What are the legal consequences for an airplane that experiences a Runway Incursion?

What you described is formally referred to as a runway incursion, which is defined by the FAA as "any occurrence at an aerodrome involving the incorrect presence of an aircraft, vehicle or person on the protected area of a surface designated for the landing and take-off of aircraft."  Unfortunately, runway incursions are happening more often, particularly with smaller aircraft, and lives are at risk whenever they occur.  Incursions usually occur through controller error, pilot error, or vehicle driver error.  Where a pilot is at fault, anything from distractions, disorientation, to basic incompetence may be the cause.

Following any incursion, the FAA conducts an investigation to determine who is at fault and why the incursion happened.  If the violating pilot is cooperative, and the incursion did not result in an accident, the FAA usually does not pursue a civil penalty action or suspension.  In such cases, the pilot may receive a warning and have to complete corrective action.  However, if the incursion arose because of a lack of qualification, the FAA may pursue a re-examination or even license revocation against the pilot.

To understand more about runway incursions, consult the FAA website on general airway safety regulations.  As you have been personally involved in an airway incursion, you should also consult with an attorney to determine any issues that might arise.