and the airplane will hold the airspeed at the time it is selected. This is probably not a standard takeoff proceedure in the NG. Read a tutorial.Floyd

[Guest norwegian]

No, it's not supposed to happen. when an aircraft is in TOGA modeit will automaticly hold speeds on restriction.say for instancethe flap is set at 5, an electronic sensor called a CX engine(a tiny DC engine used in larger aircrafts) gives a feedbackon flaps, slats, ailerons, rudder and trim.this feedback is given to the computers and FMC etc...This engine tell the computers if anything is wrong.mainly it's used to give feedback to the computer.Therefore, when an aircraft is in TOGA mode it is only supposedto give the desired thrust for takeoff and then hold speeds at climb out from the airport.because this little engine tells the computer to stay at a recommended speed for any flap setting right after takeoff.and absolutely not go straight to 250 KIAS when flap isset @ 5 or similar.Thats how it was in the 600/700 where this function was workingproperly.

[Guest HepburnUGA]

The procedure that I use come straight from Bill Bulfer's FMC manual. Yes I agree that TOGA commands N1, but you are overlooking the fact that the AP will use attitude to control speed. When the aircraft reaches the target speed, it will pitch up to maintain that speed. I stand by my original stance that something is not working as it should.

[Guest Zapper]

HMM..Gents I think the problem here is the gap between the real world and the sim world. May I offer a small guide I have written for real world pilots new to the type available under the 737 Info section at: http://homepage.powerup.com.au/~speedy/ or better yet read it direct here at: http://homepage.powerup.com.au/~speedy/737...ific%20Blue.docFirst off the speeds shown for each Flap position are NOT retraction speeds, they are FMC computed speeds that provide a manoeuvring margin at that flap setting ie you can roll to a 30 degree bank with a 15 degree overshoot in level flight and not have the stick shaker go off. So each of these speeds is called the Flap 'x' Min Manoeuvring SpeedThat said:IRL we will normally take off in LNAV and TOGA. LNAV will be selected during the pre-flight set-up of the MCP and TOGA will appear when you tap the TOGA buttons to start the takeoff roll.In the companies I have flown with we do NOT use VNAV for takeoff and I will check if it is available at all in the 737 NG.After takeoff we will climb in TO/GA which will command the autothrust and pitch modes to give the selected takeoff thrust and a pitch attitude to hold the MCP selected V2 speed up to V2+20.We climb at this speed to Flap Retraction Altitude (in most places about 3000' AGL for noise abatement) and we then do what is called 'Bugging Up' ie the MCP speed is set to the Minimum Clean speed. This causes the Flight Director to command a pitch down to about 10 degrees and the aircraft to accelerate.As the aircraft accelerates though the Flap 5 Minimum Manoeuvring Speed we select Flap 1, on accelerating through the Flap 1 Minimum Manoeuvring Speed we select Flaps Up.When the flaps are up and no lights showing the PNF will select the Gear Handle to OFF and the Autobrake switch to OFF. Only then will the aircraft be accelerated to climb speed in either VNAV or MCP Speed, generally 250kts below 10000'. The reason for this is so that should the PNF inadvertently select the Gear Down you will not be above the maximum extension speed for it.This enough info? Hope it makes things clearer rather than muddy the waters further.Rgds,Brad Marshhttp://homepage.powerup.com.au/~speedy/pic...Hawaii_Crew.jpg

[Guest norwegian]

Yes, better to hear this explained by a pilot rather than a mechanic!i only fix the aircrafts, but i can hear with the avionicsat work and see what they have to say!Brad wrote:In the companies I have flown with we do NOT use VNAV for takeoff and I will check if it is available at all in the 737 NG.Ofcourse not, VNAV is engaged after takeoff.BUT: no aircraft whatsoever in VNAV mode will push theaircraft to speed up like it does with the PMDG's 737.when the flaps have not been retracted.it's just as if it was to speed up the aircraft to go beyond 270 KIAS with gear extended.but it is just the difference between sim and reality.it's just a pitty that this function is not working anymore.