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ST. LOUIS COUNTY, MO (KTVI) – Viewer video of a large plane flying low over north St. Louis County attracted great interest from residents across the metropolitan area. After a day spent making calls and tracking the aircraft, Fox 2 News has solved the mystery.

Blannie Wagner, who sent the video to Fox 2, said she’d never heard something so loud. Wagner was inside her home Monday around 9 p.m. when the walls began shaking.

She lives just a few miles from St. Louis-Lambert Airport, so she’s used to hearing planes fly overhead, but this was different.

“I’ve got some experience with aircraft, but I’m no expert,” Wagner said. “I can judge altitude and it was definitely startling.”

Our news room made calls to Lambert, Boeing, the Federal Aviation Administration, Whitman Air Force Base, and Scott Air Force Base, and we tracked down an answer. The large plane was a Boeing KC-135 Stratotanker, a military aerial refueling plane.

A public affairs spokesperson for Scott Air Force Base said the aircraft was practicing touchdowns and takeoffs. The plane started at Scott, flew to Lambert, and then went back to Scott.

This particular KC-135 tanker belongs to the National Guard. It stands 41-feet high and 136-feet long, with a wing span of about 130-feet. With four turbofan engines, it’s certainly loud enough to startle anyone not expecting it, which is why so many north county residents were concerned.