An unexploded WWII bomb closed a major airport in Japan Tuesday. Experts have determined it was American made and is believed to be a dud left over from World War II.

According to Yahoo! News, 92 flights in and out of Sendai Airport in Tokyo were cancelled after a 250-kilogram bomb was discovered during construction near a runway.  It was believed to have a working detonator which forced military bomb experts to decide whether to move it or explode it where it sat.

Sendai Airport is a major hub that's been undergoing reconstruction since the tsunami last year. It was during this reconstruction that workers made the discovery. As scary as this sounds, unexploded bombs are not unusual in Japan. The American military heavily bombed the area during World War II and dozens of duds are discovered each year. What makes them so dangerous is the rusty conditions of the workings. Experts say it could take several decades to remove all the unexploded devices.