On March 6, 2018, about 1005 eastern standard time, a Piper PA-28-140, N6764W, was substantially damaged when it impacted terrain while on approach to Massey Ranch Airpark (X50), Edgewater, Florida. The flight instructor and student pilot were seriously injured. The airplane was privately owned and operated as a Title 14 Code of Federal Regulations Part 91 instructional flight. Visual meteorological conditions prevailed at the time of the accident and no flight plan was filed for the local flight.According to a witness, who was also a pilot, the airplane was on the final approach leg of the airport traffic pattern at "low" altitudes on the previous landing while doing pattern work. The airplane descended below the treeline, the witness perceived that the airplane's engine power increased before it cleared the treeline prior to continuing the final approach. The witness then left the airport and did not witness the accident sequence. The pilot and passenger reported to a Federal Aviation Administration (FAA) inspector that due to the injuries they sustained during the accident, they had no recollection of the events preceding the accident. Examination of the airplane by the FAA inspector revealed that it impacted the ground in a nose down attitude about 750 ft prior to the threshold of runway 18. The top section of a tree was separated and located beneath the wreckage. In addition, there were several small branches with 45° cuts in them. The inboard section of the left wing was impact crushed aft and the left-wing tip was impact crushed. The outboard section of the right wing was impact crushed aft. The empennage was buckled and the horizontal stabilator and rudder remained undamaged. A total of 25 gallons of aviation fuel was noted in the wing fuel tanks during recovery. An examination of the engine by an NTSB investigator revealed that it remained attached to the engine mounts. Thumb compression was obtained on all cylinders and crankshaft and valve train continuity were confirmed through the engine and accessories by rotating the propeller through 360° of rotation. The left and right magnetos produced spark on all ignition towers during hand rotation. The propeller remained attached to the engine and chordwise scratching was noted on the blades. The oil suction screen was free of debris and about 4.5 quarts of oil were noted in the engine per the oil dipstick. The carburetor inlet screen and the main fuel strainer were examined and free of debris. A review of the airframe revealed that flight control continuity was confirmed from the flight controls to the respective flight control surfaces. The fuel selector was tested with low pressure air and no anomalies were noted. There were no anomalies noted with the airplane that would have precluded normal operation prior to the accident.