What happened
The FAA’s narrative, in sentence case. The FAA writes it in capitals and removes private details.
Upon conducting a commercial mult-engine lesson in 882L, a rear door separation occurred. Prior to startup, the rear door was closed and latched and confirmed by both pilots. Annunciations were checked prior to takeoff with no "door open" annunciation noted. Takeoff was normal with no abnormalities noted. Upon reaching cruise flight at 2500FT and accelerating to cruise speed, it was noted that there was an abnormal sound of airflow occurring. Inspection of the rear door revealed that it was partially opened. The CFI attempted to close the door, however upon touching the door it opened and separated from the aircraft. No damage to the airframe as a result of door separation was felt, and flight controls were not compromised in any way. A pan pan declaration was made, and the flight returned to kmyr without furthur incident. The door separation occurred approximately 5 miles to the south east of kmyr, and approximately 0.5-1.0 NM off shore over the ocean. There were no injuries.
As the FAA filed it
UPON CONDUCTING A COMMERCIAL MULT-ENGINE LESSON IN 882L, A REAR DOOR SEPARATION OCCURRED. PRIOR TO STARTUP, THE REAR DOOR WAS CLOSED AND LATCHED AND CONFIRMED BY BOTH PILOTS. ANNUNCIATIONS WERE CHECKED PRIOR TO TAKEOFF WITH NO "DOOR OPEN" ANNUNCIATION NOTED. TAKEOFF WAS NORMAL WITH NO ABNORMALITIES NOTED. UPON REACHING CRUISE FLIGHT AT 2500FT AND ACCELERATING TO CRUISE SPEED, IT WAS NOTED THAT THERE WAS AN ABNORMAL SOUND OF AIRFLOW OCCURRING. INSPECTION OF THE REAR DOOR REVEALED THAT IT WAS PARTIALLY OPENED. THE CFI ATTEMPTED TO CLOSE THE DOOR, HOWEVER UPON TOUCHING THE DOOR IT OPENED AND SEPARATED FROM THE AIRCRAFT. NO DAMAGE TO THE AIRFRAME AS A RESULT OF DOOR SEPARATION WAS FELT, AND FLIGHT CONTROLS WERE NOT COMPROMISED IN ANY WAY. A PAN PAN DECLARATION WAS MADE, AND THE FLIGHT RETURNED TO KMYR WITHOUT FURTHUR INCIDENT. THE DOOR SEPARATION OCCURRED APPROXIMATELY 5 MILES TO THE SOUTH EAST OF KMYR, AND APPROXIMATELY 0.5-1.0 NM OFF SHORE OVER THE OCEAN. THERE WERE NO INJURIES.