drag required and some other things

[Guest patten]

1)what I quite don't understand is that many often I get a message from the FMC that drag is required from as high as above 20000 ft.Is this common ?2)most of the times I get VNAV disconnect and end up to high to capture ILS.I thougt that the FMC would calculate the apropriate descend profile to get things right?right?3)when downwind and turning base -final (with LNAV) most always ,the plane makes some kind of a shortcut and never flies above the fix(es), so again ...to high...this happens using the SIDS&STARS as provided.I don't know , but I have the impression that it,s wurse since the service update (might be subjective, though)hope that someone can help,Patten

[dfish 1]

I'm having the same problem. I insert the STAR before descent and always loose the VNAV sometime during approach. I've setup the wind on the forcast page and I'm not overspeeding. Then when I revert to LVLCH I always endup high on the GS.Dave FisherCYYZP4 2.8 GB 478P 533 MHZ CPUP4P800S Asus Motherboard512 DDRGeforce Ti 4200/128Maxtor 80 Gig ATA 133 HDhttp://www.precisionmanuals.com/images/forum/ng_driver.jpg

[Guest Nickman]

All those problems can be from not entering the decent wings. Enter the destination's wings into the DES FORECAST page. Since you can only enter 3 layers, make on every 10,000 feet or soNick B.Continental Airlines Virtual 737NG Pilothttp://www.precisionmanuals.com/images/forum/800driver.jpg--AMD Athlon XP 3200+ @ 2.2 Ghz (Equal to 2.8 ghz)400W Power supply3x 80 mm Case FansSoyo VIA KT600 Dragon PlusnVidia GeForce FX 5200 128 mb2 x 512 PC400100 GB Western DigitalMicrosoft Sidewinder Precision 2

[Guest speight]

It seems to help if you go to the descent page and click "Desc Now" at 20nm before the calculated TOD. If "Drag Req" comes up, then deploy spoilers. This way, the profile is retained, though it does seem a bit unusual.

[Guest patten]

the problem is : although the descend path seems to be flown correctly, that at some point (say about 6000 ft or less) VNAV disconects,without warning. By no way (but a very uncomfortable for passengers)you can correct it (steep descend).So it's too late to anticipate.In adverse , you never get too low, always too high, wathever the winddirection.So , in real , with a sophisticated FMC , could this happen, or is this PMDG "virtual FMC" not as real, or is it something else ?Patten

[Guest Erups]

Adding my experience to this discussion:the fact that spoilers are called for too often is true, or at least is true for me.It happens very many times.Then i too have to point a finger at the vertical path following precision of the FMC.It is not that precise as advertised.It becomes all the more un-precise if you setup precise altitude and speed constraints.I mean that if you plan a route and do not enter any manual speed or altitude constraint for any point, the vertical path is unprecise but acceptable.If you ever happen to enter any constraint, say adios to your vnav path.It goes nowhere near where you expect it to be.For example, i often land at Rome Ciampino (LIRA), the ILS passes over Urbe civilian airport (LIRU) and before that there are minimum altitude constraints due to hills and radar.So if you plan it the way it is intended to be flown, you have very many constraints:CMP 6000ftURB 200/3000 which means you HAVE TO BE at 3000 at URB because it is the ILS intercept point.Whenever i use such a setup, manually entering the contraints, the plane always fails to fly such a path: a DECEL point is created, and the plane refuses to maintain the necessary vertical speed prior to that point; when it reaches that point, it further levels up to reduce speed then dives in, but the vertical path has already gone to hell long before and you end up well above the glideslope and all the more above the altitude you should have been.

[Guest Nickman]

You must not be setting up the FMC right. Keep in mind that the FMC is designed to help you, not do it for you. You have to use your skills to determine to use spoilers (even if you get no message), descent faster, etc.You should also make sure you enter a descent target speed speed about 10 kts below your cruising KIAS (ex: if you cruise at FL350 and your cruising speed is 280 KIAS, make your descent target speed about 270 KIAS). The reason I say this is because the default descent speed is 315, which at FL350 is almost 600 kts and way to fast and can cause overspeed disconnect.Nick B.Continental Airlines Virtual 737NG Pilothttp://www.precisionmanuals.com/images/forum/800driver.jpg--AMD Athlon XP 3200+ @ 2.2 Ghz (Equal to 2.8 ghz)400W Power supply3x 80 mm Case FansSoyo VIA KT600 Dragon PlusnVidia GeForce FX 5200 128 mb2 x 512 PC400100 GB Western DigitalMicrosoft Sidewinder Precision 2

[Guest patten]

Your example is just what I wanted to say, you 're quite right...so after all, the PMDG FMC does not what it should do; does it ?Could someone of the PMDG team answer this ?

[Guest patten]

Nick, I think you're right if you have to use your skills, and it works (most of the times); but what's the point then having such a sophisticated system, if you can't realy relie on it ?

[jacsantos 0]

Yes it does happen to me too, if I let it. ONE problems bugs me in the fmc though: whenever VNAV is disconected,at X nm from a waypoint or an airport, an I fly the rest of the flight in basic autopilot ( hdg, vs, spd..) the distance to airport or whatever in the progess page of the FMC increases as the flight progesses in the right direction. So it's useless to aid calculating the 3:1 rule of the descent, since it doesn't provide acurate distance to waypoints/airport.

[crvm 0]

To the orginal poster, you are required to sign your real name while posting on this forum, please take a moment and read the rules here, thank you. http://forums.avsim.net/dcboard.php?az=show_topic&forum=136&topic_id=2402&mesg_id=2402&page= I think a very important issue is missing from this conversation, namely, that the default VNAV does not keep speed just like the real bird. Descent is not set it and forget it. We as the PIC must monitor and plan our descent, this is one of the greatest challenges to flying this type of aircraft. Let me answer some questions from the orginal post."1)what I quite don't understand is that many often I get a message from the FMC that drag is required from as high as above 20000 ft.Is this common ?" Anytime you are 10 knots or more over target you will receive this message, it does not matter what altitude you are at. It is the pilot's responsibility to control the aircraft speed, the AFDS will not make any attempt to keep the target when in VNAV PATH. If you become too slow the FMS will add some thrust."2)most of the times I get VNAV disconnect and end up to high to capture ILS.I thougt that the FMC would calculate the apropriate descend profile to get things right?right?" You actually have two questions here so will answer both. First, you will only get a VNAV disconnect ifa: Are not controlling speed which has reached 15 knots over the target which happens to be 240 knts under 10000', over 10000' you can reach the barber poll before reversion to another pitch mode.b: You have some constraint that is out of the ability of the FMS achieve.You have a speed constraint without having an altitude constraint on the same wpt. You have a discontinuity. c: You have touched the controls with the A/P engaged causing reversion to another pitch mode such as LVL CH or CWS P. Second, the FMC calculates a proper descent profile based upon what you have entered. You have a VNAV path deviation scale on the navigation display to monitor your profile. I have followed this in V/S on the dime to the RWY. "3)when downwind and turning base -final (with LNAV) most always ,the plane makes some kind of a shortcut and never flies above the fix(es), so again ...to high...this happens using the SIDS&STARS as provided." You are confusing what is displayed on the ND and how the 737 actually follows such tight turning paths. I will state this with some backing from others who know the NG in and out that this is a very complex add-on and it takes some time to master flying correctly, what it boils down to is the PIC's technique. I know Mr. Brad Marsh has talked about this very issue we are discussing and has said some of the same things. He takes folks on a flight that he published in his Geezer Guide and does not suffer from what we see here. This is because he knows exactly what to expect and how to handle the situation and plan ahead. I cannot stress enough the importance of taking some time learning the systems on this aircraft and what to expect. Best Wishes,[h4]Randy J. Smith[/h4][h3]P M D G's 747-400[/h3][h4]coming to a runway near you[/h4][/font color]Caution! Not a real pilot, but do play one on TV ;-)AMD 64 3200+ | ASUS KV8 DELUXE | GFORCE 5700 ULTRA @535/1000 | Maxtor 6Y080M0 SATA 80 GIG | 512 DDR 400 | Windows Xp Pro | Windows Xp Pro 64 |

[chumley 0]

I have frequently flown in real life in a 738 and I cannot recall a single flight where spoilers were not used at some point during descent.Spoilers are made for a very specific job and they do it very well both during descent to slow the slippery sucker down and upon landing to kill lift.Imagine aircraft from the Kangeroo airline (Qantas) without spoilers - they would imitate the image on the tail and Boeing would have to rebadge themselves dropping the 'e' from their name 'Boing'. :D Andy b

[Guest Nickman]

The PMDG created the FMC as close to the real thing as possible. You must remember the FMC is there to help you, not do the work for you. If it was to do the work for you, you wouldn't even be on the plane, just the FMC and passengers. It's your discretion on when not to rely on the FMC.Nick B.Continental Airlines Virtual 737NG Pilothttp://www.precisionmanuals.com/images/forum/800driver.jpg--AMD Athlon XP 3200+ @ 2.2 Ghz (Equal to 2.8 ghz)400W Power supply3x 80 mm Case FansSoyo VIA KT600 Dragon PlusnVidia GeForce FX 5200 128 mb2 x 512 PC400100 GB Western DigitalMicrosoft Sidewinder Precision 2

[dfish 1]

I use FSNAV for flightplanning and sometimes I'll use a STAR from their database. I wonder if their descent paths are unachievable?BTW, where can I find Brad Marsh's "Geezer Guide", I've searched the library but no luck.Dave FisherCYYZP4 2.8 GB 478P 533 MHZ CPUP4P800S Asus Motherboard512 DDRGeforce Ti 4200/128Maxtor 80 Gig ATA 133 HDhttp://www.precisionmanuals.com/images/forum/ng_driver.jpg

[crvm 0]

It was removed from it's sticky position, well here is a link to Brad's home page http://homepage.powerup.com.au/~speedyBest Wishes,[h4]Randy J. Smith[/h4][h3]P M D G's 747-400[/h3][h4]coming to a runway near you[/h4][/font color]Caution! Not a real pilot, but do play one on TV ;-)AMD 64 3200+ | ASUS KV8 DELUXE | GFORCE 5700 ULTRA @535/1000 | Maxtor 6Y080M0 SATA 80 GIG | 512 DDR 400 | Windows Xp Pro | Windows Xp Pro 64 |