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AU-23 Fairchild Peacemaker

Fairchild AU-23 PeacemakerTThe AU-23 is an all-metal, light-weight, high-wing monoplane manufactured by Fairchild Industries. It has a rectangular, strut-braced wing of constant profile over the entire span. The wing has four mechanically and interconnected inboard and outboard double-slotted, electrically operated flaps. The aircraft has a fixed, conventional landing gear. The pitch axis is controlled by a conventional elevator with electrical and manual trim. Aileron trim is electric and rudder trim is manual. The AU-23A is powered by an Airesearch Model TPE331-1-101 turboprop engine, flat-rated at 650 shaft horsepower (shp). The engine is equipped with a 3-bladed, constant-speed, full-feathering Hartzell propeller that has beta and reverse ranges. The aircraft has five ordnance stations, four wing pylons, and a fuselage pylon. The aft cabin is configured to mount the XM-197 20-mm automatic gun system. Maximum gross weight of the aircraft is 6,100 pounds.

The idea of using a light STOL mini-gunship to provide niche capabilities had been tried before in Southeast Asia. The mini-gunship had been previously tested in Thailand under the Pave Coin program. Initial combat test results from the Pave Coin program had been encouraging, and while the idea of incorporating them into Vietnamization was new, the positive initial results of testing in Thailand made the Credible Chase program an easier sell to Congress.

In May 1971 the Aeronautical Systems Division at Wright-Patterson Air Force Base, Ohio, began work on a project to evaluate the potential use of armed light utility short takeoff and landing aircraft in Southeast Asia. The program, named Credible Chase, was designed to add mobility and firepower to the South Vietnamese Air Forces in a relatively short time. Two commercial aircraft were selected for testing: the Fairchild Porter and the Helio Stallion. Initial performance testing was conducted with leased aircraft at Eglin Air Force Base, Fla., and was successful enough to warrant a combat evaluation. The Porter, designated AU-23A, was fitted with a side-firing 20mm XM-197 Gatling cannon, four wing pylons and a center fuselage station for external ordnance. The 20mm cannon was essentially a three barrel version of the M61 "Vulcan" 6-barrel 20mm cannon. The aircraft could carry a variety of ordnance including forward firing gun pods, 500 and 250 pound bombs, napalm units, cluster bomb units, flares, rockets, smoke grenades and propaganda leaflet dispensers.

The combat evaluation of PAVE COIN, was done in June and July 1971. The AU-23A was tested for eight possible missions: armed escort of helicopters, close air support, hamlet defense, STOL airlift and resupply, armed reconnaissance, border surveillance, forward air control, and counter infiltration. USAF crews flew 73 missions (94 sorties) and RVNAF crews flew 68 missions (85 sorties). Several types of weapons were test dropped/fired including 2.75 inch rockets (explosive and smoke), cluster bomb units (CBU-14), MK 6 Mod 3 flares, and MK 81, 82 and 106 practice bombs. More than 8,000 rounds of 20mm ammunition was also fired, including both high explosive incendiary and target practice tracer types. Several problems were discovered during the PAVE COIN program, the most serious was the extreme vulnerability of the aircraft to all but the lightest antiaircraft fire (below 12.7mm).

In May 1971, the SECDEF tasked the SECAF to evaluate the concept of using light off-the-shelf Short Takeoff and Landing (STOL) mini-gunship aircraft in a counter infiltration role to fill this capability gap. The solution proposed by DDR&E recommended the purchase of STOL mini-gunships to alleviate this shortfall. A smaller, less-complicated mini-gunship would fill the RVNAF capability gap with a minimum investment in manpower logistics and training. The time of need for the mini-gunship program, however, was extremely short as the SECDEF directed the Air Force to combat test it the following dry season (early 1972).

Convincing Congress of the utility of the program was a crucial step its development. Congress held the purse strings for the defense budget and its support was required to secure rapid funding for Credible Chase so it could meet program deadlines. The initial request to Congress for the procurement of 30 aircraft (15 AU-23 Fairchild Peacemakers and 15 AU-24 Helio Stallions) was submitted initially as an amendment to the fiscal year (FY) 1972 budget. Due to the urgency of the project, the funding request was moved up, and the DoD instead approached Congress with a requested reprogramming of 1971 funds to cover the cost of Credible Chase.

The purchase of 30 aircraft instead of the traditional two or three typically procured for testing was unprecedented, but would enable 24-hour, seven-days-perweek operations for evaluating the concept in South Vietnam. The generals argued even if the concept were not to prove entirely successful, these airplanes could still be used by the Vietnamese in a close air support and hamlet defense role. Gen. Fish also explained that the need for urgency was being driven by environmental factors in Vietnam. The Vietnamese dry season was the only permissible time to conduct an operational test of the Credible Chase concept due to the limitations that adverse weather would have upon aircraft operations. The 30 aircraft had to be ready for fielding in the spring of 1972, to run the test, and if successful, get a capability built by the following dry season at the end of calendar 1972.

Despite the problems, the USAF continued with the development program and ordered 15 AU-23As for further testing. Initial delivery of the AU-23 was delayed due to structural failure of the stabilator, causing a week-long delay in the delivery of the first aircraft. The initial cockpit layout was also problematic as the System Program Office did not allow for a Cockpit Configuration Control Board meeting prior to aircraft delivery. The result was that in the aircraft delivered the flap handle could not be reached with the throttle advanced, and the jettison button could be inadvertently activated. While these problems did not preclude the crews from flying the aircraft, they demonstrated a source of avoidable maintenance delays that negatively affected timely training.

The 4400th Special Operations Squadron (Provisional) was created to complete the operational test and evaluation of the Credible Chase aircraft. The first AU-23A (72-1306) was delivered to the 4400th SOS on Jan. 2, 1972, followed by two more aircraft (72-1304 & 72-1305) at the end of the month. Testing continued until Feb. 4, when the three aircraft were grounded because of cracks in the rudder assemblies. The first three aircraft were returned to Fairchild for repair and delivery of new aircraft resumed in late April 1972. On May 10, 1972, an AU-23A (S/N 72-1309) crashed after an in-flight engine failure. The pilot was not hurt, but all AU-23As were grounded until May 22, during the accident investigation. The last AU-23A was delivered on June 7 and testing was completed on June 28.

The 4400th recommended the aircraft not be used in combat without a major upgrade program. Specific problems identified included a slow combat speed (135 knots), a low working altitude, no capability for "zoom" escapes after delivering ordnance and a complete lack of armor protection for the crew and vital aircraft systems.

According to the test results, the operation of AU-23A in combat conditions was not recommended. Among the shortcomings called the low speed and altitude of the flight vulnerability from fire from the ground, the impossibility of a sharp climb after a load is relieved.

Fairchild Industries ran late in delivering the required number of Peacemakers, so that, well before the test could begin, enemy troops, massing for the March 1972 invasion, dominated the area near Pleiku chosen for the combat evaluation. The tactical situation in South Vietnam and southern Laos combined with the withdrawal of U.S. manpower to force the transfer of all tests to Eglin Air Force Base.

On June 30, 1972, 4400 SOS deposited its AU-23A in storage at Davis-Monthan AFB. Somewhat later, as part of the military assistance program, they were handed over to Thailand where they were used to guard the border.

Serial numbers 72-1304 to 72-1318
With weapons pylons and the minigun installed, the AU-23A was nicknamed "Credible Chase"
Wing span, m15.14 / 49 ft. 8 in.
Length of aircraft, m11.23 / 36 ft. 10 in.
Aircraft height, m3.73 / 14 ft. 4 in.
Wing area, m228.80
Weight, kg
empty aircraft1260
maximum take-off2767 / 6,100 lbs. maximum gross
Domestic fuel, l480.75
engine's type1 TBD Garrett TPE331-1-101F
power, kWt1 x 485 / 650 hp
Maximum speed, km / h280 / 148 knots at take-off power, 5,000 feet altitude, 6,000 lbs. gross weight
Cruising speed, km / h262 / 142 knots at maximum continuous power
Combat cruise speed 129 knots
Battle radius of action, km898 / 162 to 201 nautical miles depending on mission
Range 420 nautical miles
Endurance 4.84 hours
Maximum climb rate, m / min457
Practical ceiling, m6950
Crew, peopleThree (pilot, co-pilot, gunner)
Payload In transport configuration, the aircraft could carry six passengers or five troops with field gear or one litter patient, three ambulatory patients and one medical attendant
  • One XM-197 20mm side-firing cannon, plus up to 1925 lbs. of external stores on five pylons -- two on each wing (1400 lbs. of stores maximum) and a center fuselage pylon (525 lbs. of stores maximum).
  • In combat evaluations, the maximum ordnance load was about 1300 lbs.
  • The aircraft was also evaluated with side-firing XM 93 7.62mm minigun, XM 59 .50-cal. machine gun and XMU-470 20mm fixed side-firing gun pods.
  • Ordnance tested included SUU-11 gun pods, 2.75 inch rocket pods, BDU 33 with 25 lbs. bomblets, MK 81 250 lbs. bombs, MK 82 500 lbs. bombs, BLU-118 500 lbs. napalm canister, CBU-55 500 lbs. cluster bomb unit, MK-24 flares, ADU-272 canisters, smoke grenades and propaganda leaflet dispensers.

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    Page last modified: 07-09-2018 07:20:45 ZULU