On August 24, 2016, about 1800 Pacific daylight time, a Siai-Marchetti SF260 airplane, N16FD, was substantially damaged when it was involved in an accident near Fullerton, California. The airline transport-rated pilot and passenger sustained minor injuries. The airplane was operated as a Title 14 Code of Federal Regulations Part 91 training flight. The flight was operated by Air Combat USA, as an aerobatic customer training flight. The pilot, who was a current fighter pilot and instructor in the F/A-18A-D with the United States Marine Corps, had about 7.6 hours of flight experience in the accident airplane type, and the flight was intended to familiarize him with the handling qualities of the airplane type with a passenger on board. The passenger, who was an employee of Air Combat USA, had about 60 hours of flight experience, but did not hold a pilot’s certificate. The pilot reported that the preflight, taxi, and initial takeoff roll were all normal. During the takeoff roll, just after rotation, the airplane began to roll left. The pilot attempted to correct for the roll by adding full right aileron and rudder, but the airplane continued to roll to the left and impacted the ground off the left side of the runway. After the airplane impacted the ground, it continued to travel across a flight school ramp, struck a taxiing airplane and three parked airplanes, and impacted a hangar before coming to rest. A small postaccident fire ensued and was quickly extinguished by airport personnel. Postaccident examination of the airframe and engine revealed no anomalies that would preclude normal operation. Four recovered video files were sent to the NTSB Vehicle Recorder Division for analysis. At the start of one video, which was recorded by an onboard video camera system that recorded high-quality audio from the airplane’s intercom and alternately from two cameras: one faced aft towards the pilots and the other faced forward from behind the pilots. The aft-facing camera recorded that, just before the airplane taxied to the hold short line, the left flap was visible and appeared to be in the retracted position. The system then switched to the forward-facing camera as the airplane taxied unto the runway as the second airplane in the formation. The pilot and the passenger discussed the takeoff but make no mention of the flap position. The operator knew before the accident flight that the airplane’s flap gauge was inoperative. Therefore, the flaps were set to the takeoff position by matching them to a fully deflected aileron on the same side of the wing. Using this technique to set the flaps for takeoff in a same type of airplane with a functional flap gauge, the flap setting was observed to be about 17°. The airplane’s operations manual states that the takeoff flap setting is 20°. Furthermore, the manual and the Before Take-off checklist state to set flaps to 20° before takeoff. The other videos were taken from cameras on the airport ramp and captured the accident airplane’s path. Review of one of the videos revealed that, about 4 seconds after the cameras began recording, the airplane was on the runway and accelerating. About 3 seconds later, the nose gear and left main gear were clear of the runway, and the airplane banked slightly to the right. About 2 seconds after that, the airplane was airborne and pitched up slightly and was rolling to the left; 1 second later, the left bank increased to about 15°. The video ended at 2 seconds after that, with the airplane left of the runway, and in a left bank of about 10-15°. The next video showed the airplane taking off but did not gain altitude after becoming airborne. About 22 seconds after the cameras began recording, the last video captured the airplane passing over parked airplanes, possibly striking one. The accident airplane came to rest 2 seconds after that, followed by a plume of smoke. Another video that was reviewed by the NTSB investigator-in-charge showed the lead airplane taking off followed by the accident airplane taking off. Figure 1: Accident airplane’s takeoff flap position. Figure 2: Exemplar airplane’s flaps set to takeoff position. A Federal Aviation Administration inspector examined and took pictures of an exemplar Siai-Marchetti SF260 airplane and observed the flap position from a rearward angle, which was similar to the angle of the accident airplane’s video camera that faced rearward (see figures 1 and 2). The examination revealed that when the flaps were set to the takeoff flap setting of 20°, the flaps were easily discernable to be partially extended, in the exemplar airplane, which is the same type as the accident airplane.