In a move that has raised safety concerns, the U.S. Marine Corps’ Osprey transport aircraft, previously deployed in Okinawa, are now allowed to conduct low-altitude flights in other parts of Japan under a new bilateral agreement. The Japanese and U.S. governments have agreed to lower the minimum safe altitude for flight training of U.S. Ospreys in mountainous areas outside Okinawa from around 150 meters to about 60 meters, aligning with Japan’s aviation law.
The agreement, which took effect on July 10, was made following Washington’s request to Tokyo for practical training locations for the Ospreys. However, specific flight routes under the agreement have not been disclosed, leaving prefectural governments unaware, despite the normalization of low-altitude Osprey flights over the Japanese archipelago.
The altitude of about 60 meters is lower than certain power transmission towers in Japan’s mountainous regions. Pilots flying Ospreys at such low altitudes must have a deep understanding of the routes, considering the presence of wires used for wood transportation in the mountains. Moreover, to prepare for potential accidents, at least two Ospreys, including a rescue aircraft, are expected to fly together during training.
While Ospreys conduct low-altitude flights, there are also fire and disaster prevention helicopters and medical helicopters flying in the same mountainous areas. The aviation law permits these helicopters to fly below the minimum safe altitude for search and rescue purposes. However, this creates concerns about potential situations where they may come dangerously close to high-speed Ospreys flying at similarly low altitudes.
The National Governors’ Association of Japan has repeatedly requested prior information on low-altitude Osprey flights, but the Defense Ministry declined, citing that such information is related to U.S. military operations and cannot be disclosed.
The groundwork for full-scale low-altitude flights was laid when, in September to October of the previous year, the Japanese and U.S. governments agreed to temporarily lower the minimum safe altitude to about 90 meters. This measure was implemented during a field training exercise conducted by the U.S. Marine Corps and the Japanese Ground Self-Defense Force (GSDF) in Hokkaido.
As per the new agreement, U.S. Ospreys are restricted from flying in areas where Japanese SDF aircraft do not operate. The U.S. Marine Corps is required to provide advance notification to the SDF regarding training dates, time, number of aircraft, and flight routes. U.S. Ospreys may use airspaces utilized by the SDF.
There are nine SDF low-altitude training areas over Honshu, two of which were designated for use by U.S. military aircraft last year. These areas include mountainous regions straddling Tochigi, Fukushima, Gunma, Niigata, and Nagano prefectures, as well as an area near the U.S. military’s Iwakuni base in Yamaguchi Prefecture, which includes Shimane, Hiroshima, and Yamaguchi prefectures. These two areas align with established flight routes of the U.S. military over Japan, potentially serving as routes for Ospreys traveling between Okinawa and Japan’s mainland.
The safety of low-altitude Osprey flights came into question after an Osprey aircraft crashed in the United States in June of the previous year, resulting in five fatalities. The U.S. Marine Corps attributed the accident to a clutch problem known as “hard clutch engagement,” stating that there was no pilot error involved. However, this incident further intensified concerns regarding the safety of low-altitude flights conducted by Ospreys.