NORTH TEXAS (CBSDFW.COM) – People across two North Texas counties heard and felt it — but it wasn’t an explosion or an earthquake. It was a sonic boom.

It was around 10 a.m. that people all over Johnson and Hood County reported hearing a big “boom.”

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Shortly after the incident officials with Lockheed Martin Aeronautics confirmed they had tested a supersonic aircraft. The flight plan of the test flight was just from Fort Worth southwest toward Brownwood, about 135 miles away.

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Sonic booms or loud thunder-like noises are created when an aircraft travels faster than the speed of sound.

Officials with Lockheed said, “While the flight activity typically occurs at very high altitudes, atmospheric conditions sometime result in disturbances on the ground.”

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The test flight path runs through a corridor approved by the Federal Aviation Administration.