What happened
The FAA’s narrative, in sentence case. The FAA writes it in capitals and removes private details.
Pilot did not secure the aft passenger door prior to takeoff. The primary door latch was not secured and the secondary "safety" door latch was sticking and not engaging properly. There are two small carbon fiber type hinges made specifically to break off at low airspeed. Thus minimizing damage to composite structure. The door came open during takeoff ground roll breaking the two hinge points . The door fell off onto runway. No other damage to airframe or tail was found. Door open warning system was found to be functioning.
As the FAA filed it
PILOT DID NOT SECURE THE AFT PASSENGER DOOR PRIOR TO TAKEOFF. THE PRIMARY DOOR LATCH WAS NOT SECURED AND THE SECONDARY "SAFETY" DOOR LATCH WAS STICKING AND NOT ENGAGING PROPERLY.THERE ARE TWO SMALL CARBON FIBER TYPE HINGES MADE SPECIFICALLY TO BREAK OFF AT LOW AIRSPEED. THUS MINIMIZING DAMAGE TO COMPOSITE STRUCTURE. THE DOOR CAME OPEN DURING TAKEOFF GROUND ROLL BREAKING THE TWO HINGE POINTS . THE DOOR FELL OFF ONTO RUNWAY. NO OTHER DAMAGE TO AIRFRAME OR TAIL WAS FOUND. DOOR OPEN WARNING SYSTEM WAS FOUND TO BE FUNCTIONING.