After four months of hand wringing and headlines, the Federal Aviation Administration approved Boeing’s retrofit battery-system design for the 787 Dreamliner on April 19. This move allowed Boeing and the eight airlines that operate the high-tech aircraft to begin modifying the 50 that have been delivered and were grounded in January. Ethiopian Airlines became the first operator to restart commercial flights on April 27, followed by Qatar Airways on May 1.

The two largest Dreamliner operators, All Nippon Airways, which owns 17 of the jets, and Japan Airlines, which has seven, are in Japan and will start up flights in June....