Funny you mention the A-4, as there is currently a free mod in development, which was made by developers who do not have access to the full SDK (toolset) of third parties due to the fact it is freeware, and what they made is almost the complement of FC3-level.
In FC3 the cockpit is not clickable and the systems operation is not like in the real aircraft but the flight model and systems relevant for flight are extremely accurate.
In the community A-4E mod the cockpit is clickable, systems like radar and weapons are operated like the real thing, but the flight model and systems are simplified.
The only thing they have in common is great graphics.
EDIT: Here is a link to the Mudspike summary of the ED forums thread.