NTSB Recommends FAA Action on Fan Blade Crack Detection
The National Transportation Safety Board recommends the FAA determine minimum crack size and inspection limits for repaired JT9D engine fan blades.
The NTSB recommends that the Federal Aviation Administration determine the minimum size of patch repair processing cracks that could initiate fatigue cracks in Pratt & Whitney JT9D model engine fan blades and determine the limits of the eddy current inspection or other inspection techniques to detect such cracks. If the minimum size of the patch repair processing cracks is smaller than the detectability limit of the inspection, issue an airworthiness directive to require on all blades that have been patch repaired, recurring inspections capable of detecting a propagating fatigue crack before it reaches a critical length.
Original regulatory source: https://data.ntsb.gov/carol-main-public/sr-details/A-90-008