History:

To meet customer requirement, Transavia continued with further development of the basic Airtruk, and this led to the Model T-320 Airtruk fitted with the Rolls Royce/Continental Tiara 6-320-2B engine producing 239 kw (320 hp).  Production of this model began in October 1976, and several were assembled in New Zealand by Flight Engineering Ltd but, after eighteen months, production of this engine ceased. Transavia then selected the Lycoming IO-540 series engine of 224 kw (300 hp) as a replacement.  Fitted with the IO-540-K1A5 engine, the new model became known as the T-300 Skyfarmer, this model being certified in Australia for a max take-off weight in the agricultural role of 1,925 kg (4,244 lb), lifting 953 kg (2,101 lb) but in some parts of the world lifting 1,179 kg (2,599 lb).

The basic airframe was stressed to +3.8 and –2 G, and was built around a one-tonne capacity hopper.  It could spread up to a 30 m (98 ft 5 in) swathe of liquid or solid payload, and could deliver up to 450 litres (90 Imp gal) per minute in the spraying role.  Transavia’s Powermist system only absorbed two percent of the power available.  The Skyfarmer had an empty weight of 907 kg (2,000 lb), a loaded weight of 1,855 kg (4,090 lb) and a maximum speed of 206 km/h (128 mph).

In June 1981 the improved Skyfarmer T-300A was flown and displayed at the Paris Air Show.  Significant changes included expansion of the cabin structure to provide a larger, roomier cockpit and hopper throat, new aerodynamically balanced ailerons, horn balanced elevators, and electro-mechanical flaps to reduce the workload of the pilot.

The T-400A SkyFarmer was developed by Transavia as a trainer for China, production of this model commencing in early 1986.  The first mock-up of this model was based on the prototype utility aircraft VH-TRM (c/n 1043). Four were purchased by the Australian Government following Australian certification on 23 December 1985, a new certificate of airworthiness over the T-300 being required because of the marked alterations to the design.  These four aircraft were donated under the Australian Aid Programme to China and were used to train crews in agricultural operations, instructors being trained at Cudal, NSW.

The prototype T-400 was badly damaged during the conversion course following a heavy landing and had to be rebuilt.  The mock-up of the two-seat trainer was built and went to the Heilongjiang Province in south-east China.  At that time plans were being considered to build the SkyFarmer in China.  The T-400 first flew in September 1984 with a 224 kw (300 hp) IO-540-K1A5 engine with a Hartzell three-blade propeller.

Production aircraft of the T-400 series had a 50% larger stub-wing, a 298 kw (400 hp) Lycoming IO-720-DIBD engine, a new Hartzell propeller, a 76.2 cm (30 in) extension to the booms to improve effectiveness of the control surfaces, and carried an extra 299 kg (660 lb) load. It also had electric flaps and trimmer and a re-designed undercarriage.

Continued development of the design led to the PL-12 MIL (for military), a model aimed at the military market for a light utility aircraft , this being a development of the utility PL-12U which was built for civil operation as a utility transport, air ambulance and aerial survey aircraft, but using the larger fuselage of the T-400 series.  It was also proposed to be used for forward air control, light attack and counter insurgency. It was also known as the M-300. A further proposed variant was the PL-12 550T fitted with a Pratt & Whitney PT6A turboprop.

The background to the development of this aircraft is a little vague now but it is believed at some stage the airframe was damaged by fire. It was built to meet a requirement of the Philippines Government to build a spray variant which could be used in the medevac role and which could be fitted, if required, with four or six machine guns for operations against mountain tribesmen.  In the event Transavia decided against tendering for the contract and the aircraft was not completed but was painted in a medevac colour scheme.

Only this mock-up of the PL-12 MIL (also known as the PL-12U) was completed and was placed on display at the Australian Bicentennial Airshow at RAAF Richmond, NSW in October 1988.  This aircraft was made up of parts available at the end of production at Seven Hills, NSW using parts left over from the production line and parts from other aircraft which were no longer airworthy.  It was subsequently placed in storage and later donated to and placed on display at the Australian Aviation Museum at Bankstown, NSW. It is not known at present what its fate is following the closure of the museum in 2019.