Helio Stallion

The Helio HST-550 Stallion was an STOL utility aircraft developed in the United States in 1963. The prototype flew in July 1964. Initially conceived as a turboprop-powered variant of the Helio Courier, it eventually emerged as a completely new design of the same general configuration and much of its design was initiated from components used in the Helio H-500 Twin. It was a much larger aircraft than the Courier, and Helio soon discovered that it was too expensive for the market.

The USAF however, emerged as a buyer for the design, purchasing the aircraft for the Credible Chase programme as the AU-24A. This was the gunship version of the Stallion, with a PT6A-27 680 shp (510 kW) turboprop, equipped with a General Electric XM-197 three-barrel 20 mm Gatling gun mounted in the left cargo door. It also had five underwing and fuselage hardpoints.

Of the 18 aircraft purchased, fourteen or fifteen were eventually sold to the Khmer Air Force.

Helio Stallion
Class Aircraft
Type Utility
Manufacturer Helio Aircraft Company
Origin United States of America
Country Name Origin Year
United States of America 1964
Country Name Operational Year Retirement Year
United States of America View
ManufacturerName Production From Production To Quantity
Helio Aircraft Company 20 View


  •     H-550 - prototypes (2 built)
  •         AU-24A (H-550A) - production version (18 built)
  •     H-634 Twin Stallion - version with twin Allison 250 turboprops mounted on a beam across the nose of the aircraft (not built)
  •     H-1201T Twin Stallion - version with twin engines in underwing nacelles, retractable undercarriage, tiptanks, and underwing cargo pods (not built)

Role Civil utility aircraft
National origin United States
Manufacturer Helio
First flight 5 June 1964
Primary user USAF/CIA
Number built 20

General characteristics

  • Crew: One pilot
  • Capacity: 9 passengers
  • Length: 39 ft 7 in (12.07 m)
  • Wingspan: 41 ft 0 in (12.50 m)
  • Height: 9 ft 3 in (2.81 m)
  • Wing area: 242 ft2 (22.48 m2)
  • Empty weight: 2,860 lb (1,287 kg)
  • Gross weight: 5,100 lb (2,313 kg)
  • Powerplant: 1 × Pratt & Whitney Canada PT6A-27, 680 hp (507 kW)


  • Maximum speed: 216 mph (348 km/h)
  • Cruise speed: 160 mph (257 km/h)
  • Range: 641 miles (1,031 km)
  • Service ceiling: 25,000 ft (7,620 m)
  • Rate of climb: 2,200 ft/min (11 m/s)

End notes