Severe Corrosion Noted In Multiple Reports Through The Agency's SDR System

The potential for an undetected failure of flap cables due to corrosion on Textron Aviation Inc.(Textron) Beechjet Models 400, 400A, 400T, and MU-300-10 airplanes has led the FAA to issue a Special Airworthiness Information Bulletin for the airplanes.

The FAA has received multiple reports through the Service Difficulty Reporting (SDR) system of severe corrosion on the flap cables to the extent that cable separation has occurred in the flap well area where the cables connect to the swaged fittings on Textron Beechjet Models 400, 400A, 400T, and MU-300-10 airplanes. In some cases, the flight crew received annunciation of an asymmetric flap condition and landed the airplane safely. In other cases, the flaps continued to function and the pilot was unaware of the failed cable condition.

The flap cables on these airplanes are interconnected between left-hand and right-hand sides such that one side can drive or assist operation of the opposite side. However, continued operation in this state leaves the flap control system with less tolerance to subsequent failure(s).

Textron Aviation has issued Communique #126, dated June 2018, for the Models 400/400A to call attention to the need to clean and lubricate control cables on condition, and to do this more frequently when the airplane is operated in wet or salt laden environments. In any case, this cleaning and lubrication should be performed no later than every AB check. The FAA strongly encourages operators to follow the recommendation of Communique #126 for all Beechjet models listed on this SAIB.

(Image from file)

FMI: SAIB