An investigation is underway into how a gun carried by a US Airways pilot was discharged during a flight.
No-one was hurt when the gun went off as the plane was preparing to land at Charlotte, North Carolina, on Saturday.
A hole in a cockpit wall apparently caused by the shot is visible in photos obtained by AP news agency.
Under a programme implemented after the 9/11 attacks, US airline pilots are allowed to carry guns on domestic flights following a training course.
The gun discharged just before noon on Saturday aboard Flight 1536 from Denver to Charlotte, as the Airbus A319 plane was at about 8,000 feet and was approaching to land.