Now that I have spent a little over 10 hours in the PMDG 737, I have two issues to bring up. (1) The T/D seems to be too close to the target waypoint, meaning that all of my decents have to be at a faster vertical airspeed, which means that to keep it at the assigned airspeed, I must...(2) Use the speed brake, which not only is WAY too loud, but seems to have little effect at all on slowing the aircraft down when making a -1800 fpm decent. Also, am I correct in understanding that the flight manual calls for 10 kts above the REF speed on approach?Any ideas? thanks,

Yeah, VNAV PATH NEVER keeps the speed. Does that help you out? Speedbrakes on the NG are just like that, they do not help out very much! I'm sure there are more than a few post by me on this forum dealing with this very thing ;-) And it's +5 on approach..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 there,> Now that I have spent a little over 10 hours in the PMDG 737,> I have two issues to bring up. :-)> (1) The T/D seems to be too close to the target waypoint,> meaning that all of my decents have to be at a faster vertical> airspeed, This is all about planning Captain. The FMC won't do the general descent planning for you. It's a tool for you. Not the all-knowing wizard we all would like to see! ;-)The FMC provides you with a descent profile based on the waypoints, winds, restrictions and procedures you load it with. It's your responsibility to check whether the descent is good enough for you and if it's not, take appropriate action.> (2) Use the speed brake, which not only is WAY too loud, but> seems to have little effect at all on slowing the aircraft> down when making a -1800 fpm decent. Once in a while even if you done your planning oh so meticulously, weather changes or ATC mood swings will throw us off our carefully planned descent. We have several options at hand. And they are all used differently.Speed brakes are used and they are not very effective. This is a pretty slippery baby and once below 10,000 you will have a hard time sinking and loosing speed at the same time. Above 10,000 you can let the speed build up if the conditions permit it. VNAV won't diconnect until a couple of knots from the Mmo/Vmo (Red barber pole area).> Also, am I correct in understanding that the flight manual> calls for 10 kts above the REF speed on approach?I think for an A/T approach the call is Vref+5 at THR and Vref at touchdown. For manual speed management during landing I recall Vref + half the steady wind + the whole gusting wind i.e. if your Vref is 139kts and you have winds at 6kts gusting to 10kts you would try to keep 139+6/2+10 = 152 kts. But I could be wrong here. (Do a search it has been mentioned here before.) Maximum wind correction, I think, is 20 kts. On approach I would expect speed management according to flaps and configuration. A lot of airports have restrictions. ESSA (Arlanda, Stockholm in Sweden) for example calls for maximum 205KIAS withing 20nm and minimum 160KIAS until the OM. Study the chartsHope it helps,

Hey, You cannot descend and decrease speed at the same time, As was previously mentioned, this is a very efficient aircraft, very hard to slow down. You either slow down then descend, or descend, then slow down. This a large aircraft, has a large mass and as such wants to keep moving! If you are still going to fast, then your going to have to take a more shallow descent path, or level out and slow down, then continue the descent. Matthew Murray,[bR]British Airways Maintainence Glasgow.

Slightly off-topic:On a 757 (which is even more slippery than the NG) sometimes it helps (to be used well below 10k) to slow down the bird to below FLAP1 limit speed, and take out FLAP1. This will give more drag, but initially it will decrease the descent rate momentarily.And yes, the FMC is not the all-knowing wizard. Care must be taken and the brain used to arrive at the correct location at correct speed / altitude. You'll learn to adopt FL CH and/or more wiser VNAV management through practise.Have fun!Tero

LOLI've been following this forum for a few weeks now (ever since I bought the 737NG) and almost daily there is a question about VNAV and speedbrakes! :) The funny thing is most people (including me for a while...!) seem to think PMDG made a mistake somewhere... Well, let me all assure you: maybe PMDG even did their job TOO darn well: they even simulated the not so perfect aspects of the NG! Just read (for instance!) this topic on a forum populated by REAL LIFE professional pilots:http://www.pprune.org/forums/showthread.ph...&threadid=50970It's just as if the are talking about the PMDG 737NG! It's as if I'm reading a topic on THIS forum! Let there be no doubt about it: the PMDG 737NG is the best FS add-on there is!

Jeroen, what an excellent little piece of information, thanks for sharing. Indeed, this is exactly how the PMDG 737NG acts. It's incredible to think PMDG have gone as far as to model this little - real world annoying habit - into their bird. Truly outstanding....I can't even imagine how good the Queen's going to be! Best RegardsBoone,[email protected]"Flying a plane is no different from riding a bicycle. It's just a lot harder to put baseball cards in the spokes."

Having spent over 20 years flying 737 and 757/767 for British Airways I feel qualified to say FMC descents hardly ever work out. I and my colleagues rarely used them (except when being checked). If you must, make sure you have the most accurate winds you can get fed into the FMC.The best descents are made using Level Change. A good speed is about 280 as this allows you plenty of room to increase your speed up to nearly MMO/VMO and increase the rate of descent if you start to go above your descent profile. Speed brakes are the last thing to use as they are uncomfortable for the passengers (noisy and vibration) The 737/757/767 are very clean and efficient. You cannot descend and slow up together efficiently. Keep your speed up and then level off at the end of the descent. If ATC asks for a speed reduction dial the speed back to that demanded and if necessary use vertical speed to give a min rate of descent until approaching the requested speed. You must always try to be ahead of the aircraft with your planning and anticipate what might happen. Real airline pilots have a big advantage in that familiarity with their routes means that they know what ATC will ask for. I always reckoned that a trip to an unfamiliar airport added about 30% to my workload on arrival and departure.Happy flyingChris Yates (Retired Captain)

Thanks for sharing Captain Yates. Was the FMC UXXX under 10.4-10.5 on your 737? One of the NG pilots on our team (WestJet) has said that the newest UXXX really is much better in descent than it's predecessors and now they indeed will use the FMC where they would not previously as you mentioned for descents.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 |

The most common error which causes VNAV to be poor in the descent planning stakes is not giving the magic box an accurate wind. If you put no wind in the PERF INIT page and then neglect to add any wind data in the legs page then VNAV will only work out the descent according to a zero wind profile! so if you have a tailwind then you are gonna be High! QED - garbage in = garbage out! I grant you I only fly the classic which is the old wing not the shiny new NG one but we have few problems with VNAV holding the profile. Most problems arise from poor programming of the FMC as above or the operator being less clued up on how the VNAV mode works than perhaps they should be. I don't mean to make this sound condescending but this is often the case and I have done it myself. The simple way to remember how VNAV works is as below:VNAV SPEED - can only do 2 things 1) close the thrust levers and 2) pitch for the target speed shown in the descent page. VNAV PATH - can do only 2 things1) close the thrust levers and2) pitch to maintain the VNAV profile (note this ignores the target speed!!)SO as you might expect VNAV SPEED is about as much use as an inflatable dart board and VNAV PATH is the preferred method of descent. VNAV PATH will do its damnedest to maintain that profile and will literally take you to the barbers pole given the chance (although it will not go beyond it in theory). The FMC will of course tell you VNAV is exceeding the target speed and give the messgae 'DRAG REQUIRED'. This is your cue to do something if you are way off the profile cos it will only get worse.Speed brakes are usefull when in both VNAV modes but only in certain circumstances. They aren't miracle workers and if you only have 10,000ft to go and are 5000ft high on the profile the only thing that will save you is getting more miles with which to loose the height. Speed brakes on the classic work well above 230kt but are pretty poor below 230, thats when you need to operate the 'low speed speed brakes' alternatively referred to as the gear! If you are way high and don't have the luxury of a high speed descent in LVL CHG mode then we often drop the gear. This provides a large ammount of drag and allows you to descend quickly. VNAV is a tricky mode to master and it takes some thinking about but many are fooled into thinking that VNAV is the only mode you can use, LVL CHG is very usefull if you need to loose height quickly, consider this scenarioyou are at 10,000ft slowed to 250kt as is the unspoken law and only have 40 miles to loose the height. VNAV will probably have you about 3000ft high on its profile well here is your get out. Ask ATC for free speed (ie 250kt or higher in the descent past 10,000ft) now hit LVL CHG, wind the speed up to 320kt and delpoy the spoilers, initially you'll be getting 4-6000fpm rate of descent then as the speed reaches 320 it will drop to about 2500fpm. The final part of the method is to keep an eye on the Flight mode annuciator, as soon as it goes to ALT ACQ the throttles will come up so now is the time to wind the speed back to 210kt and keep the speed brakes out. As you level the speed will wash off quickly and the thrust levers will remain at idle thus ensuring no extra energy is added to the situation. 8 out of 10 times this method will get you out of the hot and high situation. Learning this aircraft and its modes takes time and practice, thanks to the fact that this is a sim, you can play all you like so do so, find a method that works for you and never be afraid to ask for more miles. The gate we use at work is that if you are at 4000ft with 20 miles to go and decellerating through 300kt then you are in with a chance of pulling the approach off without to many problems.As always I expect this post will create more questions than it answers but I'm always happy to furnish answers where possible so ask away!RegardsKris Heslop

OMG, this forum is the greatest!! I just wanted to say thank you to the real-world pilots that share their wisdom and experience so patiently with us.

I have to echo what Capt Yates said about descents and speed-brakes.One of the things the real world is very careful of is trying to be efficient because that is where we save/make money....so planning the best efficient decent is very important.We do not operate the 737 (in any form) but I think the FMCs will move the TOD based on the CI index select as well. Next time I get near a TOD I will have to see if that is true.When we first brought the 757 on-line we had all sorts of issues in making crossing restrictions since in the 727 we figured about 5 miles to "Slow at 10" where the 757 took about 12 miles or greater without the boards.Never arrive with the plane at a point where mentally you haven't been 10 minutes earlier....Tim_757

Tero,Yes. On topic indeed. This is exactly what VNAV (in this and any aircraft) is programmed to do as well. General remarks for all (in addition to Kris' and Chris' very valuable input) : (a) A jet aircraft once in descent must retain a rate of at least 1000 fpm (or so the ATC expects). There are only two addons that I know of that do this properly (guess which !). Also, under normal conditions in RVSM areas you must approach you target altitude (whether final or intermediate and whether in climb or descend) at no more than a 1000 feet per minute when within 1000 feet of the target (that usuualy means using VS/SPEED as the active modes for the final part of climb/descend).(:( VNAV will preferentially try to decelerate an aircraft pior to a waypoint with both a hard speed and altitude restriction. This I suppose is what causes havoc (and VNAV discos) for a lot of people in cases of sequential waypoints associated with large speed AND altitude differences. Remember the CDU will accept anything... However, when the time comes for that leg to become active and sequence the waypoint (or the DECEL marker) whether the aircraft can actually handle this or not, it is something you the pilot-in-command must decide and facilitate if possible. To add emphasis to what Tero said : Decision making is the major, challenging and rewarding part of what pilot-in-command means, not a guy pressing buttons to startup systems at the gate...© The speedbrake effectiveness is very accurate. Regrettably almost every other add on I have seen (plus MS default planes) have it calibrated so impossibly wrong and people got used to this.TIP : Based of Boeing performance charts you'll need (at 10000 feet) about 0.2 miles per IAS (knot) reduction in the -800, 0.15 for the 800WL/700WL and about 0.1 for the 600/700 (no winglets). Yeap that's correct the -800WL is slightly less slippery in descent that the 800 without winglets (initially thought Boeing had typos in the performance charts !) Best,Vangelis===================================== E. M. Vaos Precision Manuals Development Group www.precisionmanuals.com=====================================

Good info, Van !As a further tip to interested people: get yourself a copy of the Bill Bulfer FMC guide, there are different editions for it for the 737 and others (the Big Boeing FMC guide handles 747/757/767/777). I highly recommend reading it, as it will give a very broad perspective on FMC ops.bw,Tero