HISTORY OF FLIGHTOn March 18, 2013, about 1515 Pacific daylight time, a Piper PA-23-250, N318CA, departed the end of the runway following a rejected takeoff from Stark's Twin Oaks Airpark, Hillsboro, Oregon. The airplane was registered to Twin Oaks Airpark, Inc., and operated by the private pilot as a local instructional flight under the provisions of 14 Code of Federal Regulations Part 91. The certified flight instructor and private pilot undergoing instruction were not injured. The airplane sustained substantial damage to both wing spars and the forward fuselage structure during the accident sequence. Visual meteorological conditions prevailed, and no flight plan had been filed. The flight was to be the private pilot's first multiengine lesson. Both he and the instructor reported performing an uneventful preflight check, brake check, and engine run-up. They confirmed that the door was closed and locked, and the flight instructor inflated the door seal, and checked that the parking brake was disengaged. The private pilot positioned the airplane at the end of the runway, and applied full engine power. Both he and the instructor stated that once the airplane approached a speed of 80 mph, and just prior to rotation, the right cabin door opened about 1 inch. They had travelled about 1/3 of the way down the runway at that time, and the flight instructor called for the pilot to abort the takeoff. He reduced engine power to idle, and applied pressure to the brake pedals. The flight instructor stated that the airplane began to decelerate, however, a few seconds later she became concerned that they would not be able to stop in time on the remaining runway. The private pilot felt the airplane decelerate, however, as they approached the end of the runway, brake effectiveness began to dissipate. The airplane subsequently overran the runway, coming to rest in a ditch. Two witnesses provided corroborating statements regarding the accident sequence, that during the takeoff roll both engines went to idle about 1/3 of the way down the runway. They observed the airplane begin to decelerate, assuming it would stop in time; however, it continued, ultimately departing the runway end at a walking pace. The airplane was not equipped with foot brakes on the right side, which was occupied by the flight instructor. PERSONNEL INFORMATIONThe flight instructor held an airline transport pilot certificate, and reported a total flight experience of 9,368 hours, 5,440 of which was in multiengine airplanes, and 5.1 in the accident make and model. She further reported 3,551 hours as a flight instructor, 74 of which was in multiengine airplanes. The pilot undergoing instruction held a private pilot's license, with ratings for single-engine land and instrument airplane. He reported a total flight experience of 191.4 hours, all in single-engine airplanes. TESTS AND RESEARCHAccording to the flight instructor, the airplane's gross weight at the time of the accident was 4,230 pounds. The applicable flight manual provided an accelerate-stop distance performance chart. Utilizing the weather conditions and airplane's weight after reaching an indicated speed of 80 mph, with zero flaps on a level dry paved runway, the distance required would have been about 1,800 feet. The manual did not provide factors for runway slope. The Emergency Procedures section of the flight manual provided the following procedure for closing the cabin door in flight: "In the event the cabin door is inadvertently unlocked in flight or the handle is not pushed forward and locked before take-off and becomes dislodged from its latching position, the following procedure has been determined to be practicable for closing the cabin door while in flight, assuming adequate altitude has been attained. a. Retard throttles. b. Reduce airspeed to 90 MPH or less. c. Open storm window (left of pilot). d. Close door. e. Recover power and airspeed." The manual further stated that should the door become unlocked during take-off, landing approach, and general low altitude flight, the required action will be at the discretion of the pilot. The FAA inspector performed an examination of the airplane's brake system following the accident, and reported no mechanical failures or anomalies which would have precluded normal operation. When asked about the decision to abort the takeoff, the flight instructor stated that she had heard anecdotal evidence from other flight instructors that the airplane type was hard to control if the door opened in flight, so she chose to abort the takeoff rather than risk having a flight control problem after departure.