Down and Locked
Inspection and lubrication tips for landing gear systems
By Joe Escobar
Although every part and component of the aircraft is important, the landing gear is an especially critical system. It is the only means by which the aircraft is able to safely transition from flight to ground. Failure of the gear prior to or during landing can be catastrophic.
Recent NTSB reports show that there has been an increase in accidents and incidents attributed to landing gear problems. Numerous causes are listed ranging from part failures to improper maintenance. When you throw in the additional factor of severe operating conditions such as lack of pilot training and agricultural operations, the possibility of defects being present on the landing gear increases. The landing gear functions in some of the harshest operating and environmental conditions on the aircraft. Whether the landing gear is fixed or retractable, thorough inspections and lubrication are essential.
The first step of performing an effective inspection is to ensure that the gear is clean. Excessive dirt, grease, and other contaminants can hide otherwise easily visible flaws. Dirt and debris on the gear can cause binding in moving components such as actuators, chains, limit/indication switches and hinge points. A clean landing gear system ensures freedom of movement and ease of inspection.
A thorough visual inspection begins with a good light source. A good 10X magnifying glass also comes in handy at times.
Rich Mileham, Safety Manager for the Great Lakes Region FSDO, notes that cracks are the foremost area of concern when it comes to the landing gear. He adds that they are very difficult to detect. Some indicators of cracks include chipped paint, soot residue, or corrosion. Be sure to spend a little extra time on any areas of the system that have had a past trend of cracking. However, do not assume that just because you have never found a defect on any particular assembly that you can become complacent and not worry about looking at it very closely. All areas of the landing gear system deserve the utmost of attention when it comes to inspection. Be sure to follow the requirements of the maintenance manual and any applicable AD’s or Service Bulletins when performing the inspection.
Sometimes, it cannot be verified by a visual inspection whether or not an indication noted is a crack. This is where a NDT test comes in. Some AD’s require recurrent dye penetrant inspections on certain components. When performing a dye penetrant inspections, the issue of cleanliness is even more important. The greases and lubricants used for the landing gear system can set up in cracks. If not completely removed, these lubricants can prevent the penetrant from flowing into the discontinuity, causing false results in the test.
Some areas of the landing gear are particularly susceptible to corrosion. Areas where water can be trapped are especially susceptible. Any sitting water should be removed and the area inspected thoroughly. The ledges in wheel wells are particularly vulnerable to sitting water. Ensure that all drain holes are clear.
The area inside the axles is another corrosion prone area. Its relative inaccessibility makes corrosion removal difficult. The key is to find any corrosion early and remove it before it becomes a serious problem.
Some other areas to watch out for when it comes to corrosion are at dissimilar metal contact areas, under ferrules and identification tapes, and on wheel bearing races. Landing gear hardware is particularly prone to corrosion. All exposed hardware should be treated with corrosion preventive compound (CPC) as required.
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