MS9581-09 - Textron Aviation OEM Keyed Lock Washer

MS9581-09 – Textron Aviation OEM Spindle Key Washer (7/8")

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Overview

The MS9581-09 is a flight-critical, positive locking device that holds dual authority as a component built to a precise Military Standard and as a genuine Textron Aviation Original Equipment Manufacturer (OEM) part. This is not a standard washer; it is a keyed lock washer specifically designed to mechanically secure large spindle or axle nuts against rotation. Its most common application is locking the wheel bearing retainer nut on main and nose landing gear assemblies.

Manufactured from a high-strength yet ductile cadmium-plated carbon steel, the washer features an inner key that fits into a keyway on the axle to prevent the washer itself from rotating. After the axle nut is torqued to set the wheel bearing preload, one of the outer tabs is bent up against a flat on the nut, creating an infallible, physical lock. As the certified Textron OEM part, it guarantees the material properties and dimensional tolerances required for this critical safety-of-flight application.

Key Features

• Textron Aviation OEM Certified: Guarantees the part is the factory-approved, fully traceable component for the Textron Aviation family of aircraft.

• Positive Mechanical Lock: Provides a physical barrier that prevents the axle nut from rotating, a more secure method than friction-based locking for critical rotating assemblies.

• Internal Key for Anti-Rotation: A tab on the inner diameter engages with a keyway on the spindle or axle, preventing the washer from turning with the nut.

• Bendable Locking Tabs: The outer diameter features multiple tabs, allowing one to be bent up against the nut for a secure lock regardless of the nut's final rotational position.

• Cadmium Plated Carbon Steel: Manufactured from a specific steel alloy that is strong enough to resist shear forces, yet ductile enough to be bent into its locking position without fracturing.

• MS9581 Standard Compliance: Meets all dimensional, material, and quality requirements of the military standard for spindle key washers.

Technical Specifications

• Part Number: MS9581-09

• Component Type: Key Washer / Spindle Lock Washer

• OEM Authority: Textron Aviation

• Governing Specification: MS9581

• Material: Carbon Steel

• Finish: Cadmium Plated per QQ-P-416

• For Spindle Thread Size: 7/8-14 UNF

• Inner Diameter: 0.885 inches

Aircraft Compatibility

As a Textron Aviation OEM part, this key washer is specified for the landing gear assemblies of numerous aircraft in their fleet. The underlying MS standard makes it common across the industry.

• Primary Textron Aviation Platforms:

  • Cessna Citation Series Business Jets

  • Beechcraft King Air Series

  • Beechcraft Baron and Bonanza

• General Aerospace Usage: Used on any aircraft landing gear axle or other spindle application that calls for an MS9581-09 lock washer.

Note: Verification of applicability is the responsibility of the installer. Always consult the current version of the aircraft's Illustrated Parts Catalog (IPC) and maintenance manual to confirm part number eligibility for a specific landing gear assembly.

Applications

• Sole Application: To provide a positive, mechanical lock for spindle nuts, most commonly on main and nose landing gear axles to secure the wheel and bearing assembly and maintain correct bearing preload.

Why Choose this MS9581-09?

The safe operation of an aircraft's landing gear is non-negotiable. The failure of a wheel bearing assembly due to an improperly secured axle nut can be catastrophic, potentially leading to a wheel departing the aircraft. The MS9581-09 key washer is the specified safety device to prevent this. Only the genuine Textron OEM part is guaranteed to have the correct material properties (strength and ductility) and precise dimensions for this critical, high-stress application. The use of a non-certified part would create an unacceptable risk of landing gear failure.

The engineering principle behind the use of a key washer like the MS9581-09 in a wheel bearing application is the necessity of a positive lock to maintain a precise preload setting, rather than a friction lock designed to maintain a high clamp load. The axle nut on a tapered roller bearing is not tightened to a high torque value; instead, it is torqued through a specific procedure (e.g., torque to seat the bearings, then back off and re-torque to a much lower value) to achieve a minute amount of bearing end-play or a light preload. This setting is critical for the longevity of the bearings. A prevailing torque locknut is unsuitable as its friction can interfere with accurately feeling the bearing preload. The key washer allows the nut to be precisely positioned and then physically locked in that position by bending the tab. This ensures the critical bearing preload setting is maintained, preventing bearing overheating (too tight) or wheel wobble and brinelling (too loose).

Note: This is a flight-critical, single-use hardware component. A new key washer must be used every time the axle nut is removed and re-installed. The tabs are not designed to be bent more than once. Installation must be performed by a certified A&P mechanic in strict accordance with the aircraft maintenance manual, which provides the detailed, multi-step procedure for torquing the axle nut to set the correct bearing preload before the lock tab is bent.

Documentation

The military standard governing this part is publicly available through the Department of Defense ASSIST database. OEM-specific application and installation data is contained within the Textron Aviation maintenance manuals.

• ASSIST Document Summary Page for MS9581: http://quicksearch.dla.mil/qsDocDetails.aspx?ident_number=38558