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Summary

Summary

The helicopter was dropping incendiary bombs, from 100 feet above ground level, as part of a controlled bush burn. Prior to takeoff the pilot had placed his flying jacket between the rear of the pilot's seat and the incendiary delivery machine. During an incendiary dispatch run the exit chute became detached from the incendiary machine body allowing ignited bombs to fall inside the aircraft. One of these bombs set fire to the pilots jacket and this along, with the burning incendiaries, filled the cabin with dense black smoke. Despite the fact that the passengers opened their doors the dense smoke prevented the pilot from seeing anything either inside or outside the helicopter. He elected to land the aircraft immediately so the crew could extinguish the fire. During the unsighted landing in dense scrub the helicopter collided with a number of trees. It was reported that the clamp attaching the exit chute to the machine body had been secured normally prior to departure. The clamp design relied on friction only, to keep the chute in place. It is probable that natural helicopter vibration was sufficient to overcome the friction allowing the chute to separate. Once the chute separted, ignited incendiary balls were free to roll around inside the aircraft and set fire to the jacket. The design of the incendiary machine did not include any means of restricting the movement of the incendiary balls should they fall out of the machine. It was believed that the balls, which were only armed after they had entered the delivery system, could not escape. For the same reasons it was not believed that flammable material might be in danger if it was stored near the machine and consequently there were no restrictions and no placards prohibiting such storage. Safety Action Immediately following the accident the Bureau of Air Safety Investigation advised the owner of the incendiary equipment that the following modifications would improve the safety of the system. 1. A clearly visiable placard should be fitted to the incindiary machine indicating that objects should not be stored in its vicinity. 2. The chute attachment should be redisigned to make it more positive. 3. A fail safe system be designed to catch loose incindiaries. It is suggested that a metal tray, with sides, located under the dispensing machine would probably meet all requirements. The operator withdrew all similar incendery despensing devices from operations until the defects had been corrected. Redesign and modification of the devices has been completed and the machines have been returned to service.
 
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