Inspections

This section gives the procedure and data necessary to visually examine the main rotor hub assembly and its parts for specific defects/failures.

Preliminary Requirements

Consumables, materials and expendables

Cadmium plating solution (LDC 4803)

ThixO SYN (3820-0)

Epoxy Polyamide Primer

Safety Conditions

CAUTION DO NOT REMOVE CADMIUM PLATING FROM COMPONENTS EXCEPT FOR REPAIRS.

If records or physical appearance of main rotor hub indicate the assembly has been subjected to an accident or incident outside the realm of normal usage, perform conditional inspection. If the main rotor hub does not require conditional inspection, proceed with normal inspection.

Limit charts are provided to show required fit between mating parts and provide dimensions as a guide for replacement of worn parts. It is not intended all dimensions listed on limits charts be checked as a prescribed overhaul procedure; however, parts showing evidence of wear or physical damage shall be checked dimensionally.

If any main rotor hub part shows indications of excessive wear or is not within tolerance, check mating part for abnormal wear.

Normal Inspection

1. Inspect trunnion, strap fitting, strap pins, strap bolts, latches, blade bolts, retainers, radius rings, pitch horns, static stops, pillow blocks, and plug for cracks, mechanical damage, and corrosion. Replace parts that are cracked and/or exceed limits.

Trunnion

Trunnion - Damage Limits

Strap Pin

Strap Pin - Damage Limits

Strap Bolt and Blade Latch

Strap Bolt and Blade Latch - Damage Limits

Blade Bolt

Blade Bolt - Damage Limits

Retainer

Retainer - Damage Limits

Radius Ring

Radius Ring - Damage Limits

Pitch Horn

Pitch Horn - Damage Limits

Pillow Block

Plug

Blade Bolt Plug - Damage Limits

1. Inspect the following main rotor hub parts dimensionally for wear and damage. Replace parts that exceed limits.

Yoke

• Inspect yoke for evidence of corrosion and mechanical damage. Special attention shall be given to pillow block bores, inboard bearing journals, wear sleeve journals, and mating fillet radii.

• Inspect interior of yoke for damage to primed surfaces. Touch up as required with Epoxy polyamide primer.

• Inspect cadmium plated surfaces of yoke for condition. Apply Cadmium plating solution as required (BHT-ALL-SPM, Chapter 3, Standard Practices Manual).
• Inspect yoke for mark from flap restraint arms.

A main rotor yoke, which would be rejected solely due to excessive corrosion damage in outboard bore of spindle, may be repaired by an approved service facility. Repair consists of machining and installation of a special insert in bore. Once installed, the insert cannot be removed or replaced except by approved service facility.

• Visually inspect bearing journals on yoke for roughness, spalling, scoring, pitting, flaking, etc.

• If yoke has excessive corrosion damage in outboard bore of spindle, but is otherwise repairable, review historical records to determine if yoke is acceptable for special repair by an approved service facility. Yoke shall be considered unacceptable for repair if it has indeterminable history or a conditional inspection for overspeed, overtorque, hard landing, or sudden stoppage.

• If yoke is determined to be acceptable for special repair, the following information is required by the approved service facility along with the yoke:

  • Complete historical records of yoke.

  • A repair order attesting yoke has no history, which would render it unacceptable.

Pitch Horn Trunnion Bearings

• Inspect pitch horn trunnion bearings for axial looseness not to exceed 0.020 inch (0.51 mm). No radial play permitted. Purge lubricate trunnion with Grease .

Tension-Torsion Straps

Inspect tension-torsion straps for wire strand failures and for damage as follows:

• A total of 25 broken wires (50 loose ends) protruding through urethane coating of any one of the eight outside corners is cause for rejection. A total of 400 loose ends found over the entire strap surface is cause for rejection.

• Strap bulge in excess of 0.06 inch (1.5 mm) outside the normal straight contour is cause for rejection. A bulging of strap cross-section in any area from ends of strap to 3.5 inches (89 mm) inboard is normal and not cause for rejection.

• Cracks in urethane coating are acceptable providing wires are not exposed.

• Delamination of urethane coating from the bushings is acceptable. Delamination in any other area is cause for rejection.

• A permanent set in twist may occur and is not cause for rejection.

• Strap stiffness can vary when flexed in an unloaded condition and is not cause for rejection.

• Displacement of urethane wedges between bushings and inner surfaces of wire bundle is cause for rejection.

• Cracks in strap bushings are cause for rejection. Inspect using a 10X magnifying glass.

• Inspect bushings for fretting corrosion. A maximum of 0.005 inch (0.127 mm) in depth for 25% total area is allowed on bushing flange surfaces. A maximum of 0.002 inch (0.050 mm) axial scoring in depth is allowed for 1/4 of total bushing bore surfaces. No circumferential scoring is allowed.

Replace tension-torsion straps exceeding previous limits.

Requirements After Job Completion

Required Conditions

• Do a Non-Destructive Inspection (NDI) of the applicable parts.
• Refer to the repair section for the applicable repair procedures.