On December 23, 2017, about 1415 Pacific standard time, an experimental, amateur-built Aircam airplane, N959M, was substantially damaged when it was involved in an accident near Newport, Oregon. The airline transport pilot received minor injuries, and the pilot-rated passenger was uninjured. The airplane was operated as a Title 14 Code of Federal Regulations Part 91 personal flight. The pilot reported that he planned to land on runway 2 at Newport Municipal Airport (ONP), Newport, Oregon. He recalled that the reported winds were from 090° at 9 knots. The airplane was stabilized on approach with a speed of about 76 mph and zero flaps. About 400 ft above the ground, the pilot felt a slight updraft and responded with an airplane-nose-down input to the flight controls. Very shortly thereafter, the pilot felt a significant, uncommanded "nose dip" and a rapid and significant left bank. The pilot applied control inputs in an attempt to correct, but the airplane had lost about 200 ft, its track had changed nearly 90° to the left, and the airplane appeared to be heading toward a building. The pilot focused on avoiding both the building and an aerodynamic stall but was unable to prevent the airplane from impacting trees. He estimated that from the time of the upset to the accident was 5 to 10 seconds. A GoPro Camera installed below the left wing revealed that the airplane was in a left turn to final for runway 2 at an indicated altitude of about 450 ft msl, descending about 200 ft per minute (fpm), with an indicated airspeed of 70 to 75 mph. A windsock located to the left of the runway 2 threshold was extended straight out and indicated about a 20° right crosswind. The airplane banked further left and began pitching nose down, and the pilot increased the engine rpm to 5,000. At that time, the altitude was about 250 ft msl, the airplane was descending about 250 fpm, and the indicated airspeed was about 70 mph. The airplane then pitched slightly up, and the pilot quickly retarded and then re-advanced the throttles. The indicated airspeed was just below 70 mph and the airplane was descending about 500 fpm. The pilot then retarded the throttles to idle as the airplane began striking trees. The airplane impacted the ground and came to a stop with both engines continuing to operate at high rpm. At all times, the tachometer showed that both engines were producing power and were synchronized in rpm. The pilot recalled that at least one of the engines continued to operate after impact, and in response he shut the engine(s) down and secured the cockpit. The airplane came to rest upright in a partially wooded area about 550 ft short of the runway's displaced threshold and about 650 ft northwest of the extended runway centerline. The airplane cut a swath about 75 to 100 ft long through the trees in a direction about 45° left of the runway alignment. Both floats were significantly damaged and displaced, and both wings were substantially damaged. Examination of the flight control system did not reveal any indications of pre-impact mechanical abnormalities. Aileron control cable continuity was established between the tandem cockpits and the flight control surfaces. Elevator control continuity between the aft cockpit control stick and the flight control surfaces was verified. The elevator control cable between the forward and aft cockpit was fracture-separated, consistent with impact damage. Rudder control continuity between the cockpits and the rudder was confirmed. Both fuel tanks were at least 1/4 full, and their caps were properly installed and secure. Both engines and their respective 3-bladed composite propellers were intact, and both propellers/engines could be rotated manually. There were no indications of pre-impact mechanical failures. The airplane was equipped with two engine data monitors. Both devices were successfully downloaded and contained data from the accident flight. Recorded parameters included exhaust gas and cylinder head temperatures for each of the four cylinders, fuel flow, fuel used, and battery voltage. None of these parameters provide a direct measure of engine rpm or power; however, both engines displayed normal operating temperatures throughout both recordings.