On 11 July 1932, the prototype was dispatched to RAF Martlesham Heath for testing; it received its certificate of airworthiness during the following month. Flight testing had revelated the aircraft to possess relatively few flaws, any teething problems that did present themselves were quickly overcome. It was noted by pilots to handle well and be easy to fly. Due to vibration from the engines, there were instances of fuel tanks splitting and bracing wires snapping; it was addressed by installing rubber mounts for the oil tanks and replacing the wire with steel tubing. One relatively minor criticism, but still within acceptable margins, was the occasional instance of rudder overcorrection and oscillation; this was improved via the addition of what Armstrong Whitworth claimed to be the world's first spring tab.