tests, a rotor instability issue was discovered when the aircraft was flying at low altitude in ground effect. As the flight envelope was expanded, this instability and other minor problems were discovered and quickly addressed. Lockheed and the Army held a 13-minute demonstration "first flight" for the public at the Van Nuys Airport on 12 December 1967. During the flight, the Cheyenne demonstrated some of the new capabilities brought about by the thrusting propeller; the helicopter could slow down or accelerate without pitching the nose up or down, as well as being able to pitch the nose down or up at a hover, without causing the aircraft to accelerate forwards or backwards. The Cheyenne demonstrated a stationary hover in a 30-knot (35 mph, 56 km/h) crosswind, and at the end of the flight landed on its two forward landing gear, "bowed" to the audience and then gently set the tail landing gear down as it taxied to parking. By March 1968, the AH-56 had established a flight envelope of 170 knots (196 mph, 315 km/h) in forward flight, 25 knots (29 mph, 46 km/h) sidewards, and 20 knots (23 mph, 37 km/h) rearwards. The project suffered a setback on 12 March 1969, when the rotor on prototype #3 (s/n 66-8828) struck the fuselage and caused the aircraft to crash, killing the pilot, David A. Beil. The accident occurred on a test flight where the pilot was to manipulate the controls to excite 0.5P oscillations (or half-P hop) in the rotor; 0.5P is a vibration that happens once per two main rotor revolutions, where P is the rotor's rotational speed. The accident investigation noted that safety mechanisms on the controls had apparently been disabled for the flight. The investigation concluded that the pilot-induced oscillations had set up a resonant vibration that exceeded the rotor system's ability to compensate. After the investigation, the rotor and control systems were modified to prevent the same problem from occurring again. Production contract canceled The Army issued a cure-notice to Lockheed on 10 April 1969, citing 11 technical problems, and unsatisfactory progress on the program. The main issues were the half-P hop vibration issue, and the aircraft gross weight exceeding program requirements. In response, Lockheed proposed an "improved flight control system" (ICS) to reduce rotor oscillations, and steps for removing excess weight and addressing other minor issues in production helicopters. The Army felt Lockheed's solutions to