TOKYO: A Japanese Ground Self-Defense Force helicopter and its 10 crew members remained missing on Saturday, the third day since they disappeared near Miyako Island in the southernmost prefecture of Okinawa.

The chances of survival for those on board are believed to start falling sharply 72 hours after the accident.

The UH-60JA multipurpose helicopter is feared to have crashed. As the type of helicopter is highly reliable and used for disaster relief and emergency patient transport, a Defense Ministry official said, “We cannot even imagine what caused the accident.”

The chopper disappeared from radar around 4 p.m. Thursday, when wind speeds were approximately 6-7 meters per second. “At that (wind speed) level, helicopters can fly without problems,” a Maritime Self-Defense Force helicopter pilot said. “There also seemed to be no sudden changes in the weather.”

In 2017, an Air Self-Defense Force helicopter of the same type crashed off the city of Hamamatsu, Shizuoka Prefecture, central Japan. The crash has been found to have occurred after the pilot suffered so-called spatial disorientation, a condition in which a pilot is unable to interpret the aircraft’s attitude and altitude while in the air.

But a senior ASDF official said such a situation was unlikely in the latest accident. While spatial disorientation tends to occur when visibility is poor, such as at night and due to clouds or fog, the GSDF helicopter in question was flying to check topography with visibility of more than 10 kilometers.

The GSDF helicopter had undergone a regular inspection 10 days before the accident and showed no abnormalities during a flight just before the accident.

The type of helicopter has two engines, and it can fly even if one of them fails. Even if both engines stop, it can make a soft landing using a flight method called autorotation.

However, helicopter debris and other items discovered so far, including an unused lifeboat, suggest that the helicopter may have crashed so rapidly that there was no time to make emergency responses.

The senior ASDF official said that something inconceivable happened to the chopper, such as an accident in 2018 in which a GSDF helicopter crashed almost vertically after the main rotor fell out due to a bolt rupture caused by unknown reasons.

The GSDF and others are making every effort to find the missing crew members, as well as the helicopter and its flight data recorder, which are key to determining the cause of the accident.

JIJI Press