Everything you need to know about the surprise ‘sonic boom’

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Target 3 explains how a Boeing fighter jet broke the sound barrier and set off a loud boom

SPRINGFIELD, Ill. (NEXSTAR) — Phone lines, group chats, and email inboxes lit up with a flurry of curious questions at local police stations, fire houses, city governments, and newsrooms just after 11:00 a.m. on Tuesday morning. The question echoing across Central Illinois was, ‘What was that loud boom that rattled windows, houses, and nerves?’

Social media sleuths were quick to offer possible explanations. Some wondered if it was an earthquake. Others suggested an explosion at a chemical plant. WCIA3 Chief Meteorologist Kevin Lighty, a licensed drone pilot with the Federal Aviation Administration, was among the first to suggest it was a ‘sonic boom,’ created by a jet breaking the sound barrier.

WCIA3 Chief Meteorologist Kevin Lighty tweeted, “This aircraft flew across many parts of central Illinois well in excess of 750mph.”

Within minutes of the disturbance, the Illinois Emergency Management Agency was on the case, looking to quell concerns from a panicked public. In a statement, IEMA officials said the noise disturbance triggered “an immediate collaboration between federal, state and local officials to identify the impact and source of the incident.”

According to sources on that call, Boeing, one of the nation’s largest defense contractors, informed the state that pilots with the the Department of Defense were taking one of their new F-15EX Strike Eagle II fighter jets out for a “final acceptance,” which is somewhat of a test drive before completing the transaction.

“Upon further review, it was determined that an F-15 fighter jet in the airspace above central Illinois course corrected creating a sonic boom,” IEMA spokeswoman Rebecca Clark said later in the afternoon. “When the aircraft broke the sound barrier, the pressure wave created an audible noise and minor shaking in the region.”

Aviation records show the flight path traveling from Pittsfield, Illinois, across state lines into Missouri, before circling back in a straight line toward Decatur, reaching a top speed of 1,148 miles per hour. The jet landed safely at the St. Louis Lambert International Airport at 12:30 p.m., less than an hour and a half after takeoff.

Aircraft can create a ‘sonic boom‘ anytime they fly faster than 750 miles per hour. According to publicly available flight records, the Boeing jet was traveling above the sound barrier at an altitude higher than 40,000 feet for roughly two minutes.

A Boeing promotional video described the jet’s roar as the “sound of freedom.” The U.S. Air Force says the shock waves from a sonic boom carries enough power to shatter glass in buildings at ground level.

Clark offered assurances there were “no reports of damage associated with the incident.” But the loud boom that sent local and state governments scrambling to assure the public of its safety raised questions about the lack of notice that caught so many people off guard.

Sectional aeronautical charts at the FAA designate specific zones of jurisdiction in the skies that allow military aircraft to perform tests.

The Tuesday morning test flight appears to have taken off from inside of a Military Operational Area (MOA) in Pittsfield. Fighter pilots often simulate combat missions in these spaces, and are not subject to any “speed limit,” per se. While the pilots do communicate with air traffic controllers if they enter their radius, they may not notify local officials in advance of their test runs.

The training missions themselves are rather routine. It was the speed of this particular flight that was extraordinary. Jets cast a wider, but softer impact “sonic boom” the higher they go. According U.S. Air Force estimates, people could’ve felt Tuesday afternoon’s supersonic impact from as far as 46.5 miles away from the jet’s flight path.

When the first reports surfaced in Springfield, the Abraham Lincoln Capital Airport notified the mayor’s office that they were not aware of any flights that would’ve been in their radius. That turned out to be true. The F-15’s flight path never entered the 10-mile radius surrounding the Springfield airport, but its pilots would’ve communicated with air traffic controllers in St. Louis.

According to an official release from the U.S. Air Force, Boeing contracted with the Department of Defense to deliver this most recent batch of eight, new F-15 EX jets cost taxpayers $1.2 billion.

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