...When ever I load a new flight with the aircraft being properly shut down and secured after the previous flight, the aircraft is being loaded with the battery on and the engine running.
There are a couple of things you can try that might fix this:
1. Creat a Cold and Dark state for your default aircraft. If your FSX always wants to start you in a Cessna 172 at Seattle, open that flight and turn off the engine. Once everything is shut down, Save this flight using the menu at the top of the screen (hold the Alt key to activate to make the menu bar visible). You can also save by hitting the semi-colon key. Make sure you check the box that is marked "Make this default flight." Now all or your Fly Now flights should start in Cold and Dark condition.
2. Save your P-51 flight as a different file from the default flight once you have shut the engine down. Every time you load this flight, the engine should be off. However, it will always be the same time, date, location and weather as the last time you saved. Not all Accusim Cold and Dark conditions will save though, so you'll probably have to hit C&D after reloading anyhow.
I use both options all the time. The first gives me a universal state where all Fly Now scenarios start with the engine(s) off. The second allows me to fly and land, save, and return later to find my chosen aircraft exactly where I left it.
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