The PSS Airbus is pretty amazing in terms of detail. Every aspect of the start-up procedure (from cold, or using external power) is there, and if you use it with S-Combo, you can have some pretty realistic results.
As well as the extensive startup procedure, you're in total control of the FMC as well - you program the waypoints of your flight, as well as fuel loads, and V-speeds. It's pretty incredible, actually!
Hey...psst. Did you forget to read this in the tread creator's message
"hi there,
does anyone know of a
freeware addon aircraft that is a detailed and involving as the Fanda Dash 8?"

PSS Airbus isn't freeware, nor will it ever be...