This is a short note on 'stalling aircraft' when you use them in FSX or P3D. 
Maybe you have experienced that one too: 
After takeoff, your aircraft climbs out with the predefined climb rate (usually 1500 ft/min) nicely.
At higher altitude you suddenly go into a stall which can not be recovered by FSXPilot.
When we googled the problem, we found out that in real the big jets use an initial climb rate of 3500 ft/min , but they have to reduce that to 2000 ft/min above 10000 feet and reduce it even more the higher they climb. The same is true also for smaller aircraft. 
So please make sure that you fly with adequate speeds and reduced climb rates above 20000 ft ! With a B747 I would recommend to do the climb between 25000 and 35000 feet with 800 ft/min and increase IAS to 320 knt to avoid any stall. 
In version 1.51, we implemented a new flightplan command
set waypointclimb xxxx
which can be used prior to any waypoint command in a flightplan. See the EDDM to EDDF demo flightplan in the flightplan directory for an example.  
You can now start out really steep and gradually reduce the climb rate during the flight plan.
Works nice !