I have been finding that with a lot of so called FSX addon aircraft that upon passing FL300 there is a big problem with the planes wanting to stall out. I plot my flights carefully checking that I have the needed fuel and a tiny bit extra. Making sure my payload is correct. And in every 737-800, 757-300 flight I have made, once i hit fl300 the airspeed makes a huge slow down. As a result I have to lower my vertical speed too almost 100 each time, and even then I am lucky to hold 180kts. Has anyone had this happen, and if you fixed it or figured out what is causing it, please reply.

Check the wind speed and direction. Maybe its a real heavy headwind your flying in to.What is your climb rate also?. try around 1000 fpm or less. I havent had any problem and have many addon aircraft, payware and freeware.daveo (ESSB)

Yes, pilot error...First, understand that as your altitude increases, decreased air pressure will cause the IAS (Indicated Airspeed) to drop. This is absolutely normal... You simply have to understand the relationship between IAS and TAS (True Airspeed).What is happening is that you are "getting behind the power curve" with regards to airspeed, and quite simply have insufficient power even at full thrust to recover.Once you're at this point, the proper recovery procedure is to switch off the autopilot, lower the nose a bit, and let your airspeed recover.To prevent this, monitor your IAS carefully and never let it drop below stall speed for the aircraft you're flying.For an excellent visual display of the relationship between altitude and IAS, check out this cool on-line simulation:http://www.luizmonteiro.com/Learning_Pitot_Sim.htmUsing your mouse, you can set your "true airspeed" and "change altitude", then observe how as altitude increases, IAS decreases.If the stall speed for the a/c you're flying is say, 170 knots, then allowing the IAS at any altitude to get too close to 170 will "put you behind the power curve."For example, if you set the TAS on this simulator to 220 knots, then increase your altitude to 17,000', notice that your IAS has now dropped to around 170 knots... This is very Dangerous Territory as you are now AT or NEAR stall speed!As it happens, the above conditions are grossly simplified, as you play with the on-line simulator you'll notice that IAS is also affected by ambient temperature, ambient pressure, and even the "Station Reporting Altitude" from which the Kohlsman pressure setting is given (as long as you're below FL180 of course).

Yup, I once read that in a U2 at operational altitude the difference between buffetting and stall was 7 knots. I take my hat off to the pilots flying it for many hours. (Would make an interesting mission for FSX)John

No doubt! That U2 was not the sweetest of rides, but it was still an amazing aircraft. Large airliners (and other jets) can perform a "step climb". I know I have a chart showing this somewhere, but just now I don't know where it is. Wiki also has an entry for "step climb". FSX doesn't like to have you step climb as the FSX ATC will nag at you, and you have to enter the steps manually (as opposed to having them programmed into an FMC). I wish I could remember some exact numbers, so what I will say here is just me going by admittedly faulty memory. To make a step climb, you intentionally level off at, say 26,000 feet. You allow the aircraft to get to cruising speed, and then you climb say 2,000 more feet. You allow the aircraft to gain speed, and do it again until you reach your target altitude. Jeff ShylukAvsim Product Reviewer

Insure that you have "Display indicated airspeed" selected on the Realism Settings page of the Aircraft menu. R-