New York (CNN Business) Investigators of a fatal accident on a Southwest Airlines plane last year recommend that Boeing retrofit the engines of nearly 7,000 jets to prevent a repeat of the accident.

single passenger was killed on the plane when a fan blade broke and caused part of the engine covering to hit the side of the jet. That broke one of the windows, and the cabin rapidly depressurized. The crew was able to land the plane, but the woman sitting next to that window was killed.

The National Transportation Safety Board, which investigated the accident, recommended Tuesday that Boeing redesign part of the outer covering of the planes' jet engines to prevent it from flying into the plane should a fan blade break free on a future flight. It said that all Boeing 737 Next Generation series airplanes should be retrofitted with whatever fix Boeing comes up with.

Boeing has delivered about 6,700 of the 737 NG jets to airlines around the world, but it has stopped taking new orders for them as it shifted to the 737 Max. It has fewer than 100 of the NG planes yet to build and and deliver.

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