landing gear

Landing Gear Maintenance by Licensed Aircraft Engineers By John Routledge

During inspection and before removing any accumulated dirt, aircraft mechanics must closely observe the area being inspected while the wingtips are gently rocked up and down. Excessive motion between normally close-fitting landing gear components may indicate wear, cracks, or improper adjustment. If a crack exists, it will generally be indicated by dirt or metallic particles which tend to outline the fault. Seepage of rust inhibiting oils, used to coat internal surfaces of steel tubes, also assists in the early detection of cracks. In addition, a sooty, oily residue around bolts, rivets, and pins is a good indication of looseness or wear.

a. Thoroughly clean and re-inspect the landing gear to determine the extent of any damage or wear. MRO teams may discover that some components require removal and complete disassembly for detailed inspection. Other components may require the assistance of stress engineers to do a specific check using an ndt inspection process such as dye penetrant inspection, magnetic particle inspection, radiographic, ultrasonic, or eddy current inspection. The frequency, degree of thoroughness, and selection of inspection methods are dependent upon the age, use, and general condition of the landing gear.

b. Qualified technical staff must inspect the aircraft or landing gear structure surrounding any visible damage, to ensure that no secondary damage remains undetected. Forces can be transmitted along the affected member to remote areas where subsequent normal loads can cause failure at a later date.

c. Prime locations for cracks on any landing gear are bolts, bolt holes, pins, rivets and welds. The following are typical locations where cracks may develop.

d. Most susceptible areas for bolts are at the radius between the head and the shank, and in the location where the threads join the shank.

e. Cracks primarily occur at the edge of bolt holes on the surface and down inside the bore.

f. The usual types of failure in riveted joints or seams are deformation of the rivet heads and skin cracks originating at the rivets' holes.

g. Cracks and subsequent failures of rod ends usually begin at the thread end near the bearing and adjacent to or under the jam nut.

h. Cracks develop primarily along the edge of the weld adjacent to the base metal and along the centerline of the bead.

i. Elongated holes are especially prevalent in taper-pin holes and bolt holes or at the riveted joints of torque tubes and push-pull rods.

j. Deformation is common in rods and tubes and usually is noticeable as stretched, bulged, or bent sections. Because deformations of this type are difficult to see, feel along the tube for evidence of this discrepancy. Deformation of sheet-metal web sections, at landing-gear component attachment points, usually can be seen when the area is highlighted with oblique lighting.

When an aircraft experiences a hard or overweight landing, the aircraft mechanics should perform a special structural inspection of the aircraft, including the landing gear. Landing gear support trusses should be inspected for cracked welds, sheared bolts and rivets, and buckled structures. Wheels and tires should be inspected for cracks and cuts, and upper and lower wing surfaces should be inspected for wrinkles, deformation, and loose or sheared rivets. If any damage is found, a detailed inspection is recommended.

Landing gear retraction tests

Periodically perform a complete operational check of the landing gear retraction system. Inspect the normal extension and retraction system, the emergency extension system, and the indicating and emergency warning system. Aerosopace systems engineers must determine that the actuating cylinders, linkage, slide tubes, sprockets, chain or drive gears, gear doors, and the up-and-down locks are in good condition and properly adjusted and lubricated, and the wheels have adequate clearance in the wheel wells. In addition, an electrical continuity check of micro-switches and associated wiring is recommended. Only qualified technical personnel should attempt adjustments to the gear position and warning system micro-switches. Follow the manufacturer's recommendations.