WASHINGTON (CNN) -- An American Airlines plane flew from Dallas, Texas, to Paris, France, even though a "large panel" fell off the underside as the flight took off, the airline said in a memo to pilots.
Pilots and crew heard a noise and felt vibrations as the plane passed through 10,000 feet, but did not know the cause until they landed in Paris, according to the memo, which was obtained by CNN.
"There was no way this crew could have known this panel had departed," the memo says. "If they had known, they obviously would have returned."
Scott Shankland, a spokesman for the Allied Pilots Association, which represents American Airlines pilots, estimated the panel that fell off was roughly 3 feet wide and 4 or 5 feet long.
"There are pieces of the fuselage that are not monitored, and if they come off for some reason, we would have no way of knowing that happened," he said. "It's very rare. It does happen."
The Federal Aviation Administration said it is investigating the incident.
American Airlines issued the memo after angry e-mails and photos of the hole left by the missing panel, allegedly from members of the flight crew, began circulating on the Internet and airline industry blogs.
The carrier is not commenting officially on the April 20 incident other than to say it is investigating, spokesman Tim Wagner said. The memo is dated May 7.
The memo defends the pilot's decision to continue the 9½-hour flight, saying there were no warning lights, system abnormalities, further noises or vibrations.
"The captain decided to continue to [Paris' Charles de Gaulle airport], believing the noise might have been a cargo container shift," the memo said. It says that the pilot would have had to dump 100,000 pounds of fuel before returning to Dallas-Fort Worth International Airport, and that he had options to land before crossing the ocean if there had been further cause for concern.
A pilot would attempt an overweight landing only if there were serious doubt the flight could continue safely, said Shankland, the union spokesman and an AA pilot himself.
"Dumping the fuel would have taken over an hour, and you're talking about dumping tens of thousands of gallons of fuel over east Texas," he said.
The memo does not name the pilot of the 767 twin jumbo aircraft.
The FAA has apparently not issued directives to inspectors to check the particular panel that fell off the plane, suggesting there is no general history of problems with the part.
A wing panel blew off a US Airways plane somewhere over Maryland in March. Investigators later said they found cracked wing clips on the aircraft -- and on seven of the airline's 18 older Boeing 757s. All of the aircraft have been repaired, according to the independent National Transportation Safety Board, which is checking to see if other airlines' fleets could be affected.
A fatal Concorde crash in Paris in 2000 was apparently caused by a metal strip from another aircraft that damaged the Concorde on takeoff.
CNN's Mike Ahlers contributed to this report.
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