Comment from Kyle Mullen

I support the FAA's goal of addressing potential structural fatigue on Boeing Model 747-8 airplanes but oppose finalizing this proposed Airworthiness Directive without additional technical justification for applying the inspection requirements to the entire affected fleet. According to the notice, the FAA's proposal is based on cracks discovered on Boeing Model 747-400 airplanes and fatigue-test findings on a Boeing Model 747-100 airframe. The FAA also acknowledges that no cracks have been reported on Model 747-8 airplanes, and instead concludes that the -8 series may be subject to the same unsafe condition because of similar lap splice design and fatigue stresses. Before issuing a final rule, the FAA should provide additional engineering analysis demonstrating that the fatigue behavior of the 747-8 fleet is sufficiently comparable to earlier 747 models to justify identical repetitive inspection requirements. Although similarities in structural design are relevant, differences in manufacturing methods, operational history, utilization rates, and accumulated flight cycles may affect fatigue crack initiation and growth. The FAA estimates that only three U.S.-registered airplanes would be affected and that each inspection cycle would require approximately eight labor hours at an estimated cost of $680 per airplane, while also acknowledging that it lacks sufficient data to estimate potential repair costs. Because repair costs are currently unknown, operators would benefit from additional information regarding the expected frequency, severity, and likely repair scenarios associated with any detected cracking. The FAA correctly notes that widespread fatigue damage can eventually compromise structural integrity and lead to rapid decompression if left unaddressed. However, before extending inspection requirements to aircraft on which no cracking has yet been identified, the Agency should publish additional technical data explaining why the available evidence supports the proposed inspection intervals and applicability. I encourage the FAA to supplement the administrative record with additional fatigue analysis specific to the 747-8 fleet and to consider whether a risk-based compliance schedule could provide an equivalent level of safety while minimizing unnecessary inspection burden on operators.