SUDLERSVILLE, Md. - An electronic failure may be to blame for a practice bomb that was dropped from a jet onto a tavern's parking lot, a Maryland National Guard official said Friday.

An A-10 Warthog jet from the 104th Fighter Squadron in the 175th Wing was returning from a training mission Thursday night to Warfield Air National Guard Base in Middle River when the inert device was dropped, guard spokesman Lt. Col. Charles Kohler said. The guard has grounded the aircraft while it investigates.

Kohler didn't yet know exactly what device it was, but said it is made to fly like a 500-pund bomb, but weighs much less.

"This is an unfortunate incident and we're very lucky that no one was hurt. Safety is a top priority in all operations," Kohler said.

A customer at Darlene's Tavern in Sudlersville came in from outside saying he thought a car in the parking lot was on fire, said owner Darlene Hurley. The car was covered in dust and stones and a few feet away was a 3-foot deep hole, she said. They called 911.

Police officers dug in the hole and when they spotted the fins of the device, they called in the fire marshal's bomb squad, Hurley said.

Bomb technicians determined that it was a practice aerial bomb and the device was turned over to the National Guard, the fire marshal's office said.

"It could have been a whole lot worse. It landed about 100 feet from the building," Hurley said noting that there are propane tanks nearby. "It could have been really, really bad. Thank God everyone was OK."