The investigation into an engine explosion on a jetliner taking off from Denver is focusing on a fan blade that appeared to be weakened by wear and tear, a development reminiscent of a fatal failure on board another plane in 2018.
These and other recent engine failures raise questions over long-held assumptions about how long fan blades last and whether they are being inspected often enough.
A Boeing 777 operated by United Airlines had to make an emergency landing in Denver after one of its engines blew apart, spewing huge chunks of wreckage that landed in neighbourhoods and sports fields. Passengers captured video of the crippled engine, wobbling and still on fire, as pilots made a safe return to the airport minutes after the plane bound for Hawaii took off.