At around 8PM of October 26, 1986, Thai Airways International Flight 620 (Airbus A300-600, Registration HS-TAE) was cruising above Tosa Bay off the coast of Kochi Prefecture, carrying 14 crews and 233 passengers, when the rear of the aircraft suddenly suffered an explosion, resulting in rapid decompression and damage to the rear pressure bulkhead, severing two of the three hydraulic pipes. As a result, the aircraft veered off course for about 100 kilometers and into restricted air space of the Japan Air Self Defense Force, as well as going into a dutch roll at one point, but the aircraft managed to make an emergency landing at Osaka Itami Airport at 8:40 PM.^[9][10]

As a result of the explosion and the aircraft's violent turbulence, a total of 109 passengers and crew suffered injuries, with 14 of them suffering severe injuries.^[11]

Initially, it was believed that, like Japan Air Lines Flight 123 a year before, some sort of a mechanical problem was to blame for the incident.^[12] While the aircraft was delivered less than three weeks before the incident, the pressurization devices were having issues in the week leading up to the incident, with reports being made that warning lights were turning on.^[12]

However, it was quickly revealed after the aircraft was examined by the Osaka Prefectural Police [ja] that the explosion was caused by some sort of an explosive that was brought in, rather than the aircraft itself.^[4][13] Ultimately, a 43-year-old yakuza of the Yamaguchi-gumi admitted to smuggling the hand grenade into the aircraft. The yakuza stated that he "accidentally pulled the safety pin off in the toilet that was at the rear left area of the toilet" and that "he tried to put the pin back in, but it didn't work, so he left it behind in the toilet and let it blow up".^{[2][3][5][10][14]}

The yakuza who brought in the hand grenade was not arrested until after he was discharged from the hospital, because the man had suffered severe burns all over his body as oil from a broken hydraulic pipe poured over him during the incident.^[3]

The aircraft involved, HS-TAE, was delivered less than three weeks before the incident on October 9.^[11][12] As such, the aircraft was flown back to Bangkok with quick repair done at Osaka, and later a full repair was done and subsequently returned to service. The aircraft continued to fly for Thai Airways International. In 2008, the aircraft was transferred to Unical Aviation and registered as N395EF. The aircraft has since been scrapped.^[15]

As of April 2024, Thai Airways International still uses Flight 620 for one of its Bangkok-Manila flights, though the flight no longer continues to Osaka.^[16] After the airline retired its Airbus A300-600 fleet, the flight now typically uses Boeing 777-200ER aircraft, although a variety of other aircraft is occasionally deployed, including the Airbus A330-300 and the Airbus A350-900.^[16]