Was it a sonic boom? People searched for that too. After the military initially said it wasn't one of their aircraft that created the loud boom, Naval Air Station ... of the test flight, a ...

User-supplied instruments that have not flown on the King Air previously and may have either no flight experience at all or little but ... applications also have flown on the King Air to test ...

NASA and Boom Supersonic ... that detect air distortions. That's why the shockwaves around the aircraft are visible in the photograph. NASA also gathered sound data from the test flight.