Slowing down to 250kts

[Guest Jeroen November]

Hi all,I've noticed, as some others, that slowing the PMDG down to 250kts (or slower) below 10.000ft. isn't a piece of cake. I can understand that slowing a plane isn't as easy as hitting the brakes in a car, but I do have some thoughts.I usually fly a manual decent at about 2000 ft/min, cause VNAV gives me too much of an irregular climb/decent (as excellently put in the advanced tutorials by Timothy Metzinger). But even when I reduce this rate to about 1500 nearing 10.000ft & with the speed brakes on I have a hell of al lot trouble slowing even below 300 KIAS. I suppose (correction I'm sure)the PMDG is modeled close to the real thing, but is it possible that the braking force of the in-flight spoilers is a bit on the down side?Another thing why I'm bothered with this problem is that I've noticed that the FS2004 ATC, when flying IFR, notifies me irregularly when to start my decent. It's like they don't know which runway I'm supposed to land on, whether I have to pass the airport on my decent and return for the runway or do a direct fly-in the ATC orders the start of my decent nearly at the same point. The latter of course implies a much steeper (& faster) decent.Greets,Jeroen

[Guest captain_dirk]

I have the same problem, with a normal descent rate of 1800 feet and speed brakes engaged, it is impossible to reach and maintain 250 knots below 10.000 feet. I wonder of this is a fault of the PMDG 737 design. I also wonder if engaging speed brakes to reach 250 knots is realistic. At least, in the default FS2004 planes, engaging speed brakes to maintain 250 knots at a similar descent rate is not necessary.Dirk

[Balint 18]

Gentlemen,I am sure this is a real issue, I have faced it several times as well. The FMC however needs proper wind information to calculate descent profiles, including T/D, rate and so on. Do you always properly configure the FORECAST sub-page on the DES page regarding winds, QNH and temperature?Cheers,

[crvm 0]

Well you are all right, it's a real issue here and in real life. The speed brakes on a 737 NG are not very helpful and they are modelled they way they are here according to the rl pilots on the beta team input. There are many ways to get the bird to slow correctly but in VNAV it is never just a sit back and watch situation, one must always be aggressive in helping the plane decel and if youy are using a speed other than the ECON this is even more the case since VNAV predictions are based upon the target, so if one keeps the plane close to target in descent slowing at the airport restriction wil be much smoother..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 |

[philbrown 9]

I've noticed that when I've been on a VNAV descent, on passing about 110 the autopilot changes the speed to 240, and the rate of descent falls to 500fpm to allow the plane to slow down.This seems to be included in the planning by the computer of the descent profile, as I'm usually passing 110 with about 10 miles to run to the point at which I need to be level at 100. Gives plenty of time for a very slow descent in order to bring the speed back.Also, I can remember a post by a real 737 driver who said it is not uncommon for speed brakes to be used during some or all of the descent.-Phil

[falcon999 24]

Hitting waypoint target speeds is also about good decent planning. You need to make sure your waypoints are setup to give you plenty of time to decend and slow down. I generally use LVL CHG for decents below 10,000ft. Keeps the speed managed and provides a nice passenger friendly ride. :-)

[Guest bobsk8]

I try and use speed brakes while looking at my distance from the airport, when following ATC instructions, so that by the time I get to 10,000 feet I have already slowed down to about 275. I level off at 10,000 until the speed bleeds off to 245, and then resume the descent. It works everytime.

[Guest Jeroen November]

All,Thanks for the answers...I perfectly understand your answers concerning VNAV etc...but the problem remains that I don't decend until ATC tells me to. So the decent is heavilly ATC-dependant & they decide at what distance from the airport it starts & thus in over 50% of the cases I need to decend at 2500 ft/min or more to cover the altitude difference to arrive at the ILS at the correct altitude. This implies the 250 KIAS under 10.000 ft is next to impossible using PMDG737's in conjunction with standard FS2004 ATC, allso because the FS2004 ATC doesn't care what the final part of your flightplan (STAR) looks like, it just tells another heading to fly & your timed VNAV-planning becomes useless. This is of course perfectly explainable by the difference in realism of the two products...but it remains an irritant fact. What Microsoft should do is implement SID's & STAR's in their ATC so that they can just tell you to fly that peticular one, 'cause now I can imagine a lot of pilots diving to the runway if they have to follow FS2004 ATC-instructions. I can recall one event where the FS2004 ATC tower cleared me to land (airport nearly at sea-level) like there was nothing wrong, I was 7 nm out & at an altitude of 15.000 ft...so if anyones makes a repaint of any of the PMDG's in 'AIR ROLLERCOASTER'-livery, I'm game! :) Greets,Jeroen

[falcon999 24]

Hi Jeroen,"What Microsoft should do is implement SID's & STAR's in their ATC so that they can just tell you to fly that peticular one"Had a thought... are you adding the STAR to your MS Flightplan (including altitude constraints)? I don't us MS ATC much (fly on-line w/Vatsim), but when I have the ATC follows the STAR. If not this would explain MS ATC's behavior.

[Guest tcable]

It's comonn knowledge in the pilot comunity that most modern jets can;t really "slow down and go down" at the same time. sems to drive controllers nuts :) It's one or the other.I usually start my descent in VNAV (if appropriate), but usually end up in a VS descent to the area of 10k, then below that a 240kt FLCH descent. It depends on the situation. SOmetimes You'll get sla dunked and pop the brakes and do a FLCH decent for 30k feet! (Bad on the ears IRL, BTW!)The key is planning. Think ahead. as time goes by, you get used to the distanceds needed to decellerate from 320 to 240 at 10k and can plan accrodingly.I kive next to KTAN and watch the jets into Boston come over between 11-9k. You can hear the changes in thrust settings as they fly over- levelling out or starting the next step in their descent.Tim

[jc_150 3]

Hi allI have read all these posts and agree with them all, so I thought it was time to inject a little humour into a serious subject. I take my flying fairly seriously, and also use Vatsim for my online flights and their ATC. Cannot comment on FS9 ATC as I dont use it, I tried it once and it told me to change runways about 500ft away from my landing, so gave that up.So as i think that it is a noise problem to be at 250 kts below 10000 ft and for a lot of flights if there is no controller, then i am getting away with a little consession if the plane won't slow down to that speed because of my bad planning. However again because of my bad planning a Vatsim controller insisted that i slowed down to the correct speed even though i was decending and autobrakes on, and when i told the controller that I would have to bow to his superior knowledge on how to do this when decending and slowing down at the same time i was told to slow down at my earliest convenience, which is usually accepted by Vatsim controllers using common sense. So there you have it, we have an excellent plane, pilots of all skill levels, ATC with different controlling abilities, with and without a sense of humour. real world rules, our interpretation of them.....all wrapped up in one package which we all love ie fs9. and the experience gets better every time i use it.all have funJohn Callejawoops amended after posting..shows my flying ignorance..said autobrakes when i meant spoilers.

[falcon999 24]

Hi John,Good point! In the R/W the PIC always has the last word. In my experiences, if the PIC states that they are "unable to comply" then the controller will do the following to accommodate; vector other traffic around you, vector you or both. So VATSIM is just simulating what would happen in the R/W. I have found myself in this situation a few times. Although the controller may not have been happy, PIC means that I have the authority to make the final decision concerning compliance to the controller's instructions. More importantly this is how the FAA and the insurance companies view PIC as well! :-)

[Guest Jeroen November]

Good point...I'm glad I brought it up!!!

[Guest ChrisY]

As a real world 737 pilot the modelling seems about right. I have said before on the forum you must remember these aircraft are very clean and the speedbrakes are relatively ineffective. Remember one thing about the 737 (or 757/767) you cant really descend and slow down at the same time. One or the other. If you have to slow down quickly for ATC or a speed limit point you must kill your descent rate to get the speed back then descend again at the new speed if necessary keeping the speedbrake out. If you can avoid speedbrake use it is preferable because it is not good for passenger comfort and surprise surprise they ultimately pay your salary! You normally have a good idea where speed reductions will be required allow for this in your descent planning and add extra miles for the aircraft to slow down (1 to 1.5 miles per 10Kt speed reduction) If all else fails you can always tell ATC they are asking the impossible but not of course if you cocked up the planning in the first place. They know what you can and cant do!Capt Chris Yates

[crvm 0]

.but the problem remains that I don't decend until ATC tells me to. So the decent is heavilly ATC-dependant & they decide at what distance from the airport it starts & thus in over 50% of the cases I need to decend at 2500 ft/min or more to cover the altitude difference to arrive at the ILS at the correct altitude. Simply do not use VNAV ANYTIME you expect ATC to disrupt or many restrictions on descent. If you wait till after passing TOD to descend the plane will DIVE for the path and you will be speeding quite a bit. VNAV loses any meaning in these situations since it is based on predictions no longer valid to your current situation.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+ | NEC LCD 1980SXi 19" | ASUS KV8 DELUXE | GFORCE 5700 ULTRA @535/1000 | Maxtor 6Y080M0 SATA 80 GIG | 512 DDR 400 | Windows Xp Pro |