Aside from the usual rules of social etiquette, there really aren't many rules or restrictions built into the coding of the FS Airpark website. Generally, if the site won't let you do it without some kind of workaround, it's probably against the "rules."
The rules listed below are based on the way things work in real aviation. In FS Airpark, just like in the real world, there isn't anyone standing over your shoulder to make sure you follow all the rules all the time. However, remember that your actions on the site are logged in a database, so there's a virtual paper trail. If you're suspected of violating the rules below, you could be investigated and face consequences up to and including termination of your account.
A current annual inspection is required for ALL flights. An annual remains valid until the end of the 12th calendar month following the inspection. An aircraft with an annual performed on December 1, 2013 will remain airworthy until December 31, 2014.
A commercial inspection is valid for 30 days following the date of the inspection. A current commercial inspection is required for all revenue flights.
It is the responsibility of the pilot in command to determine the airworthiness status of the aircraft before flight. Only the aircraft's owner is able to authorize an annual or commercial inspection.
Inspections can only be performed at airports with an active FBO. If an aircraft's inspections have lapsed and there is no FBO at its current location, the aircraft may be ferried via the most direct routing practical to the nearest FBO for the inspection. Such flights may not carry passengers or be logged for revenue.