Instructions
Download the FSX Cold and Dark Cockpit Mod from the Simviation website.
Open the location of your "Other" folder within the "Flight Simulator X" directory. By default, it is located at "C:\Program Files\Microsoft Games\Microsoft Flight Simulator X\flights\other."
Locate the "fltsim.flt" file. Select it and then press "Ctrl+C" and "Ctrl+V" to back it up. That way, if anything goes wrong, you have a copy of the original file.
Open the downloaded FSX Cold and Dark Cockpit Mod file using WinZip or WinRAR.
Find the "fltsim.flt" file within the downloaded folder. Drag and drop it into your "Other" folder to install the mod.
Start your "Flight Simulator X" game and select "Free Flight" from the game's menu. When it starts, your plane should be silent and powered off.