WASHINGTON — A federal air marshal on a flight earlier this month from England to New York left her loaded service weapon in the aircraft’s bathroom where a passenger found it, four marshals familiar with the incident said.

The passenger gave the weapon to a member of the flight crew, who returned it to the air marshal. But the marshal, who is based in the New York region, failed to report the incident to her superiors, as required by agency policy, until several days later. The incident happened on April 6, aboard a Delta flight from Manchester to Kennedy International Airport.

Despite the security lapse, the marshal was assigned to a flight a few days later, people familiar with the case said.

The Transportation Security Administration, the parent agency of the air marshal service, said that it was aware of the episode but that it would not comment publicly on internal matters, adding that it was “reviewing the circumstances of this incident.”