SimmersI have been flying the PMDG 737's for some time now but always encounter one problem during descent.I start the descent as usual in VNAV mode the aircraft tips over and starts its descent but it always sacrifices speed or path. if i keep its speed on track it has to raise the nose to slow down. Thus losing its descent path. to get back on descnet path it tips down at a steeper angle to catch it again but the result of this is that the speed goes way over. sometimes even with the speed brakes.If i keep the aircraft on its descent path and disregard speed then by the time it comes to speed restrictions or even in some cases landing the aircraft is very fast, over 250 knots under FL100 in some cases.Using LVL CHG also does something similar to get the aircraft to slow down it raises the nose thus losing descent path.Does anyone have any tips i could use to get the aircraft on a managable speed/descent. I have tryed starting the descent earlier but i would prefer if i would not have to.Thanks in Advance

Hello, you will need to sign your name on this forum, thank you sir. but it always sacrifices speed or path That is correct. VNAV PATH is not concerned with SPEED but with keeping only the path profile. The FMC makes predictions based in part by the input in the FORECASTS PAGE which the pilot programs. The target speed is for refernce purposes only. You can select VNAV SPEED prior or during DEScent from the DES PAGE which will keep the target speed and sacrifice the path. As you are able to see, descent is the most difficult phase of automated flight. One must be ahead of the aircraft at all times. Also, we cannot have it both ways in VNAV, it's either path or speed. Now as you already noticed, one can *control* to a certain extent, the speed in VNAV PATH by use of the speed brakes or by increasing throttles by holding down the F4 button while in descent. In this way, if you are either too fast or too slow, you can *help* the aircraft stay closer to target. This is very important when you are nearing the airport restriction altitude (240/1000) where you do not have as much leeway in excess speed before AFDS reversion to another mode (kicks out of VNAV). Best Wishes,[h4]Randy J. Smith[/h4]http://www.rawbw.com/~bdoolin/shinault/Animation1.gifCaution! 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 |

Randy,* The FMC makes predictions based in part by the input in the FORECASTS PAGE which the pilot programs. The target speed is for refernce purposes only.*If i input a Headwind into the FMC forecasts page is the PMDG modeled to start a descnet ealier or make speed adjustments for that?Daniel

>If i input a Headwind into the FMC forecasts page is the PMDG>modeled to start a descnet ealierTheoretically, in order to obtain an early descent you should use tailwind, not headwind.But i dunno if it works.

Daniel,If you input a headwind then the FMC will start the descent ** later ** not earlier, since for the same target IAS, ergo same target true airspeed, your ground speed will be less. If you are interested in getting the plane down with a margin to spare try an ISA deviation and tailwind in the forecast page, higher than what you get from your weather programme. The programmed relations are non-linear but approximately 2 deg isa or equivalently 10 knots tail will result in the plane starting descent about one mile plus earlier.(Yes the entries in the forecast page are all used and connected to math...not there for fun/show. If you have no forecast VNAV PATH is useless). Finally, remember all the NG's do not have the same descent performance. The worse of them all is the -800 (no winglets). Hence, the fact that you mastered the -700 (best performer) does not mean that the same performance is to be expected from the 800 or the 900 or the 600. Each model is tuned and treated as a completely different aircraft to manufacturer spec/data.Best,VangelisPS. And...as Randy said VNAV path will make no effort to keep the speed up to target. It depends on how good is the forecast input and how abrupt the wind change is going to be given MSFS shortcomings in this area. Monitor speed and bleep the throttle (use F3,F4) or use the speedbrake momentarily. Note that in the real world (even after FSUIPC v3.30) wind changes are never ever that abrupt as in FS9 unless you hit a patch of moderate to severe turbulence.===================================== E. M. Vaos Precision Manuals Development Group www.precisionmanuals.com=====================================

Ok,can i please ask what ISA is? Sorry but im not hat advanced! :)Daniel

The 737 NG seems to be a low drag aircraft, which is a good thing at cruise, but results in challenges during quick descents like KSAN. It also has a high angle of attack on optimal final (5 to 6 deg).When in VNAV PATH, watch your airspeed like a hawk, and if it starts nudging up, immediately use the speed brakes. A little more elegantly you would cancel the descent and level off to slow down, but if you don't have much leeway in the profile, then you can't do that. If you get more than 15 knots above (or below - that is rare) then VNAV will kick out, you should never let it get that far out.In VNAV SPD the FMC does the speed watching, but then you can lose the path. You need to use the speed brakes (rarely a little extra thrust) to maintain the path then.As already mentioned putting in the winds aloft forecast, especially for tail winds, will help.* Orest-~~~~~~~~~Orest SkrypuchUAL1445 DENFOCYFD - Canada

If you get more than 15 knots above (or below - that is rare) then VNAV will kick out, you should never let it get that far out. This is only true BELOW the airport restriction (240/10000), as above this one can reach MMO/VMO (barber poll) before AFDS reversion but VNAV will stay engaged well beyond 15 knots.Best Wishes,[h4]Randy J. Smith[/h4]http://www.rawbw.com/~bdoolin/shinault/Animation1.gifCaution! 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 |

Hi Daniel,ISA stands for International Standard Atmosphere, a theoretical model of the atmosphere that states for each altitude the "standard" values of many variables, including temperature and pressure. At sea level, the ISA says that the standard values are +15