Originally Posted by
LowObservable
Historical note: the AH-56 itself survived the Air Force's challenge, emerging unscathed from the 1971 Senate review of different service CAS requirements. I believe it was the Army's decision, in the light of technical problems and combat experience, to replace the AH-56 with the AAH, which became Apache.
What killed Cheyenne was USAF General Momyer's (commander, Tactical Air Command) who cited the helicopter casualty statistics at Operation Lam Son 719 during Senate testimony. This forced the Army to convene a special task force in 1972 under Army General Marks to reevaluate their requirements for an attack helicopter and develop an "updated and defensible" material needs document. This was followed by a weapons demonstration for the Senate Armed Services Committee. Sadly the first TOW missile failed and flew into the ground. Even though this was a missile failure and not a fault of the launch platform, the Cheyenne was tainted by the failure. The Senate's report on CAS then recommended to fund USAF's A-X and USMC's Harrier programs, but was silent on the Cheyenne and lukewarm at best on the general subject of attack helicopters with a requirement that their survivability be improved. Three months later (August 1972) Cheyenne was cancelled and the Army's AAH program launched a week later. The AAH was a pure helicopter and USAF had no grounds to oppose it. That program resulted in the Apache.
And then Cheyenne #7 with the new AMCS (advanced mechanical control system) flew and showed it had resolved the Cheyenne's controllability and stability issues, improved handling, improved maneuverability, and reduced pilot workload. It also reached a speed of 215 knots in level flight and 245 knots in a dive, very good numbers to this day. But Cheyenne was dead as a program. Lockheed tried to resurrect it by competing for AAH with a modified Cheyenne with two engines and no pusher prop, but failed. And this killed Lockheed's attempt to get into the helicopter market. McDonnell Douglas used a different approach to get into that market. It bought Hughes Helicopters which had a line of both commercial and military helicopters. But McDonnell never understood the commercial aviation business and ended up slowly killing both their commercial airliner and helicopter businesses by failing to invest.