The first Heron, Series 1A suffered deficiencies, as NAC soon discovered. First, the aircraft was generally underpowered. Its quite heavy engines (weighing about each), had an output of only each. By comparison, later modifications or rebuilt aircraft had as much as 50% more power (in the case of the Saunders ST-27). Unlike the Dove, the Heron came with a fixed undercarriage and no nosewheel steering, which simplified maintenance, but reduced top speed. Secondly the lightweight aluminium alloy wingspars were prone to constant cracking due to the heavy loading on the wing caused by the overweight engines and rough landings on unpaved runways at the time. NAC resolved this by replacing the aluminium spars with heavier steel spars, reducing the performance of the Heron Series 1A (re-classified 1B) to uneconomic levels for the services required of them in New Zealand. NAC disposed of them in 1957.