I go back to Flight Sim 1.0. I've owned every version since then. However, for nearly all of that time, I focused on flying props only in most GA situations.
Recently I decided to try and tackle flying the bigger jets (stock 737-400 and the 747). It's been a bit of a mess. First, I installed a file (I forget now which one I replaced) that works great starting everything in the game as turned off. All power is off, etc. I love doing manual starts, step-by-step.
The problem is that sometimes this leads to holes when I miss something. In props I'd forgotten to turn on the generators and about 30 minutes into flying the batteries would die without any indication and any battery-dependent equipment would "mysteriously" shut off. Took me a while to realize I'd never turned on the generators.
I provide all this detail due to the new problem. I have the jets the same way. I get in, power up the engines, switch on the Avionics and start flying. However, when I kick on the ATC and set Auto Throttle on and have my Nav and IAS selected (in addition to HDG and ALT or GPS nav) everything works great for a while and then suddenly the plane goes haywire and starts to literally fall out of the sky. All I notice is that the engines have entirely shut down. I have to quickly fight the plane into a glide, turn off all autopilot control and then manually re-set everything to get full control again. This happens twice during every flight. Once during ascent and worse during landing. Great time for both. Does anyone have ANY idea what might cause this or what I might be overlooking during start-up?