ATA 72

Acoustic Fatigue May Cause Engine Inlet Cracking
If you are an operator or technician who is dealing with an engine inlet that continuously cracks, consider accomplishing an acoustic survey. Engines with fans that are balanced but have blades that have been blended or cropped may generate noise that can cause acoustic fatigue. If replaced fasteners loosen or cracks continue to appear in the inlet, the engine may be experiencing this condition. Every 200 hours a visual inspection of the engine inlet is required per Chapter 5-20-07 of the Westwind1124/1124A Maintenance Manual. Pay close attention to the inlet aft frames and barrel for cracks, as well as inspecting the entire structure for loose and missing rivets. An acoustic survey could determine if this noise is the cause of the problem and possibly help you avoid costly inlet repairs.