Hello,do you know why I found very difficult to perform a correct speed descend (250 KIAS) without using speedbrake even if the rate of descend is not so high (about 1500-2000 Ft/min)? I think that the effect of the speedbrake is too low. It practically doesn't reduce speed at all.

Yep the speedbrake mimics the real one very well, it does nOT help that much on the NG as stated by the NG pilots on the team. As for you speed issues, well that is realistic too. One should not expect to SLOW and DESCEND well at the same time on the NG. Even in VNAV in PATH mode you have to control the excess speed. So what we *think* and what *is* are two very different things...Best Wishes,[h4]Randy J. Smith[/h4]http://www.rawbw.com/~bdoolin/shinault/southparkcartmad.gif[h3]PMDG 747![/h3]Caution! Not a real pilot, but do play one on TV ;-)ASUS KV8 DLX | AMD 3200 64 | 1 GIG PC 3200 DDR | GIGABYTE 5700 ULTRA | ViewSonic VP192b 19" |

HiYou will find in the FMC there is an option to perform a econ decent and decelertate before the descent begins.Also above 10,000ft there is no need to slow to below 250kts. if you find that you are gaining too much speed, descend to 10500, reduce throttle to idle and set the speed to about 240, then begin decending again, you will find that the speed brakes will have more effect. Also try reducing to flap 1/2 speed, this will help maintain a slower descent.:) paul

I also have a lot of trouble controlling my speed in descent,so what's the secret of descending then please ? - spoilers up, flaps out as well (should you do that as a means of slowing down ?) otherwise how else do you slow the darn thing down and get to the correct height without getting a 'Descent Path Unacheivable' message ??On odd occasions flying from EGLL - EGPF with a Lanak1B arrival for ILS r/w 23 (DCS transition), I have succeded in getting down at the right place and at the right speed but not really sure how I did it and it doesn't necessarily work the same the next time. Is it better to insert some early speed contraints or not ? and yes I have put some wind into the FMC - 250 at 10 knots typically) OAT 8 degrees C.Could someone explain how its done in rl please ?(737-600/700 with FS 2002)

I would second what paul just said. Particularly with the level off before 10,000. The key thing to remember with the speed brakes on the NG is that they are abit like the continuos (sp?) braking systems fitted to modern road busses/coaches, in that they don't actually slow you down, but they help considerably in holding a set speed; thus you must extend the speed "brakes" at the begining of your decent if you anticipate a problem with any speed constraints, not at the point when your at or over the speed limit. this should provide you with a good rate of decent and some degree of speed control. Additionally, excercise goopd planning and judgement before you decend, make sure that the decent targets presented to you are realistic, and if they are not then ammend them way before you plan to decend. Doing this sort of planning in the cruise is good practice and a great way to cure boredom. Jamie Whiting, England

>I would second what paul just said. Particularly with the>level off before 10,000. The key thing to remember with the>speed brakes on the NG is that they are abit like the>continuos (sp?) braking systems fitted to modern road>busses/coaches, in that they don't actually slow you down, but>they help considerably in holding a set speed; thus you must>extend the speed "brakes" at the begining of your decent if>you anticipate a problem with any speed constraints, not at>the point when your at or over the speed limit. this should>provide you with a good rate of decent and some degree of>speed control. Additionally, excercise goopd planning and>judgement before you decend, make sure that the decent targets>presented to you are realistic, and if they are not then>ammend them way before you plan to decend. Doing this sort of>planning in the cruise is good practice and a great way to>cure boredom. >>Jamie Whiting, EnglandThey are called JAKE brakes. The Jake brake turns a desiel engine into an air compressor, in essence. A compression brake which acts as a retarder. Saves the heck out of the vehicles braking system/brake shoes, pads.Wont help much if your airborn tho, he,he.Best

Thanks for that, I'd always wondered how those things worked, pity there is not a bus simulator around!!

Hi there:I also had this problem, but solved it by ensuring that I apply the spoilers before final decent whilst flying level at idle thrust, then as my speed retards from 250 to say 210, I then decend on the glideslope (flying manual). It seems to work well for me and I rarely get overspeed issues or issues with too much speed on final decent. May help you also.........Iain

I found that using level change helped a lot. By the time I'm at 10000, I'm at 250.- hn

I found that slowing down to 260-270kias before top of descent gives much better cotrol. This can be accomplished in the fmc.

A few descent keys1] Do not use VNAV with restrictions on the other end, if you do make sure you are not going a zillion knots when you need to slow to 240 under 10, I think you can tell why.2] If you find yourself with MUCH excess speed simply hit ALT HOLD for a minute, this WILL slow you down thence resume.3] Do not listen to those experts who proclaim that speedbrake use is for wusses or bad pilots, put it out when you NEED IT. 4] Do not think that IF you are not useing VNAV that somwhow using other modes like V/S or LVL CH are *not realistic*, they are used in rl too so when things start to look dark try all availible options at you disposal. V/S with the green arc is partically fun ;-)5] If you are VNAV king then do not make a route full with physics bending restrictions. If ATC does not call for restrictions do not put any that are not needed. Try VNAV SPD in these cases, under 10' you can revert back to path or whatever else. Also, place some HEAD or TAILWIND on the FORECASTS PAGE if you have an idea of the wind, be LIBRERAL a bit here, this will help the FMC with the path.6] Number one, VNAV PATH has nothing to do with SPEED, that's for you the PIC to control and monitor so do not wait unti the nose starts pullin at v10' to slow to 240 and you are at the barber poll and then question why it did not slow itself! Best Wishes,[h4]Randy J. Smith[/h4]http://www.rawbw.com/~bdoolin/shinault/southparkcartmad.gif[h3]PMDG 747![/h3]Caution! Not a real pilot, but do play one on TV ;-)ASUS KV8 DLX | AMD 3200 64 | 1 GIG PC 3200 DDR | GIGABYTE 5700 ULTRA | ViewSonic VP192b 19" |

2] If you find yourself with MUCH excess speed simply hit ALT HOLD for a minute, this WILL slow you down thence resume.So basic Randy - ALT hold of cause!....Iain

Whats the difference between VNAV Path and VNAV Speed?

As far as I know (please correct me if I am wrong), in VNAV Speed, the FMS calculates a descent that allows you to descend the plane following a constant and gradual descent rate, maintaining the thrust in idle and the desired speed. The VNAV Path, gives "more importance" (didn't find better terms to describe it) to the altitude contraints, that is, it accomplishes every altitude (hard) contraints, even in a no gradual descend, and doesn't give priority to speed maintaince with thrust idle and a consequent rate of descent that allows you to maintain that same speed. This means that the plane will follow a descent rate calculated by the FMS that allows you to accomplish the contraints, and not the speed maintaince using just thrust idle. This means that sometimes, to maintain the speed, you will need to use the speed brakes, if the speed is increasing, because the aircraft will not slow down the rate of descend to decrease the speed, as it would have happened in VNAV Speed, or, in vice-versa, the auto-throttle system will increase thrust to regain the wanted speed, instead of increasing the rate of descent to regain that speed using the thrust in idle, just as it would have happened in VNAV Speed.Making a very very very very bad comparison, VNAV Speed is like LVL Change, and VNAV Path tries to accomplish your contraints.(bah, sorry for my bad english :()

As far as I know (please correct me if I am wrong), in VNAV Speed, the FMS calculates a descent that allows you to descend the plane following a constant and gradual descent rate, maintaining the thrust in idle and the desired speed. No that is not correct. VNAV SPD does not follow anything at ALL except keeping SPEED. The VNAV Path, gives "more importance" (didn't find better terms to describe it) to the altitude contraints, that is, it accomplishes every altitude (hard) contraints Not correct either, both VNAV modes will honor altitude restrictions just perform it slightly different since SPD is not concerned with PATH it will at times reach a certain altitude prior to a fxed altitude restriction and LEVEL OFF until passing as one example. This means that sometimes, to maintain the speed, you will need to use the speed brakes, if the speed is increasing, because the aircraft will not slow down the rate of descend to decrease the speed, as it would have happened in VNAV Speed, or, in vice-versa, the auto-throttle system will increase thrust to regain the wanted speed, instead of increasing the rate of descent to regain that speed using the thrust in idle, just as it would have happened in VNAV Speed. This would never happen in VNAV SPD since it is speed bound, not path bound.Best Wishes,[h4]Randy J. Smith[/h4]http://www.rawbw.com/~bdoolin/shinault/southparkcartmad.gif[h3]PMDG 747![/h3]Caution! Not a real pilot, but do play one on TV ;-)ASUS KV8 DLX | AMD 3200 64 | 1 GIG PC 3200 DDR | GIGABYTE 5700 ULTRA | ViewSonic VP192b 19" |