The flight instructor reported that, during an instructional flight, while on short final, he told the student pilot to "pitch down" to maintain airspeed. He added that the student did not respond and he again instructed the student to "pitch down now" while simultaneously pressing forward on the yoke. He further added that as he pushed forward on the yoke, the student "pulled [back] with equal force on the yoke." Subsequently, the flight instructor pushed forward on the yoke "with greater force" than the previous attempt and stated, "my plane" to the student, but "continued to wrestle the controls with the student" as the airplane entered an aerodynamic stall and impacted the runway threshold hard. After the airplane impacted the runway threshold, the nose gear collapsed and the airplane veered off the runway to the right. The student pilot reported that this was his first flight ever with this flight instructor, but he had accumulated about 82 hours of dual instruction previously. He added that, during the second landing of the day, while on final approach "the instructor had me pull the power and told me nose down." He further added that he "felt we were getting low and I told the instructor I wanted to increase power but the instructor told me to "nose down." The student pilot reported that the instructor again stated multiple times to "nose down," but he "did not believe there was enough room to continue nose down." Subsequently, the student pilot reported that the flight instructor took the flight controls and nosed the airplane down, but the airplane impacted the runway threshold hard and veered off the runway. The fuselage and firewall sustained substantial damage. The flight instructor and student pilot reported that there were no preaccident mechanical malfunctions or failures with the airplane that would have precluded normal operation. During postaccident correspondence with the National Transportation Safety Board investigator-in-charge, the flight instructor reported that he could not recall during preflight that he and the student pilot discussed the positive transfer of the flight controls. The Federal Aviation Administration Advisory Circular 61-115, Positive Exchange of Flight Controls Program, dated March 10th, 1995, stated in part: During flight training, there must always be a clear understanding between students and flight instructors of who has control of the aircraft. Prior to flight, a briefing should be conducted that includes the procedure for the exchange of flight controls. A positive three-step process in the exchange of flight controls between pilots is a proven procedure and one that is strongly recommended. When an instructor is teaching a maneuver to a student, the instructor will normally demonstrate the maneuver first, then have the student follow along on the controls during a demonstration and, finally, the student will perform the maneuver with the instructor following along on the controls. When the flight instructor wishes the student to take control of the aircraft, he/she says to the student, "You have the flight controls." The student acknowledges immediately by saying, "I have the flight controls." The flight instructor again says, "You have the flight controls." During this procedure, a visual check is recommended to see that the other person actually has the flight controls. When returning the controls to the instructor, the student should follow the same procedure the instructor used when giving control to the student. The student should stay on the controls and keep flying the aircraft until the instructor says, "I have the flight controls." There should never be any doubt as to who is flying the aircraft.