Metal fatigue has emerged as the chief suspect in last week's spectacular engine failure on a United Airlines plane, which scattered debris over suburban Denver and led to dozens of Boeing 777 aircraft being grounded worldwide. Even prior to the Denver incident, US air safety regulators had been weighing stricter inspections on the jets and their Pratt & Whitney engines following a December 2020 incident in Japan, US officials said Tuesday. The FAA reviewed inspection records and maintenance history after a Japan Airlines fan blade incident on December 4, 2020 "to determine the cause of the fracture and was evaluating whether to adjust blade inspections," an FAA spokesman said Tuesday. The Japan flight landed without injury. While no one was injured in the Denver incident, the episode is the latest setback for Boeing, which only recently resumed deliveries of the long-grounded 737 MAX following two fatal crashes of that plane. The incident also raises fresh questions about the FAA, which was roundly attacked for its oversight of Boeing in the certification of the 737 MAX. Aviation experts say the Denver plane engine failure -- and earlier incidents involving Boeing 777s with...