Boeing issued a Service Letter on December 19 2024 that addresses a critical maintenance issue on the 747-8 and 747-8F aircraft involving the Leading Edge (LE) Flap System's Geared Rotary Actuators (GRAs), specifically at positions 1E, 1, 26, and 26E. Multiple in-service reports have highlighted actuator seizure due to internal corrosion and spline wear, leading to flap skew without triggering flight deck warnings. Such failures can go undetected and pose safety and operational risks during takeoff.
The root cause is primarily moisture ingress caused by cold-soak conditions and exposure to runway de-icer. These conditions are exacerbated in outboard flap locations that experience extreme cold (as low as -40°F), far from the engine bleed air heating system. Secondary contributors include out-of-tolerance cap drive bores and over-pressed ball bearings, with some design corrections implemented by the supplier in 2023.
Seized actuators showed heavy corrosion and spline wear after 25,000–50,000 flight hours and 5,000–10,000 cycles. Because the actuators cannot be serviced on-wing, Boeing recommends a soft-time overhaul of affected actuators after 30,000 hours or 5,500 cycles.
Operators are advised to overhaul the eight GRAs at the noted positions and may adjust intervals based on their own fleet experience. Curtiss-Wright is the designated repair vendor. Boeing outlines an estimated labor of 6.5–8.5 hours for replacing a single actuator, with additional time if multiple actuators are addressed simultaneously.
No warranty coverage is offered for these actions. This recommendation replaces prior interim actions and establishes a permanent preventive maintenance strategy to mitigate service disruptions and undetected flap misconfigurations.