Federal regulators started an investigation after an American Airlines jet lost a panel from its belly moments after taking off from the Dallas-Fort Worth International Airport.

The plane was on its way to Paris and lost the panel as it was flying over the Atlantic Ocean on April 20. The pilots heard the noise, but thought it was from the cargo shifting. The officials defended the jet’s crew in an internal memo.

All the people aboard the Boeing 767 felt and heard the noises. A flight attendant described it as "a loud shaking noise from the belly of the plane". The noise was followed shortly by another one that "sounded like an explosion." The flight attendant described the incident in an e-mail according to WFAA, a Dallas television station.

The jet continued its flight as if nothing had happened, but after the landing in Paris, the crew found out that a panel about two feet by three feet that was covering one of two air conditioners was missing.

After the discovery, the federal regulators initiated the investigation. American Airlines declined to comment on the matter. The AA flight department officials told the captain "did exactly what we want our captains to do," according to The Associated Press.

"There was no way this crew could have known this panel had departed. If they had known, they obviously would have returned," said in a memo Jim Kaiser, American's manager of flight operations quality control, and Chuck Harman, the airline's fleet captain for Boeing 757 and 767 planes.

The cockpit warning lights didn’t alert the pilots about the missing part, the memo said.
However, the airline’s officials said the passengers of the jet were never in danger.

The incident comes about a week after AA canceled approximately 3,300 flights as it grounded its fleet of MD-80 jets for electrical wiring inspection.