Conditional Inspection
Last updated
Last updated
This section describes a thorough examination of the main rotor hub assembly and its parts, to a level defined by BELL, to detect structural failure, deterioration or damage; and to determine the need for corrective maintenance.
If the following evaluation requires the replacement of any part, also replace both tension-torsion straps, both strap pins, and both strap bolts.
Carefully inspect all detail parts visually for any apparent damage or abnormal appearance. Visual defects that are cause for replacing the entire hub include the following:
Pitch horn pulled from grip.
A segment of sheared mast attached to trunnion.
Obvious deformation of any other detail part within the hub would cause only the part that is deformed to be replaced along with both tension-torsion straps, both strap pins, and both strap bolts.
Any detail part within the hub that has sustained surface damage shall also be subject to normal inspection procedures. Surface damage in excess of overhaul limits will require replacing only the damaged part along with both tension-torsion straps, both strap pins, and both strap bolts.
Dimensionally check for indications of permanent deformation or damage to parts as specified. A dimensional discrepancy of any part will cause only that part to be replaced along with both tension-torsion straps, both strap pins, and both strap bolts, unless stated otherwise in the following detailed evaluation procedure.
Check yoke precone angle and spanwise straightness by inspecting machined surfaces of yoke with a straight edge. Yoke lower surface is not to be included in this inspection. Replace hub assembly if there is a deviation of more than 0.001 inch (0.025 mm) per 1.0 inch (25 mm).
Inspect pillow block bore diameter for out-of-round condition. If out-of-round condition exceeds 0.001 inch. (0.025 mm), remove primer and cadmium plate and remeasure. If bore is still out-of-round in excess of 0.001 inch (0.025 mm), replace pillow block.
Inspect pillow block for wear where thrust washer abrades it. Inspect wear disc for looseness if installed.
Inspect pillow block bolts for shear offset (straightness). Replace hub assembly if any evidence of bolt yielding is found.
Inspect retainer for alignment and damaged threads. Inspect attaching nuts for damaged threads.
Inspect balance washers for damage and straightness. Inspect attachment holes for cracks on outer and inner surfaces of yoke.
Inspect holes for blade bolts, blade bolt bushings, and bolt holes for strap bolts to ensure roundness within 0.001 inch (0.025 mm). Elongation of grip bushings in excess of 0.002 inch (0.050 mm) is cause to replace entire hub.
Inspect mating surfaces between grips and pitch horns for deformation. Surface deformation greater than 0.0015 inch (0.038 mm) is cause to replace grips and pitch horns.
Inspect surface of pitch horns for deformation on a surface plate. Horn deformation greater than 0.002 inch (0.050 mm) is cause to replace the horns.
Inspect inboard lug surfaces of pitch horn trunnion for deformation. Lug surfaces must be parallel to pitch horn and to grip surfaces. Deformation greater than 0.0025 inch (0.063 mm) per 1.0 inch (25 mm) of surface length being inspected is cause to replace pitch horn.
Remove dry film lubricant from shank of blade bolts by scrubbing with Abrasive pad and MEK.
Measure shank diameter of blade bolts in at least six locations. If diameters vary more than 0.0007 inch (0.017 mm), replace blade bolts.
Roll blade bolts on a surface plate. A deviation greater than 0.0015 inch (0.038 mm) is cause to replace blade bolts.
Measure shank diameter of strap bolts in at least six locations. If diameters vary more than 0.0008 inch (0.020 mm), remove cadmium plating and remeasure. If diameters vary more than 0.0005 inch (0.012 mm), replace straps bolts.
Roll strap bolts on a surface plate. A deviation greater than 0.0015 inch (0.038 mm) is cause to replace strap bolts.
Inspect static stops for cracks or deformation. Replace stops if damage is evident.
Dimensionally check for indications of permanent deformation or damage to parts. If a dimensional discrepancy is found on any part, replace only that part unless otherwise stated.
Place one spindle of trunnion in a V-block. Mount a dial indicator on opposite spindle. Rotate trunnion. Indicator reading should not exceed 0.004 inch (0.10 mm).
Perform normal inspection.
Methyl-Ethyl-Ketone (MEK)
Abrasive pad