An Air Self-Defense Force chief inspector said Wednesday his team found a glitch in an electric circuit that might have inadvertently caused an ASDF F-4 fighter jet’s 20mm cannon to fire into a civilian area in Hokkaido during an air-to-ground firing drill Monday. During testing, the jet’s 20mm cannon started operating without the trigger being pulled as an ASDF accident investigator shook the control stick with the armaments function turned on, said ASDF Maj. Gen. Yoshishige Hori, the inspector general.

They determined that an electric signal was sent to fire the cannon whenever the control stick was moved to a certain point, he said, adding that investigators have not yet determined how it was sent. Hori added that he has not yet determined if the malfunction affects just the one fighter or the whole F-4 inventory. Nationwide, there are 85 F-4 EJ Kai deployed, including the one involved in the accidental firing.

Hori said he had never imagined that a cannon could automatically fire just by moving the control stick.

The circuit glitch may not have been the sole cause of the incident, Hori said, adding that the ASDF will continue investigating the pilot as well as other factors.

The F-4, assigned to the Southwestern Composite Air Division in Naha, Okinawa Prefecture, fired 188 rounds Monday, some of which hit a rehabilitation center for elderly and disabled citizens in Kitahiroshima, Hokkaido. The jet was on a training mission over a nearby ASDF firing range at the time.

No one was injured, although some of the 7.7 x 2 cm rounds damaged structures and vehicles.

The pilot reportedly told inspectors that the cannon fired on its own and that he had neither pushed the fire button nor released the safety catch.

Meanwhile, a group of Diet members of the Social Democratic Party visited Defense Agency Director General Gen Nakatani on Wednesday and demanded that the air-to-ground firing range in Eniwa be relocated, saying the site is too close to residential areas.

Sekisuke Nakanishi, a Lower House member and vice president of the party, told the press after the meeting that the jet fighter would have fired into a residential area with several schools and a population of more than 20,000 had the cannon been at a slightly different angle.

He said the Eniwa training site, one of only two air-to-ground shooting ranges for the ASDF, is no longer suitable for such a drill, adding that the environment surrounding the area as well as shooting capabilities of fighter planes have drastically changed since the training site was set up some 40 years ago.

The SDP also demanded that the agency disclose more information on nationwide SDF training sites and ensure the safety of neighboring residents.

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