By Marilyn Adams

and Alan Levin
USA TODAY

United Airlines has found evidence of a small defect in the tail section of one of its Airbus jets, officials told USA TODAY.

United and Airbus officials say the defect isn't significant enough to warrant repair, and the jet is being returned to service. But it's the first evidence of a flaw in an Airbus jet since a 27-foot tail fin tore loose on an American Airlines Airbus A300. It crashed Nov. 12 in New York, killing 265 people.

United mechanics found the flaw, a tiny separation in the composite material, in the area where the vertical tail fin connects to the fuselage. Airbus officials say this defect does not mean there is a design problem with its jets.

However, the discovery will be examined closely by crash investigators.

The mechanics found the defect by using an ultrasound test. The discovery is likely to increase calls for broader ultrasonic testing of composite material on passenger planes.

The Federal Aviation Administration and French authorities ordered visual tests of A300 and A310 jet tails after the crash, and no damage was found. But a visual test cannot detect defects within composite material. The United jet, an A320, is a different model from the one that crashed but has a similarly constructed tail fin.

United decided to test three Airbus jets with vertical stabilizers that had been repaired at the factory before delivery. Airbus had detected flaws inside the composite material on those jets. The American Airlines Airbus jet that crashed had a similar factory repair.

United's ultrasound test this week on the 6-year-old A320 found a flaw on the opposite side of the stabilizer from where the factory repair had been made.

''We found a small ply separation . . . on the other side of the tail,'' said Lou Mancini, United's vice president for engineering. ''You can't see it -- the indication showed up on an ultrasound test. We think it had been there since manufacturing.''

Mancini said the airline notified the FAA, and United will soon test its other two Airbus jets. The FAA is keeping a close eye on the issue, said spokeswoman Laura Brown, but so far doesn't believe there is a safety risk.

Airbus spokesman David Venz said the defect is in an area that doesn't support the weight of the tail. ''We are confident this airplane is fit to fly,'' Venz said.

Wednesday, composites experts said it is possible that a minor defect could exist in the carbon-fiber structure and create no danger. One benefit of composites is that they tolerate some types of damage better than metals.

A source connected to the crash investigation said ultrasonic tests may be needed to gauge whether jets have defects. So far, the investigation has not found evidence that the tail of the A300 that crashed was damaged, but the examination has barely begun