Japan's Ground Self-Defense Force said Thursday that it has been unable to determine the exact cause of the engine troubles that caused a deadly crash involving one of its helicopters off an island in the southern prefecture of Okinawa in April 2023.
In its investigative report on the accident, which killed all 10 personnel on board, the GSDF described the nearly simultaneous engine failures as an "unprecedented event." However, it will fully resume operations of the same type of helicopter, although no date has been specified.
The force also pledged to take necessary measures to prevent any similar accidents from happening again, such as strengthening flight safety surveillance.
"Taking the accident seriously, we will thoroughly ensure the safety of our flights, with the determination to avoid any loss of human life in the future," Gen. Yasunori Morishita, chief of staff of the GSDF, said at a press conference.
The UH-60JA helicopter disappeared from radar at 3:56 p.m. on April 6 last year, 10 minutes after taking off from a base on Miyako Island in Okinawa Prefecture, with no abnormalities reported. The incident was the deadliest ever involving a GSDF aircraft.
After analyzing the wreckage and recovered flight recorder of the helicopter, which had two engines, it was noted that both saw a sudden reduction in power before the crash, making it difficult for the chopper to "maintain altitude," the report said.
The engines were supposed to serve as backups to each other but the output fell in both, one after the other, within 90 seconds of the helicopter crashing, in an event that "has never before been reported," the report added.
No links were found concerning the problems both engines experienced, GSDF officers told reporters. The right engine was hit by a "rollback," a rare failure that gradually decreases an engine's output, which was not mentioned in the aircraft's handling manual.
Rollbacks generally occur due to an engine experiencing fuel supply shortages or due to some other abnormality in the control system, according to the officers.
The report, meanwhile, concluded that the cause of the left engine's failure could not be specified. The GSDF also ruled out factors such as those involving weather conditions and daily maintenance work as possible causes of the accident.
The GSDF currently operates 39 UH-60JAs, which were first deployed in 1997 to transport relief supplies to natural disaster-hit areas and conduct rescue activities, the officers said. Drills involving the aircraft partially resumed in June 2023.
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