Hi all,Actually I opened almost the same topic months ago but I couldn't get answer that would be help for the problem.Problem is;While descening, speed breaks doesn't support slowing down the plane neither "flight detend" nor "full open" position. Generally I'm calculating descent rate by 1800fpm but sometimes ATC gives new orders that I must be cross at any point or expedite descent (in VATSIM). Even I keep 1800fpm vertical speed (thrust in iddle) plane doesn't slowing down to 250IAS or below. When I open speed breaks, there is no effect on speed. I checked the speed breaks , are they open or not in physically by spot view,they are works as well.(deploy position). If I put gears down, plane slowing down from any speed, so "drag" effect does work by landing gears(honestly it seems too much affect as drag). Is there any chance to change speed brakes "drag" value on aircraft cfg? (I remember there is a value but I don't know what could be possible correct values)Thanks

That's because at higher airpeeds the speed brakes are blown down and will not function with any efficiency.

so, how they could do that in real life when they needed to keep speed with higher vertical speed or slowing down? (I'm really curious, not an argue)Example, we need to slow from 250IAS to 200IAS in 5 nm while descending before crossing IAF point.I always make a plan while descening; below FL260 (when switched from MACH to KIAS) I sets speed 300KIAS until FL200. Below FL200, slows down to 270~280KIAS until FL140, before FL100 I sets all devices for 250KIAS.Plane keeps the speed until FL150 with 1800~2200fpm on iddle thrust,but below FL150 it doesn't. If I set higher value on V/S example 2000fpm on iddle, speed is increasing but with 1800 or below fpm much better, keeps stable the speed but doesn't decrease.I flew several time in cockpit (734,738 and A310)and I saw pilots how used speed breaks when they needed. Also I had a chance that I used real 737NG commercial simulator and we tried to lost altitute in short distance with deep vertical speed+speed breake "flight detend/full" position for keeping speed.It does work as I expected. p.s almost the same problem in PMDG 737NG, she doesn't keep the speed below FL100 more than 1200fpm even you set iddle thrust. When open speed breaksn on flight detend, seems like keeps speed stable but actually not, so you have to open full.As far as I know, speed break flightdetend command does work for keeping speed stable or slowing down in pilot control.I'm not a pilot thatswhy I wrote thats as just only limitted knowledge, I may know wrong :)

I don't fly the 737 and I do not know what the blow-down speed is for the brakes on this aircraft, but I suspect it is around 250+/- KIAS. It may be higher. Read your manual.Above 270 KIAS in the 727 the spoiler acuators will stall and spoiler or speed brake extension likely will not occur. In addition, it may not occur simultaneously on all spoilers causing the airplane to roll uncommanded.

I don't fly the 737 and I do not know what the blow-down speed is for the brakes on this aircraft, but I suspect it is around 250+/- KIAS. It may be higher. Read your manual.Above 270 KIAS in the 727 the spoiler acuators will stall and spoiler or speed brake extension likely will not occur. In addition, it may not occur simultaneously on all spoilers causing the airplane to roll uncommanded.

I'll try this by memory...If you pull the power back you will reduce the "thrust" and you will begin to lose airspeed due to "drag". You will need to increase the "pitch" to maintain the same altitude..Increasing the "pitch" further increases the "drag".. If you partialy deploy the "spoilers" you will decrease the "lift" on the wing and begin to lose altitude.. For spoilers to fully function as speed brakes they need to be fully deployed as when used on landing.. I had spoilers on my Cessna T210...When I would deploy them at altitude I would get about 1200 fpm descent rate and lose about two knots... They did not function as "Speed Brakes" I have about 4 hours in a 737-200 simulator...I remember getting my air speed too high..below 10K and throttled back and deployed the speed brakes...They functioned OK and my instructor didn't challange what I did... Flying is always a balance of Thrust, Drag, Lift and Gravity...You need to plan ahead to be at the right altitude and speed...Ray Lunning

737 has poor speed brake capability. from the 200 to the 900er.schedule your descent with speeds of M .70/280/250 kias, and keep the ratio of 3:1 - or, 3nm for each 1000ft you need to loosei.e. if your destination is at MSL, and the altitude for procedure is 2000ft @ 10dme of the vor/dme that locates at the airport and you are cruising at fl330:you will need to loose 31000 feet. you will loose that in 93nm from the TOD. you must be at 10 dme, add 10 nm to the distance to your destination. so, 103dme from the station, start to descent.if you need to slow down, put 3nm for each 5 knots you need to loose in level flight and idle.

Thanks for reply guys. I already apply 3:1 procedure in my all flights (and in all A/C types even I use FMC/MCDU). As your suggests, it would be much better descent a bit early to earn time and distance for making level flight with iddle thrust. Adding 3nm for each 5 knts is good hint for making calculation, I get noticed.Thanks.