Wichita, KS – At their recent Customer Conference, Textron Aviation provided some clarification and cautions related to the presence of corrosion in King Air series aircraft. With a series of photographs, Bob Godshall, Manager of Turboprop Product Support, showed the importance of proper corrosion checks and mitigation procedures.
According to Godshall, all of the metals used on the King Air series aircraft are prone to corrosion for various reasons.
“When working on or around the aircraft,” Mr. Godshall says, “it is critical to be on the lookout for any signs of corrosion.”
Pilots and mechanics should look for paint bubbles, especially around attachment hardware, FOD (foreign object damage) that might cause galvanic or bimetallic corrosion from dissimilar metals coming into contact, and wet surfaces inside a closed area. This is typically a mechanic check, but Godshall did mention a particular place pilots should look: “moisture, dirt, and foreign objects [in the cabin and cockpit seat tracks] left untreated WILL cause corrosion.” King Air interior corrosion issues are often caused by drink spills, water being tracked in, or rain blowing through an open door and pooling in the seat tracks. All are easily avoidable issues, but have been the culprits leading to corrosion and eventual metal failure on several aircraft.
Most importantly for mechanics, Godshall pointed out, is water inclusion inside the wing and the horizontal stabilizer. Of particular concern are the areas around the main wing spar cap where dissimilar metals contact, the area around the center section main spar for both the wing and the horizontal stabilizer, and areas in the belly of the aircraft where water tends to pool. In some instances, very minor corrosion has been allowed to continue to the point of holes developing in the wing or h-stab spars, and has let to aircraft being totaled, either upon inspection or after mechanical failure. Mr. Godshall showed one instance where corrosion of two “7 cent bolts” caused the total loss of an airframe.
In addition to close monitoring for the conditions mentioned above, Godshall suggested several other steps for corrosion control.
Most importantly, he noted “Beechcraft’s position is that operators have to be inspecting for corrosion to maintain their airplanes in a condition at least equal to original condition.”
Godshall emphasized that all of the metals used in the production process are susceptible to corrosion without proper treatment. With that in mind, Mr. Godshall says “chemical cleaning, pretreatment, and priming are used during the manufacturing process,” so it is important that operators keep these metals protected in a similar manner. Painting, re-priming, and freshwater washes are just some of the ways of protecting these corrosive metals.
The King Air AMM, chapter 12-20-03, highlights procedures to follow during aircraft cleaning. Godshall says a regular cleaning schedule, to include the inside sections of the wing and horizontal stabilizer, should be established and maintained, especially in parts of the world most prone to corrosion. Once the new chapters 5 and 20 of the AMM are released they will discuss further proactive measures for identification, protection, prevention, and control of corrosion.
“In summation,” Mr. Godshall says, “keep all areas painted as required…this will keep the high-strength aluminum alloy (alclad) protected. Once the alclad is penetrated the corrosion process is accelerated.”
For more information or to see the Corrosion Severity Maps, visit www.beechcraft.com.