Fairchild Republic A-10 Thunderbolt II – Warthog

The Fairchild Republic A-10 Thunderbolt II is a single-seat, twin turbofan engine, straight wing jet aircraft developed by Fairchild-Republic for the United States Air Force. The A-10 was designed around the 30 mm GAU-8 Avenger rotary cannon. Its airframe was designed for durability, with measures such as 540 kg of titanium armour to protect the cockpit and aircraft systems, enabling it to absorb a significant amount of damage and continue flying. Its short take-off and landing capability permit operation from airstrips close to the front lines, and its simple design enables maintenance with minimal facilities.

Post-World War II development of conventionally armed attack aircraft in the United States had stagnated. Design efforts for tactical aircraft focused on the delivery of nuclear weapons using high-speed designs like the F-101 Voodoo and F-105 Thunderchief. Designs concentrating on conventional weapons had been largely ignored, leaving their entry into the Vietnam War led by the Korean War-era Douglas A-1 Skyraider. While a capable aircraft for its era, with a relatively large payload and long loiter time, the propeller-driven design was also relatively slow and vulnerable to ground fire, as well as having poor firepower. The U.S. Air Force and Marine Corps lost 266 A-1s in action in Vietnam, largely from small arms fire.

Douglas A-1 Skyraider

The lack of modern conventional attack capability prompted calls for a specialized attack aircraft. On 7 June 1961, Secretary of Defence McNamara ordered the USAF to develop two tactical aircraft, one for the long-range strike and interdictor role, and the other focusing on the fighter-bomber mission. The former became the Tactical Fighter Experimental, or TFX, which emerged as the F-111 Aardvark, while the second was filled by a version of the U.S. Navy's F-4 Phantom II. While the Phantom went on to be one of the most successful fighter designs of the 1960’s, and proved to be a capable fighter-bomber, its lack of over target time was a major problem, and to a lesser extent, its poor low-speed performance. It was also expensive to buy and operate, with a flyaway cost of $2 million in 1965 ($15.9 million today), and operational costs over $900 per hour ($7,000 per hour today).

F-4 Phantom II F-111 Aardvark

After a broad review of its tactical force structure, the U.S. Air Force decided to adopt a low-cost aircraft to supplement the F-4 and F-111. It first focused on the Northrop F-5, which had air-to-air capability. A 1965 cost-effectiveness study shifted the focus from the F-5 to the less expensive LTV A-7D, and a contract was awarded. However, this aircraft original cost doubled with demands for upgraded engine and new avionics.


During this period, the United States Army had been introducing the UH-1 Iroquois into service. First used in its intended role as a transport, it was soon modified in the field to carry more machine guns in what became known as the helicopter gunship role. This proved effective against the lightly armed enemy, and new gun and rocket pods were added. Soon the AH-1 Cobra was introduced. This was an attack helicopter armed with long-range BGM-71 TOW missiles able to destroy tanks from outside the range of defensive fire. The helicopter was effective and prompted the U.S. military to change its defensive strategy in Europe by blunting any Warsaw Pact advance with anti-tank helicopters instead of the tactical nuclear weapons that had been the basis for NATO's battle plans since the 1950's.

UH-1 Iroquois AH-1 Cobra

The Cobra was a quickly made helicopter based on the UH-1 Iroquois, though, and in the late 1960s the U.S. Army was designing the Lockheed AH-56 Cheyenne, a much more capable attack aircraft with greater speed. These developments worried the USAF, which saw the anti-tank helicopter overtaking its nuclear-armed tactical aircraft as the primary anti-armour force in Europe. A 1966 Air Force study of existing close air support capabilities revealed gaps in the escort and fire suppression roles, which the Cheyenne could fill. The study concluded that the service should acquire a simple, inexpensive, dedicated CAS aircraft at least as capable as the A-1, and that it should develop doctrine, tactics, and procedures for such aircraft to accomplish the missions for which the attack helicopters were provided.

Lockheed AH-56 Cheyenne

On 8 September 1966, General John P. McConnell, Chief of Staff of the USAF, ordered that a specialized CAS aircraft be designed, developed, and obtained. On 22 December, a Requirements Action Directive was issued for the A-X CAS airplane, and the Attack Experimental (A-X) program office was formed. On 6 March 1967, the Air Force released a request for information to 21 defence contractors for the A-X. The objective was to create a design study for a low-cost attack aircraft. In 1969, the Secretary of the Air Force asked Pierre Sprey to write the detailed specifications for the proposed A-X project; Sprey's initial involvement was kept secret due to his earlier controversial involvement in the F-X project.

Sprey's discussions with Skyraider pilots operating in Vietnam and analysis of aircraft used in the role indicated the ideal aircraft should have long over target time, low-speed manoeuvrability, massive cannon firepower, and extreme survivability; possessing the best elements of the Ilyushin Il-2, Henschel Hs 129, and Skyraider. The specifications also demanded that each aircraft cost less than $3 million (equivalent to $20.5 million today). Sprey required that the biography of World War II Luftwaffe attack pilot Hans-Ulrich Rudel be read by people on the A-X program.

Ilyushin Il-2 Henschel Hs 129

In May 1970, the USAF issued a modified, more detailed request for proposals for the aircraft. The threat of Soviet armoured forces and all-weather attack operations had become more serious. The requirements now included that the aircraft would be designed specifically around the 30 mm rotary cannon. The RFP also specified a maximum speed of 400 knts, take-off distance of 1,200 m, external load of 16,000 pounds, 285-mile mission radius, and a unit cost of US$1.4 million ($9 million today). The A-X would be the first USAF aircraft designed exclusively for close air support. During this time, a separate RFP was released for A-X's 30 mm cannon with requirements for a high rate of fire, 4000 round per minute, and a high muzzle velocity. Six companies submitted aircraft proposals, with Northrop and Fairchild Republic selected to build prototypes: the YA-9A and YA-10A, respectively. General Electric and Philco-Ford were selected to build and test GAU-8 cannon prototypes.

GAU-8 cannon

Two YA-10 prototypes were built in the Republic factory in Farmingdale, New York, and first flew on 10 May 1972 by pilot Howard "Sam" Nelson. Production A-10s were built by Fairchild in Hagerstown, Maryland. After trials and a fly-off against the YA-9, on 18 January 1973, the USAF announced the YA-10's selection for production. General Electric was selected to build the GAU-8 cannon in June 1973. The YA-10 had an additional fly-off in 1974 against the Ling-Temco-Vought A-7D Corsair II, the principal USAF attack aircraft at the time, to prove the need for a new attack aircraft. The first production A-10 flew in October 1975, and deliveries commenced in March 1976.

YA-9 YA-10

One experimental two-seat A-10 Night Adverse Weather (N/AW) version was built by converting an A-10A. The N/AW was developed by Fairchild from the first Demonstration Testing and Evaluation A-10 for consideration by the USAF. It included a second seat for a weapons system officer responsible for electronic countermeasures (ECM), navigation and target acquisition. The N/AW version did not interest the USAF or export customers. The two-seat trainer version was ordered by the Air Force in 1981, but funding was cancelled by U.S. Congress and the jet was not produced. The only two-seat A-10 built now resides at Edwards Air Force Base's Flight Test Centre Museum.

Two-seat A-10

On 10 February 1976, Deputy Secretary of Defence Bill Clements authorized full-rate production, with the first A-10 being accepted by the Air Force Tactical Air Command on 30 March 1976. Production continued and reached a peak rate of 13 aircraft per month. By 1984, 715 airplanes, including two prototypes and six development aircraft, had been delivered. When A-10 full-rate production was first authorized the aircraft's planned service life was 6,000 hours. A small reinforcement to the design was quickly adopted when the A-10 failed initial fatigue testing at 80% of testing; with the fix, the A-10 passed the fatigue tests. 8,000-flight-hour service lives were becoming common at the time, so fatigue testing of the A-10 continued with a new 8,000-hour target. This new target quickly discovered serious cracks at Wing Station 23 (WS23) where the outboard portions of the wings are joined to the fuselage. The first production change was to add cold working at WS23 to address this problem. Soon after, the Air Force determined that the real-world A-10 fleet fatigue was harsher than estimated, forcing them to change their fatigue testing and introduce "spectrum 3" equivalent flight-hour testing.

Spectrum 3 fatigue testing started in 1979. This round of testing quickly determined that more drastic reinforcement would be needed. The second change in production, starting with aircraft #442, was to increase the thickness of the lower skin on the outer wing panels. A tech order was issued to retrofit the "thick skin" to the whole fleet, but the tech order was rescinded after roughly 242 planes, leaving about 200 planes with the original "thin skin". Starting with aircraft #530, cold working at WS0 was performed, and this retrofit was performed on earlier aircraft. A fourth, even more drastic change was initiated with aircraft #582, again to address the problems discovered with spectrum 3 testing. This change increased the thickness on the lower skin on the canter wing panel, but it required modifications to the lower spar caps to accommodate the thicker skin. The Air Force determined that it was not economically feasible to retrofit earlier planes with this modification.

The A-10 has received many upgrades since entering service. In 1978, the A-10 received the Pave Penny laser receiver pod, which receives reflected laser radiation from laser designators to allow the aircraft to deliver laser guided munitions. The Pave Penny pod is carried on a pylon mounted below the right side of the cockpit and has a clear view of the ground. In 1980, the A-10 began receiving an inertial navigation system. In the early 1990s, the A-10 began to receive the Low-Altitude Safety and Targeting Enhancement (LASTE) upgrade, which provided computerized weapon-aiming equipment, an autopilot, and a ground-collision warning system. In 1999, aircraft began receiving Global Positioning System navigation systems and a multi-function display. The LASTE system was upgraded with Integrated Flight & Fire Control Computers (IFFCC). Proposed further upgrades included integrated combat search and rescue locator systems and improved early warning and anti-jam self-protection systems, and the Air Force recognized that the A-10's engine power was sub-optimal and had been planning to replace them with more powerful engines since at least 2001 at an estimated cost of $2 billion.

In 1987, Grumman Aerospace took over support for the A-10 program. In 1993, Grumman updated the damage tolerance assessment and Force Structural Maintenance Plan and Damage Threat Assessment. Over the next few years, problems with wing structure fatigue, first noticed in production years earlier, began to come to the fore. The process of implementing the maintenance plan was greatly delayed by the base realignment and closure commission (BRAC), which led to 80% of the original workforce being let go.

During inspections in 1995 and 1996, cracks at the WS23 location were found on many aircraft, most of them in line with updated predictions from 1993. However, two of these were classified as "near-critical" size, well beyond predictions. In August 1998, Grumman produced a new plan to address these issues and increase life span to 16,000 hours. This resulted in the "HOG UP" program, which commenced in 1999. Over time, additional aspects were added to HOG UP, including new fuel bladders, changes to the flight control system, and inspections of the engine nacelles. In 2001, the cracks were reclassified as "critical", which meant they were considered repairs and not upgrades, which allowed bypassing normal acquisition channels for more rapid implementation.

An independent review of the HOG UP program at this point concluded that the data on which the wing upgrade relied could no longer be trusted. This independent review was presented in September 2003. Shortly thereafter, fatigue testing on a test wing failed prematurely and also mounting problems with wings failing in-service inspections at an increasing rate became apparent. The Air Force estimated that they would run out of wings by 2011. Of the plans explored, replacing the wings with new ones was the least expensive, with an initial cost of $741 million, and a total cost of $1.72 billion over the life of the program.

In 2005, a business case was developed with three options to extend the life of the fleet. The first two options involved expanding the service life extension program (SLEP) at a cost of $4.6 billion and $3.16 billion, respectively. The third option, worth $1.72 billion, was to build 242 new wings and avoid the cost of expanding the SLEP. In 2006, option 3 was chosen and Boeing won the contract. The base contract is for 117 wings with options for 125 additional wings. In 2013, the Air Force exercised a portion of the option to add 56 wings, putting 173 wings on order with options remaining for 69 additional wings. In November 2011, two A-10s flew with the new wings fitted. The new wings improved mission readiness, decreased maintenance costs, and allowed the A-10 to be operated up to 2035 if necessary. The re-winging effort was organized under the thick-skin urgent spares kitting program.

In 2014, as part of plans to retire the A-10, the USAF considered halting the wing replacement program to save an additional $500 million; however, by May 2015 the re-winging program was too far into the contract to be financially efficient to cancel. Boeing stated in February 2016 that the A-10 fleet with the new TUSK wings could operate to 2040.

In 2005, the entire fleet of 356 A-10 and OA-10 aircraft began receiving the Precision Engagement upgrades including an improved fire control system (FCS), electronic countermeasures (ECM), and smart bomb targeting. The aircraft receiving this upgrade were re-designated A-10C. The Government Accounting Office in 2007 estimated the cost of upgrading, refurbishing, and service life extension plans for the A-10 force to total $2.25 billion through 2013. In July 2010, the USAF issued Raytheon a contract to integrate a Helmet Mounted Integrated Targeting (HMIT) system into the A-10C. The Air Force Material Command's Ogden Air Logistics Centre at Hill AFB, Utah completed work on its 100th A-10 precision engagement upgrade in January 2008. The final aircraft was upgraded to A-10C configuration in June 2011. The aircraft also received all-weather combat capability, and a Hand-on-Throttle-and-Stick configuration mixing the F-16's flight stick with the F-15's throttle. Other changes included two multifunction displays, a modern communications suite including a Link-16 radio and SATCOM. The LASTE system was replaced with the integrated flight and fire control computer (IFFCC) included in the PE upgrade.

Throughout its life, the platform's software has been upgraded several times, and although these upgrades were due to be stopped as part of plans to retire the A-10 in February 2014, Secretary of the Air Force Deborah Lee James ordered that the latest upgrade, designated Suite 8, continue in response to Congressional pressure. Suite 8 software includes IFF Mode 5, which modernizes the ability to identify the A-10 to friendly units. Additionally, the Pave Penny pods and pylons are being removed as their receive-only capability has been replaced by the AN/AAQ-28(V)4 LITENING AT targeting pods or Sniper XR targeting pod, which both have laser designators and laser rangefinders.

In 2012, Air Combat Command requested the testing of a 2,300 l external fuel tank which would extend the A-10's over target time by 45–60 minutes; flight testing of such a tank had been conducted in 1997, but did not involve combat evaluation. Over 30 flight tests were conducted by the 40th Flight Test Squadron to gather data on the aircraft's handling characteristics and performance across different load configurations. It was reported that the tank slightly reduced stability in the yaw axis, but there was no decrease in aircraft tracking performance.

The future of the platform remains the subject of debate. In 2007, the USAF expected the A-10 to remain in service until 2028 and possibly later, when it would likely be replaced by the Lockheed Martin F-35 Lightning II. However, critics have said that replacing the A-10 with the F-35 would be a "giant leap backwards" given the A-10's performance and the F-35's high costs. In 2012, the Air Force considered the F-35B STOVL variant as a replacement CAS aircraft, but concluded that the aircraft could not generate sufficient sorties. In August 2013, Congress and the Air Force examined various proposals, including the F-35 and the MQ-9 Reaper unmanned aerial vehicle filling the A-10's role. Proponents state that the A-10's armour and cannon are superior to aircraft such as the F-35 for ground attack, that guided munitions other planes rely upon could be jammed, and that ground commanders frequently request A-10 support.

In the USAF's 2015 budget, the service considered retiring the A-10 and other single-mission aircraft, prioritizing multi-mission aircraft; cutting a whole fleet and its infrastructure was seen as the only method for major savings. The U.S. Army had expressed interest in obtaining some A-10s should the Air Force retire them, but later stated there was "no chance" of that happening. The U.S. Air Force stated that retirement would save $3.7 billion from 2015 to 2019. The prevalence of guided munitions allows more aircraft to perform the CAS mission and reduces the requirement for specialized aircraft; since 2001 multirole aircraft and bombers have performed 80 percent of operational CAS missions. The Air Force also said that the A-10 was more vulnerable to advanced anti-aircraft defences, but the Army replied that the A-10 had proved invaluable because of its versatile weapons loads, psychological impact, and limited logistics needs on ground support systems.

In January 2015, USAF officials told lawmakers that it would take 15 years to fully develop a new attack aircraft to replace the A-10; that year General Herbert J. Carlisle, the head of Air Combat Command, stated that a follow-on weapon system for the A-10 may need to be developed. It planned for F-16s and F-15Es to initially take up CAS sorties, and later by the F-35A once sufficient numbers become operationally available over the next decade. In July 2015, Boeing held initial discussions on the prospects of selling retired or stored A-10s in near-flyaway condition to international customers. However, the Air Force then said that it would not permit the aircraft to be sold.

Plans to develop a replacement aircraft were announced by the US Air Combat Command in August 2015. Early the following year, the Air Force began studying future CAS aircraft to succeed the A-10 in low-intensity "permissive conflicts" like counterterrorism and regional stability operations, admitting that the F-35 would be too expensive to operate in day-to-day roles. A wide range of platforms were under consideration, including everything from low-end AT-6 Wolverine and A-29 Super Tucano turboprops and the Textron AirLand Scorpion as more basic off-the-shelf options to more sophisticated clean-sheet attack aircraft or "AT-X" derivatives of the T-X next-generation trainer as entirely new attack platforms.


AT-6 Wolverine A-29 Super Tucano

In January 2016, the USAF was "indefinitely freezing" plans to retire the A-10 for at least several years. In addition to Congressional opposition, its use in anti-ISIL operations, deployments to Eastern Europe as a response to Russia's military intervention in Ukraine, and revaluation of F-35 numbers necessitated its retention. In February 2016, the Air Force deferred the final retirement of the aircraft until 2022 after being replaced by F-35s on a squadron-by-squadron basis. In October 2016, the Air Force Material Command brought the depot maintenance line back to full capacity in preparation for re-winging the fleet. In June 2017 it was announced that the aircraft "...will now be kept in the air force’s inventory indefinitely."

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