There's an existing inspection period of every 6,500 takeoffs and landings[1]. The expectation is that it would take sufficiently long for a detectable flaw to

There's an existing inspection period of every 6,500 takeoffs and landings[1]. The expectation is that it would take sufficiently long for a detectable flaw to turn into a dangerous fracture that this would be sufficient to notice it. But, given this failure (and presumably also because of the 2018 one), that assumption appears to be untrue. Checking all of them now and comparing any discovered defects to the number of cycles since they were last checked should allow a recalibration of how frequent checks should be (or, if there's an indication that flaw propagation is significantly faster than anyone expected, potentially stronger measures) [1] My understanding is that it's based on cycles rather than flight time because takeoff is the part of flying that puts the most stress on the blades - spending 10 hours in cruise isn't much worse than spending 2.