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A-9
Role	Attack aircraft
Manufacturer	Northrop
First flight	1972-05-20
Status	Cancelled
Primary user	NASA
Number built	2

The Northrop YA-9 was a prototype attack aircraft developed for the USAF, but passed over in preference for the Fairchild YA-10 that became the A-10 Thunderbolt II in service.

[edit] Design and development

Both aircraft were designed in response to the A-X air force requirement for a Close Air Support (CAS) aircraft that could operate from forward positions on a battlefield. This meant an aircraft that would need to be able to operate from relatively rough fields, carry heavy armor, and be able to loiter over target areas. It was purpose-built modern replacement for the A-1 Skyraider which could perform the ground attack mission over Vietnam more effectively than faster supersonic jets. While turboprops were considered in some designs for the A-X project, turbofans were selected for the flyoff prototypes. The A-9 used the Lycoming F-102 engine, while the A-10 used the GE TF34 as used in the contemporary S-3 Viking and proposed for use in the E-3 Sentry.^[1] The YA-9 saw its first flight May 20, 1972.

Apart from aircraft themselves, the A-X program was also developing a powerful cannon for the winning plane to carry. Eventually, this would result in the GAU-8 Avenger, but for trials, the YA-9 and YA-10 were both equipped with the smaller M61 Vulcan Gatling gun. By comparison, the A-10 engine location at the tail is less conventional, but offers greater survivability in the case of a hit on the engine area. The double tail of the A-10 also hides the engine infrared and noise signature, and is redundant in case one of the tails is shot away.

A fly-off of the two prototypes took place between October 10 and December 9, 1972, with the YA-10 declared the winner on January 18, 1973. The two YA-9 prototypes were subsequently relegated to NASA for continued flight testing before being quickly retired. When retired, the YA-9s' custom-built engines were removed and were later mated to a C-8 Buffalo airframe as part of the NASA-Boeing joint QSRA study into a quiet short-haul commercial aircraft.