N668DN accident at Atlanta, GA

A right engine turbine uncontainment resulting from failure of the high pressure turbine (HPT) lenticular seal due to a fatigue crack originating from an overheated region at a knife edge tip. Contributing to the failure was Pratt & Whitney’s decision to introduce the temperature-resistant knife-edge coating as a new-part number lenticular seal on an attrition basis without the option to recoat existing lenticular seals, which delayed implementation of the more durable seal material into the fleet.