What happened
On April 3, 2022, an Agusta Model AW13 and0, registration JA10TE, operated by the Iwate Prefectural Disaster Prevention Aviation Corps, was engaged in forest firefighting operations in Iwaizumi Town, Iwate Prefecture. After several rounds of water drops using various methods, the helicopter returned to the fire area following a period of refueling and equipment repositioning.
At approximately 15:31 JST, the crew performed a water drop using an external firefighting bucket. During this maneuver, the released water struck a volunteer firefighter on the ground, causing serious injuries, including fractures to the thoracic and lumbar regions. The individual was working on a nearby slope, attempting to extinguish smoldering trees, and was unable to evacuate the area before the impact occurred.
The investigation
The Japan Transport Safety Board (JTSB) examined the flight history recorded on the Multi-Purpose Flight Recorder (MPFR) and interviewed the flight crew, ground commanders, and witnesses. The investigation focused on the coordination between aerial and ground assets, the flight parameters of the helicopter, and the visibility conditions at the site.
Investigators analyzed the movement of the ground firefighting unit relative to the helicopter's flight path. They also evaluated the impact of the helicopter's flight speed and altitude on the distribution of the water drop. The investigation noted that the helicopter was flying at a ground speed of approximately 4 knots and an altitude of about 100 feet during the incident.
Findings
- Insufficient coordination: There was a lack of adequate communication and coordination between the helicopter crew and the Ground Firefighting Operations Party. This led to an overlap in their respective operational areas, with both units targeting the same location.
- Operational overlap: As the fire was nearing extinction, the active fire area had narrowed. The volunteer firefighter had moved into the area where the helicopter was performing drops, likely while the aircraft was away for refueling.
- Flight parameters: The helicopter was operating at a very low ground speed of 4 knots. At this speed, the water drop remains concentrated in an extremely narrow range, which increased the likelihood of a direct hit on anyone within the drop zone.
- Visibility and terrain: The heavily wooded, shrubby terrain made it difficult for the crew to spot personnel on the ground from the cockpit. Conversely, the ground firefighter did not see the helicopter in time to move to safety.