Aerofax: Lockheed Martin F/A-22 Raptor, by Jay Miller, Midland Publishing 2005, ISBN 185780158X
YF-22 and YF-23 Advanced Tactical Fighters: Stealth, Speed and Agility for Air Superiority, by Bill Sweetman, Motorbooks International 1991, ISBN 0879385057
World Air Power Journal, Vol 7, Autumn/Winter 1991, p32-41, 'Northrop/McDonnell Douglas YF-23: The Fighter They Didn't Want', by Bill Sweetman
Joe Baugher's website

26 Jan 1973 The first formal requirements document   was issued. At this stage, more emphasis was given to multi-role ability since the fighter role was well taken care of by the F-15 and F-16, which were just about to reach operational status.

1976 Two F-15A Eagles were acquired for use by NASA's Dryden Flight Research Center for numerous experiments relating to digital control of aircraft functions. Although the GD's F-16 succesfully pioneered a fly-by-wire system for flight control, the ATF programme would take the use of digital control to the next level by extending the technology to all control systems, including the engine throttle. The related programmes that the F-15's flew in were called Highly Integrated Digital Electronic Control (HiDEC), Adaptive Engine Control System (ADECS), Self-Repairing and Self-Diagnostic Flight Control System (SRFCS) and Propulsion Controlled Aircraft System (PCA). The results of these tests led to the specification of a high level of integration in the avionics and control architecture planned for the ATF.

1979 American recce satellites detected new Russian fighter prototypes at Ramenskoye. They were code-named 'RAM-L', which would become the MiG-29, and 'RAM-K', which would become the Su-27. With the entry into service of these impressive new fighters, which were more than a match for the USAF's F-15 and F-16, the writing was on the wall.

April 1980 A Program Managment Directive (PMD) for Combat Aircraft Technology  was issued placing more emphasis on the air to air role.

1981 The idea of broadening the application of stealth technology by incorporating it into a high performance fighter began to be discussed in public for the first time, within the framework of the AIAA. Northrop published a paper that showed how a stealth fighter could see its opponent first and fire first, even if the adversary had a more powerful radar and longer range missile. A McDonnell Douglas paper emphasised STOL, stealth, and supercruise as desirable attributes in a fighter.

21 May 1981 A provisional Request For Information (RFI) was issued by the Air Force. 9 companies responded: Boeing, Fairchild, General Dynamics, Grumman, Lockheed, McDonnell Douglas, Northrop, Rockwell, and Vought.

June 1981 An RFI for an engine was issued. This early request was prudent in the light of previous Air Force experience, where engine development had always lagged behind airframe development, often hampering overall progress and service entry of the aircraft. The requirements were for: sufficient thrust for supercruise, STOL ability in 1,500 ft of runway, integration of Low Observable (stealth) technology, reduced cost of ownership, and an Intial Operational Capability (IOC) by 1993.

23 November 1981 The programme was given what was known as 'Milestone Zero' approval, becoming a formal weapons acquisition programme. It was written at the time: "The ATF Program is clearly threat and cost driven. Although uncertainty exists about the future threat, we must be technologically ready when a threat-driven development decision is required. Also, we must be fully aware of the cost trade-offs and we must know what must be given up to purchase each additional increment of capability. The program is structured to answer these questions." This was the first indication of the criteria that would be used to evaluate the winning bidder.

October 1982 An unclassified conference on the ATF programme took place in Anaheim CA. Some of the requirements were fleshed out: a 50,000lb 'counter-air' fighter, to land/take off from a bomb-damaged runway in 2,000 ft, a combat radius of 700-920 miles, supersonic cruise without the use of afterburner, low observability by hostile radar or infra red sensors if possible, and to be easier to support than an F-15 Eagle.

December 1982 $23 million was allocated to the ATF programme by Congress.

1983 The ATF System Programme Office under the Aeronautical Systems Division of the USAF was formed at Wright Patterson AFB in Ohio, with Colonel Albert Piccirillo as the ATF SPO Director. Its task was to produce a comprehensive specification which met the USAF's essential requirements, and as many of their 'desirables' as possible. "Early in this stage, we found 4 or 5 significant drivers. Meeting just one of them cost us 10,000lbs". In some cases, "backing off by 0.5% was important", Piccirillo stated. Col Piccirillo compared the use of stealth to the emergence of the U-Boat in W W I: "To kill without being seen, disengage and disappear. The last thing you do is surface and use the deck gun. Close-in combat is something you try to avoid. There's a big luck factor in a dog fight. 90% of people who get shot down and come back, never saw who shot them down." Northrop revealed a joint concept study at the Paris Airshow done in partnership with Dornier in Germany since 1978, called the ND-102, a light fighter with a trapezoidal wing and no tailplane, but with vectored engine thrust. Although not related to ATF, this design would prove to be highly influential on ATF design configurations.

18 May 1983 A formal RFP was issued to engine manufacturers as the Joint Advanced Fighter Engine (JAFE) contract. This RFP included a requirement for a 30,000lb thrust range capability.

26 May 1983 A RFP amendment was released that placed greater emphasis on stealth.

September 1983 GE & P&W were awarded $550 million contracts to build and test static engine prototypes. The engines were known in house as the GE37 and PW5000 respectively.

1984 The USAF HQ approved an ATF Statement of Operational Need (SON). The ATF requirement was refined and clarified. The core of this requirement was to achieve unprecedented levels of sustained cruise speed using economical fuel burn, and a reduction in the detectability of the aircraft by radar compared to previous fighters. The USAF had covertly conducted several research programmes into the feasibility of stealth and had fielded a practical strike aircraft, the F-117, so it was confident that this technology could be applied to a high performance fighter. It was assumed at the time that the new fighter would be compelled to operate from bomb damaged runways and would need the ability to take off and land in a distance considerably less than the full length. There was the intent to curb the escalating cost of fighter procurement was well. The SON called for a 5th Generation fighter with the following parameters:

In Flight Performance:
a combat radius of approx 800 miles

supersonic cruise, including:
the ability to cruise at Mach 1.4-1.5 when in hostile territory 
the ability to accelerate from Mach 0.6 to Mach 1 in 20 seconds
the ability to accelerate from Mach 0.8 to Mach 1.8 in 50 seconds at 20-30,000 ft

supersonic manoevure, including:
2 g turn sustained at Mach 1.5 and 50,000 ft
5 g turn at Mach 1
6 g turn at Mach 1.5 and 30,000 ft,
9 g turn at Mach 0.9 and 10,000 ft for 30 secs

In Logistics:
the ability operate from 2,000 ft of runway
compatibility with existing infrastructure including HAS 
the ability to carry existing air to air weapons
to have double the F-15 sortie rate , halved turnaround time to 15 minutes, and ability to fix 75% of faults in 4 hours
(At the time, the USAF employed maintenance staff trained in about 25 specialised tasks. The goal for the ATF was 8-10 specializations. There was also to be a simplification from a 3-level maintenance system to 2-level.)
to have modular reconfigurable avionics
a gross take-off weight of 50,000lbs 

In Economics:
Individual aircraft price capped to $40 million in 1985 dollars based on a production run of 750 aircraft 
Total Life Cycle Cost  comparable to the F-15
A total programme cost of $65 billion.

In addition:
Avionics were to be integrated to a higher level than previous generation fighters, fused sensor data was to be displayed to the pilot, thrust reversers were to be employed to augment in flight manoevurability and to facilitate the runway requirement, and it had to have a dramatically reduced radar signature compared to 4th generation fighters. Most performance parameters were expressed in 'required' and 'desired' values, but were matched with a cost ceiling which ruled out any attempt to achieve 'desired' values in all categories at once.

William J. Cook wrote, "Despite their complexity, ATF's actually will be easier to support and maintain in the field than current fighters, one of the Air Force's key requirements. The on-board flight computers will be capable of analyzing the plane's various mechanical systems, producing a list of specific problems that require attention. Each plane will carry its own auxiliary power supply: a small turbine-powered generator - to eliminate the need for a starting cart to crank its engines. The planes will be able to generate oxygen for the pilots and fire-suppressing nitrogen for the fuel tanks and weapons bays while in flight, eliminating the need to replenish supplies on the ground. All of this means that the equipment needed to maintain an ATF squadron could be deployed to remote combat locations on roughly half as many transport aircraft as are now needed. And if the ATF turns out to be as reliable as the Air Force projects, it will be able to fly more combat hours a day than present models, reducing the number of fighters needed to perform the same combat role." (U.S. News & World, 17 December 1990)

This then, became the formal ATF Specification.

1985 P&W fabricated the first YF119 engine components.

September 1985 The formal RFP was released by the Air Force SPO to industry. The only change to the above 1984 specification was a reduction in unit cost cap to $35 million. The final submission date was stipulated to be January 1986, later relaxed to April. At this stage, there no plans for actual prototypes, the decision would be based on wind tunnel models and simulations.

November 1985 The Air Force SPO issued more stringent stealth goals.

1986 Tests of non-flightworthy engines took place: "The PW XF119 and GE XF120 prototype engines ran in time for lessons learned to be incorporated into the flying YF119 and YF120 versions for the PAVs"

March 1986 US Navy entered the programme, agreeing to use the ATF as a basis for replacement for the F-14 Tomcat. In exchange, the AF would find an F-111 replacement based on the Navy's Advanced Tactical Aircraft (ATA) program.

May 1986 A major change was made. The Secretary of the Air Force, Edward Aldridge, announced that the AF would now order actual flying prototypes of 2 competing ATF designs. The ATF Dem/Val would now include prototype aircraft, engines, and prototype avionics demonstration. This was in response to the Packard Commission that was convened in 1984 to review the Pentagon's procurement practises. David Packard had been strongly in favour of 'fly before buy'. In relation to Low Observability, ordering actual flying prototpyes would allow this aspect to be pushed alot harder because unconventional configurations could developed that would otherwise be risky if only tested in reduced scale model form.

Jay Miller in his Aerofax F-22 book explains further: "Edward Aldridge announced the AF had decided not to make its final ATF choice from the paper studies made under the original Demonstation/Validation concept, but rather to expand Dem/Val to include a prototype fly-off that would pit the aircraft of the 2 most promising designs against each other. Each contender was to build 2 prototypes, each to be powered by examples of the 2 contending engine manufacturers. Dem/Val would now include best-effort flying prototypes and avionics protoypes. Only 2 contracts would be selected, teaming would be encouraged, cost proposals would be requested, and they would be asked how they would tailor the remainder of the Dem/Val effort to optimize risk reduction within available budget. This was to permit a more accurate asessment of capabilities in the critical areas of LO technology and basic performance. The prototypes would NOT be intended for a DIRECT competitive fly-off, or to demonstrate ability with every performance requirement, but rather to demonstrate that each company's concept was fundamentally viable. Contractors would have open flexibility in determining their respective flight test plans."

Herein lies the essence of the competition and how the aircraft were evaluated. The Air Force placed emphasis on choosing between 2 sets of projections of what the FSD would be like. The prototypes were to be used simply to support those projections. It was the company FSD projections that were competing directly, not the prototype aircraft.

June 1986 Contracts were awarded to P&W and GE for flight worthy prototype engines. These were designated YF119-PW-100 and YF120-GE-100 respectively by the Air Force SPO.

28 July 1986 six remaining airframe contenders submitted their prototype designs.

August 1986 In European style, 2 teams were announced as the companies realised the cost of developing this aircraft would be well beyond what what any single company could afford. Lockheed, Boeing, and GD signed an MoU leading to a team agreement. Northrop announced it would team with McDDC; whichever company won would lead the effort.

September 1986 Assembly began on the first YF119-PW-100 engine, testing began in October.

31 October 1986 The Secretary of the Air Force announced that Lockheed and Northrop's designs were selected as the final contenders for the Demonstration/Validation stage, each receiving a $691 million contract. General Dynamics came 2nd, Boeing had scored 3rd, McDonnell Douglas 4th, with Grumman and Rockwell coming last. Piccirillo stated "We had two excellent designs and three good designs, and two where the designers hadn't quite got the idea." Lockheed's proposal was officially named YF-22 by the AF. Northrop's proposal was the model N-14, named YF-23 by the AF. $100 million was allocated to radar and electro optical sensors, and $200 million for avionics architecture. An additional $650 million was awarded to each engine company. Northrop and McDonnell Douglas called their partnership the 'ATF-23 Team'.

The Dem/Val phase was to be a comprehensive 4 year programme split into several sectors: Avionics, Radar Cross Section (RCS) prediction, flying qualities, serviceability, and programme management. It had 3 formal categories:

1) System Specification Development (SSD), which employed effectiveness analysis, design trade-off analysis, technology evaluations, and simulation to refine operational requirements. SSD covered development and test of new airframe materials, combat simulation exercises, and demonstration of maintenance techniques. It also included RCS testing and analysis on full scale and subscale models, components, and digital RCS prediction models. The full scale models that were built had to include all radar reflective features and absorbing materials envisaged for the actual protoypes. The full scale models were mounted on a 70ft pole at the RATSCAT facility at White Sands New Mexico. Test pilot Paul Metz described the SSD as "minimising the unknowns and 'I forgots' that have driven FSD costs out of the roof in the past."

3) Prototype Air Vehicles (PAV), which were used to demonstrate the capabilites on which the Full Scale Development (FSD) proposals would be based. Each team had to build 2 prototypes (known as PAV-1 and -2) one each powered by examples of the GE and P&W engines, resulting in 4 different combinations. The PAV segment was not a flyoff in the traditional sense. The purpose was to allow the USAF to verify predicted FSD aircraft and engine performance against actual demonstrated PAV performance. It was not a comparison of flight perfomance, but a comparison of the teams' abilities to predict accurately in terms of their respective FSD proposals. The emphasis was on validation. To this end, the teams were given a certain amount of freedom to choose the main technological emphases of their PAV programs. Most important was to demonstrate that a stealthy aircraft could be an agile fighter, and that speed, stealth, and agility could all be combined into one aircraft.

In a break from tradition, the contractors had overall responsibility for planning and execution of the flight test programmes rather than the Air Force Flight Test Center directly. The capabilites to be demonstrated were left to the discretion of the teams. The only guidelines stipulated was that the prototype should be flown for the purpose of FSD risk reduction.

1987 Brigadier General James A Fain became the new ATF Program Director.

13 July 1987 Lockheed determined that its design was technically and competitively unacceptable, so it requested a 6 month extension to the rollout deadline in order to make the necessary changes. A new design initiative was instated and following a very intense 3 month effort, a new configuration was developed. Northrop was fundmentally happy with its design and no major revisions were made.

April 1988 Lockheed 'unfroze' its design again to attempt further reduction in supersonic drag.

May 1988 The first overall ATF Acquisition Programme Baseline was prepared.

18 August 1989 The draft RFP calling for Full Scale Development (FSD, later renamed to Engineering Manufacturing and Development EMD) was released.

December 1988 The USAF SPO announced that the runway distance requirement necessitating thrust reversal would be dropped, in response to the results of the F-15B S/MTD programme. This was too late to affect the configuration of the PAV engines and the aircraft prototypes would fly with engines to the original design.

27 August 1990 The flight test portion of the Dem/Val phase commenced with the first flight of an ATF: the Northrop YF-23 PAV-1, piloted by Paul Metz.

1 November 1990 The EMD RFP was issued.

18 December 1990 The last flight of Northrop's flight test programme is completed using PAV-2.

31 December 1990 Company EMD Proposals were delivered to the USAF SPO. "A manufacturing team led by Lockheed, maker of the YF-22, and another headed by Northrop, maker of the YF-23, have each submitted 15,000 pages of data to the Air Force in an effort to convince officials that each company's model is the best candidate to replace the F-15 Eagle". (Time Magazine 18 March 1991, 'Dogfight Over The Pentagon', by Philip Elmer-Dewitt)

23 April 1991 The USAF announces its final decision as to which team would go ahead to the EMD Phase.