AD 2021-22-12 Requires Removing And Cleaning The Inner Diameter Of The Flap Control Pushrods...

The FAA is adopting a new airworthiness directive (AD) for certain Honda Aircraft Company LLC (Honda) Model HA-420 airplanes.

This AD was prompted by a report that the flap pushrod assemblies are susceptible to corrosion. This AD requires removing and cleaning the inner diameter of the flap control pushrods and repetitively applying corrosion inhibiting compound (CIC) to this area. The FAA is issuing this AD to address the unsafe condition on these products. This AD is effective November 19, 2021.

Supplementary Information: The FAA was informed by Honda that the inner diameter of the flap control pushrod assemblies for certain Honda Model HA-420 airplanes are susceptible to corrosion, reducing the capability of the flap control pushrod to withstand normal operating conditions and resulting in its eventual failure. The corrosion was initially discovered during scheduled maintenance when a visual inspection of the flap control pushrod assemblies revealed signs of corrosion at the drain holes of the welded tube center section of inboard and outboard assemblies. Later borescope inspections of the same airplane inside the welded tube section revealed pitting and discoloration of interior walls. On a later scheduled inspection of another airplane, similar corrosion was noted.

While the specific root cause of the corrosion is still under investigation, the flap control pushrods on the affected airplanes are susceptible to corrosion because the material of the pushrod is a low-alloy steel that had incomplete coverage of primer and CIC in the inner diameter. This incomplete coverage is potentially due to welding process spillover material creating voids that the primer could not reach and is exacerbated by general incomplete application. Drainage holes in the flap pushrod allow the external environment direct access to the inner diameter of the tube, exposing the improperly treated surface to the elements. As a result, corrosion may begin to develop immediately after the airplane enters service.

As a large majority of the fleet have been in service for longer than 12 months, during which time corrosion has progressed, the FAA finds the need for immediate action to preclude failure of the flap control pushrod. The compliance time of this AD prioritizes the affected fleet by risk and simultaneously requires all airplanes to be serviced as soon as possible.

Failure of a flap control pushrod, if not prevented, could result in uncontrolled and un-annunciated flap asymmetry, which could result in loss of control of the airplane. The FAA is issuing this AD to address the unsafe condition on these products.

FMI: www.regulations.gov