INDIANAPOLIS - The commander of an Indiana Air National Guard unit is investigating why F-16s involved in training exercises created sonic booms two consecutive nights over north-central Indiana, shocking residents who also saw dazzling flares used in the missions.

A sonic boom and fireballs and flaming debris that Kokomo-area residents reported seeing in the sky Wednesday night prompted Howard County's police agencies to conduct a two-hour search for what many residents thought was a crashed aircraft.

As it turned out, the fireballs were flares fired by F-16s that are part of the 122nd Fighter Wing, an Indiana Air National Guard unit based at Fort Wayne International Airport.

Staff Sgt. Jeff Lowry with Indiana National Guard's headquarters in Indianapolis said the jets taking part in the training are not supposed to exceed the speed of sound, which is about 760 mph, because supersonic speeds produce sonic booms.

He said the 122nd's commander, Col. Jeff Soldner, will investigate why at least one jet reached supersonic speeds Wednesday night over Howard and Tipton counties, and also on Tuesday night over the Logansport area, shaking the ground below.

"The sonic boom is not routine. That was a mistake. That's being investigated right now and once the wing commander finds out he'll make recommendations on how to change that so it doesn't happen again," Lowry said.

He said F-16 training often involves the aircraft dropping flares from more than 10,000 feet above the ground, a technique that can allow the jets to evade heat-seeking missiles in combat.

Lowry said such flares are routinely dropped during the daylight hours and also at night but they likely would not have attracted much attention without the accompanying sonic booms.

The investigation will determine how many of the F-16s broke the sound barrier. Lowry said he did not know how many of the fighter jets were involved in the training missions.

The jets were training in an area called Hilltop Military Operations Area that's not designated for supersonic flights. The training area extends from Grissom Air Reserve Base to West Lafayette and includes Logansport, 30 miles north of Indianapolis bordering Kokomo.

Police switchboards in Howard and Tipton counties were inundated by calls after residents saw bright lights just before a loud sound like a sonic boom Wednesday night.

Smith's secretary, Janice Hart, said she was lying on her bed talking to her niece when a loud explosion rocked her home.

"It just shook my house to its depths. As soon as it happened, my niece said, 'Oh my God Aunt Janice, what was that?' I looked out my bedroom window and my husband went to the front of the house to see what it was," she said.

Hart, who initially thought an explosion had rocked a nearby factory, was busy Thursday morning handling calls about the noise and lights.

"That's all they're talking about. I had numerous calls asking if it was a sonic boom, a meteor, even some people joking that it was a UFO," she said.

Logansport Police Chief A.J. Rozzi said he heard a loud sonic boom on Tuesday night, and then heard the sound of a jet high overheard. He said residents also reported seeing fire streaks in the sky.

He said it is common for the 122nd to conduct missions in the area and believes F-16 training almost certainly explains the sights and sounds.

"They've been doing that training for quite a while. I don't know what maneuvers they're actually doing, but they do shoot out streaks of light," he said.