A plane left the runway at Danbury Municipal Aiport over the weekend and the cause is under investigation.  A small plane was landing Sunday afternoon when it traveled about 100 feet off the runway and into the grass.  The plane was coming in from Ocean City Municipal Airport in Maryland around 3pm.  The cause is undetermined at this time.  Officials says there were two people on board and neither were injured.  No massive damage to the aircraft was reported.  A tow company responded to move the plane off the grass.