 Following the testing at Yuma , prototype # 9 received the improved T64 @-@ GE @-@ 716 engine producing 4 @,@ 275 shp ( 3 @,@ 188 kW ) and the planned production version of the ICS system . With 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 . 
