these upgrades, the helicopter surpassed its performance requirements. However, under certain conditions stability and control did not completely satisfy the test pilots. Lockheed had studied ways to prevent unstable feedback from the gyro. The solution was to relocate the gyro from the top of the rotor head to below the transmission with flexible connections to the rotor. The pilot's controls were connected to hydraulic servomotors then connected through springs to the gyro. This system prevented rotor vibration forces from transmitting back into the flight controls. It was called the "advanced mechanical control system" (AMCS) and was installed on Cheyenne #7 in 1972 to improve handling and rotor stability. Program demise In 1971, political friction increased between the Army and the Air Force over the close air support (CAS) mission. The Air Force asserted that the Cheyenne would infringe on the Air Force's CAS mission in support of the Army, which had been mandated with the Key West Agreement of 1948. The Department of Defense (DOD) conducted a study that concluded that the Air Force's A-X program, the Marine Corps' Harrier, and the Cheyenne were significantly different that they did not constitute a duplication of capabilities. On 22 October 1971, the Senate Armed Services subcommittee on Tactical Air Power conducted hearings to evaluate the CAS mission and the pending programs. The most damaging testimony for the Army's program came from the commander of the Air Force's Tactical Air Command, General William W. Momyer, who cited helicopter casualty statistics of Operation Lam Son 719. The Army convened a special task force under General Marks in January 1972, to reevaluate the requirements for an attack helicopter. The purpose of the Marks Board was to develop an "updated and defensible" material needs document. The task force conducted flight evaluations of the AH-56, along with two industry alternatives for comparison: the Bell 309 King Cobra and Sikorsky S-67 Blackhawk. Analysis of the three helicopters determined that the Bell and Sikorsky helicopters could not fulfill the Army's requirements. The Army also conducted a weapons demonstration for the Senate Armed Services Committee in early 1972, to show off the Cheyenne's firepower and garner support for attack helicopter development. The first TOW missile that was fired in the demonstration failed and went into the ground. The second missile was fired and hit the target. Previously, 130 TOW missiles had been fired without failure, but the failure of the