 Lockheed worked on modifying the AH @-@ 56 design to address the vibration and other issues . As a precaution , Cheyenne # 9 ( s / n 66 @-@ 8834 ) was fitted with an ejection seat for the pilot after the March accident . The downward firing ejection seat was placed in the forward seat in place of the gunner 's station . This prototype would be used for all remaining envelope expansion flights . Prototype # 9 also received an upgraded transmission and drivetrain , and a hinged rear canopy in place of the original sliding canopy around 1970 . The new transmission allowed the T64 @-@ GE @-@ 16 turboshaft engine output to be increased from a derated 3 @,@ 435 horsepower ( 2 @,@ 561 kW ) to 3 @,@ 925 horsepower ( 2 @,@ 927 kW ) , and the new canopy eliminated the canopy vibrations . 
