Known by Helio as the model H-500 this STOL aircraft mounted twin Lycoming engines on top of the high-set wing, close to the fuselage.

[1] With the engines mounted in this manner, lateral and over-the-nose visibility were much improved while the propellers were kept clear of cabin doors and away from possible debris damage during rough field operations.

This was a tail-wheel design, so the vertical component of propeller thrust assisted STOL take-off performance from rough fields.

In 1967 or 68, work was started on a redesign of the Twin Courier in a tricycle-gear configuration for the commercial market, since many firms which desired STOL capability had regulations which required multi-engine aircraft.

[3] (The Twin Courier met FAA requirements marginally and was certificated to meet immediate needs for service in Vietnam, on the understanding that the design would not be marketed commercially.