Hay what UP,ok! heres something new for me and I hope you can help me.I setup A flight from RJBB - KDEN, FL40000, IFR, No Dep. speed restriction and I'm using Radar Contact. I take off with IAS set to 350kt. at FL10000 ft. I set the IAS 450kt. with VS set to 1500ft. at FL16000ft. I set the VS to 1800ft.Now here's the good part, at or about FL25000ft. I set the IAS to 500kt. at VS 1800ft. I climb to about FL30000ft. or so. And its down hill from here on, first it never gets pasted IAS 450kt..The Aircraft starts to loose its speed very slowly and the nose pitchs up, I'm sure you know what happens next!I'm all over the sky in A bad spin and the next thing I know ( KA BOOM ) its all over.This happens with all of the Aircraft in FSX but it don't always get into A spin and I don't always bite the dust. I wrote all of this just to ask you one question ( :-zhelp ).. Please tell me what am I doing wrong or do I need to fix or correct something? This is driving me nuts. :-vuur Thanks.Danny

INDICATED air speed is just that - and it varies with pressure and altitude. Above 25,000 feet or so, you switch to MACH hold NOT IAS, and the airrcfat will maintain the same ground speed, even though the IAS continues to decline.http://en.wikipedia.org/wiki/Indicated_airspeedAllcott

Agreed, your problem is using kts at high altitude. None of the FSX aircraft will fly at 400 or 500 kts at 40,000 ft. You may get 280 or so and thats about it. Use MACH .78 to .82 when above 25,000.

An IAS of 500kt @ FL250 would be extremely unusual for an aircraft which is not a military high performance bird.Are you sure you are not looking for/ at TAS or ground speed?The default B747 can not be flown above 355kt IAS at any altitude or it will overstress and crash. At FL250 the B747 can only fly at or below Mach 0.59.But that has probably has nothing to do with your main problem of noseup, spin and crash.That sounds like the classic Pitot Tube freeze.There is a switch in your cockpit to turn on "Pitot Heat". Most of the time FS will simulate the pitot freezing closed near FL250 - even though real world weather conditions would not do so.The Pitot tube feeds the IAS reading instruments on the aircraft.Your auto throttle and many other parts of the auto pilot will fault if you do not have an IAS reading.The slowing airspeed (when viewed with Shift+Z) nose high pitch as the altitude hold tries to keep the aircraft at altitude and spin / crash are classic symptons of the Pitot Tube freeze closed.