What was found
DURING CRUISE FLIGHT AT 90 KNOTS, A LOUD POP WAS HEARD ON THE LT SIDE OF ACFT. DETERMINED THE CO-PILOTS DOOR OPENED PARTIALLY, DAYLIGHT COULD BE SEEN THROUGH LOWER FRONT OF DOOR INSTEAD THE REAR WHERE NORMALLY WOULD OPEN. SLOWED ACFT WHILE INSTRUCTOR HELD ON TO THE DOOR HANDLE. PERFORMED AN OFF AIRPORT LANDING. ABLE TO DETERMINE THE LOWER HINGE SNAPPED IN HALF AT HOLE WHERE ATTACHING PIN PASSES THROUGH. REMOVED DOOR, AND RETURNED TO THE AIRPORT.