There were flight restrictions in place at the time, as President Joe Biden was in Delaware.
PHILADELPHIA (WPVI) -- It seems like most residents in the Philadelphia area heard a fighter jet fly over the city around 9:20 a.m. Monday.
According to NORAD, an F-15 fighter aircraft responded to a Cessna plane that entered a Temporary Flight Restricted area without proper clearance over Wilmington, Delaware.
President Joe Biden was in Delaware at the time.
The low-flying jet caught a lot of people off guard.
"I didn't see anything, but it sounded like a plane was actually about to crash land," said Michelle Crutchley.
"I got a little nervous because I didn't know where it was coming from. It sounded like some large thing above us, so it was a little scary," said Katie Aikins.
Officials said the aircraft exited the restricted airspace shortly after.
It was not yet clear what type of punishment the pilot could face.