If you’re out and about this afternoon and see a jet flying a little too close to the city for comfort, don’t worry: it’s just the Department of Defense conducting a calibration flight.

DoD has announced that a civilian Cessna aircraft will be hovering but 1,000 feet above ground level over the District this afternoon between 1 and 4 p.m. Today’s exercise, which has “been carefully planned and will be closely controlled” by DoD, the Federal Aviation Administration and the Department of Homeland Security will serve to “assist in calibration of systems and equipment, and will serve to refine and improve our ability to respond to unknown and potentially threatening aircraft.”

Of course, commercial aircraft traffic is tightly restricted around the District (the map above outlines the air space restrictions around the area), so it’ll certainly be a rare sight to see a plane flying so low over the city.