Piaggio PD-808RM

History (courtesy of Wikipedia):
The Piaggio PD.808 was designed by the Douglas Aircraft Company of Long Beach, California, as a business jet. No orders were received, and the complete project was bought by Piaggio, which flew the first prototype in August 1965. Piaggio also failed to secure any worthwhile commercial interest, but a few examples were taken by the Italian Air Force.
Only 24 examples of this type, with low-set wings and aft-mounted turbojet engines, were produced, and 22 of these went to the Italian Air Force. The first aircraft were configured for the utility role, but the last six aircraft were completed as electronic platforms with cabin accommodation for specialist electronic intelligence equipment and its three operators.
The Addon:
This FS2004 representation, produced as freeware by Mario Noriega, is what I consider to be a top-notch simulation of a relatively unknown aircraft.
This aircraft is filled to the brim with special features, and some unique systems simulation, which, in my opinion, create a nice balance between complexity and single-pilot usability.
(There is also a separate version for FSX!)
Cockpit/Systems:

To get to the point: You can start this aircraft just as you would