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victorlima01

Please help me descend!

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Hi guys, so far I've had no trouble whatsoever with my 737s, everything works perfectly well. Yesterday however, I tried to fly a short route which I'm quite familiar with and ended up having problems. I would like to request tO everyone who's interested to try out and reproduce this quite interesting flight and see if you come up with the same results as I did.The flight is a short one from S


Cheers,
Victor M. Lima
 

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Ok... maybe noone's interested in flying this route. But either way can anyone help me understand why the heck I can't descelerate during descent and why in the world am I climbing and descending at only abou 1500 fpm???? If I try to go up faster I have to maintain very low airspeed (i.e 260 KIA above 10000') and in the same token vnav is descending way too slowly - something around 1200fpm. I've tried descending on V?S mode just to see what happens and if I select 2300 fpm I keep accelerating even with the speedbrakes deployed. These conditions are true for the flight depicted above. Haven't tried it with lighter load settings but I woulnd't say my aircraft is too heavy at all: about 65,500 Kg GTOW.Please help!!!If anyone is still interested in the proposition mentioned in the previuos post mail me at victorlima.md@terra.com.br and I'll hook you up with the necessary files/charts.All the best, Victorhttp://www.precisionmanuals.com/images/forum/800driver.jpg


Cheers,
Victor M. Lima
 

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Guest glenb

Victor,I flew the route at fl 290 without SID or STAR. The TOG AND TOD were very close (about 1 min) at the weight and temp of my flight.I let the FMC control the flight via UW62, climb at ECON, to fl 290, till NOA at 4000. The decent was smooth with some drag required.Are you sure the airlines cruise at fl290?Maybe it's the soft warm air you have there. :-)

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Victor,Some points to think about here. -It is a well known fact that the NG is bad at decelerating and descending at the same time.- Depending on the direction and speed of winds aloft you can expect the ToC, ToD and your descent profile to vary greatly. - What was the weather and the pax/cargo load on those flights where you flew jump-seat? That information is pretty much crucial for you to be able to set up a similar flight. Especially if the tolerances are small.Also remember that there is a bug regarding ALT CONSTRAINTS that might leave VNAV in a shallow dive (500 fpm?) after passing a WPT with and ALT CONSTRAINT. The work-around is to recycle the VNAV button.Hope it helps,


Mats Johansson
PMDG Flight Test Dept
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>Victor,>>I flew the route at fl 290 without SID or STAR. The TOG AND>TOD were very close (about 1 min) at the weight and temp of my>flight.About the same for me! what CI did you use Glenn?>I let the FMC control the flight via UW62, climb at ECON, to>fl 290, till NOA at 4000. The decent was smooth with some>drag required.The actual STAR calls for NOA to be at 4500' so you acually did much better than I did (using drag all the way down I got there at about 7000'>Are you sure the airlines cruise at fl290?>>Maybe it's the soft warm air you have there. :-)Pretty sure, says so in the filed flightplan! BTW if you're interested in any or all of Brazilian domestic flights there's a website that's updated monthly and lists all the real flighplans for that coming month for Brazil's most importante carriers ( and two of them work with the NGs) you could go there and I'll help with the translation or give me a coupl of days and I'll arrange them all in a txt file and send 'em to you. Thanks for the help Glenn, I'll try it again tonighthttp://www.precisionmanuals.com/images/forum/800driver.jpg


Cheers,
Victor M. Lima
 

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Once again thanks for the help Mats, I didn't know about that bug and now I thjink that'll help me greatly. Regarding the actual figures, I don't have the actual ones anymore, but I'm 99% sure that taking off with the ZFW very close to the maximum allowed is pretty much a routine operation. The winds are also 99% of the time helping the aircarft along with at least 20+ knots tailwind. And this flightplan was filed as a repetitive flightplan for the month of feb. so I expect that unless some greater weather anomaly was present, they would fly FL290 most of the times. Once again I greatly apreciate th help. Now just a question, does the aircraft weight make a lot of difference with descent and descelleration rates?Cheers,Victorhttp://www.precisionmanuals.com/images/forum/800driver.jpg


Cheers,
Victor M. Lima
 

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Guest glenb

Victor,It seems there are two problems1. You cannot reach cruise alt ToC before reaching ToD.Several factors could cause that.Wind, temp, weight, time it takes to get to stabilized climb and I am sure others.I wonder what airspeed the pilot used while you observed? Using MAX ANGLE climb will get you there in less distance. I used that and it helped.2. The descent is not on the VREF. Too high or too low. A lot of people have a problem with this and found workarounds. After many, many hours of trial and error I am starting to think there may be a problem with the way the FMC approaches a fix with an alt constraint. I have noticed that if in the log page the alt constraints are shown as ___/5000A with the "A" at the end it means at or above this alt. That shows up in most approaches. It is correct to have the constraint "at or above" in some cases but I don't think the FMC handles it correctly.What I do is check all points in the log page and if any have "A" after the alt I edit it so it will look like 170/5000. I also hard enter the desired speed.I hope this helps.GlenI use 111 for cost. It is easy to enter.

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Guest glenb

Victor,I have made several flights you describe.Takeoff Rwy 27R from SBGR using NEMO 27 (I had problems with the restrictions of this SID).UW62SBGL SULI STAR PERES TRANSITIONLand ILS 15C1I had the same problems. Did the pilot use the FMC for the entire flight?Very interesting! Compare an actual flight to the PMDG 737NG simulator.

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Guest jase439

This was very helpful. I couldn't for the life of me figure out why I was in such a shallow descent with the path deviation marker dropping away from me. Thanks.

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