DALLAS (AP) - The feds are investigating how an Paris-bound American Airlines jet lost a panel from its belly after takeoff from Dallas-Fort Worth International Airport.

The Boeing 767 safely completed its April 20th trans-Atlantic flight before the problem -- involving a panel for access to an air conditioner -- was discovered by ground crews.

A Federal Aviation Administration spokesman says part of its probe centers on whether the pilot should have turned back.

The air conditioner area is separate from the cargo area and the pressurized cabin.

American is also investigating and wouldn't comment further. The pilot, Steve Kantlehner, could not immediately be reached for comment.

Officials in the airline's flight department told pilots in a memo obtained by The Associated Press that the captain "did exactly what we want our captains to do."

According to the memo, no cockpit warning lights came on, and the pilot also spoke to a maintenance technician in Fort Worth.

(Copyright 2008 by The Associated Press. All Rights Reserved.)

AP-NY-05-08-08 1423EDT