(Reuters) - The U.S. National Transportation Safety Board on Tuesday called on Boeing Co BA.N to redesign the fan cowl structure on all 737 NG planes and retrofit existing planes after an April 2018 incident in which a woman was killed on Southwest Airlines LUV.N plane after an engine failure caused by a fan blade.

The board said the Federal Aviation Administration should require Boeing to determine the fan blade impact location or locations on the engine fan case and redesign the structure. The board did not fault Boeing’s analysis in the mid-1990s when it developed the case. Boeing did not immediately comment.