S378-3 – Textron Aviation OEM Phenolic Flight Control Cable Pulley (MS24566-3B)
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Overview
The S378-3 is a flight-critical, genuine Textron Aviation (Cessna) Original Equipment Manufacturer (OEM) flight control cable pulley, conforming to the military standard MS24566-3B. This component is essential for the smooth and reliable operation of an aircraft's primary flight control system. Its function is to guide the control cables, changing their direction with minimal friction, ensuring that pilot inputs are transmitted accurately and efficiently to the control surfaces (ailerons, elevator, rudder).
Manufactured from a high-strength, fabric-reinforced phenolic thermosetting plastic, this pulley is engineered for exceptional durability, low weight, and resistance to wear. It incorporates a precision, shielded ball bearing (typically MS27640) at its center to ensure low rotational friction and a long service life. As the genuine OEM part, the S378-3 guarantees the correct dimensions, material properties, and bearing quality required for this critical, no-compromise application.
Key Features
Genuine Textron Aviation OEM Part: Guarantees the part is the factory-specified and fully certified component, ensuring correct fit, performance, and airworthiness.
MS24566 Standard Compliance: Manufactured and tested in strict accordance with the military standard for anti-friction bearing control pulleys.
Fabric-Reinforced Phenolic Body: Provides an excellent combination of high strength-to-weight ratio, impact resistance, and inherent corrosion resistance.
Low-Friction Ball Bearing: Incorporates a precision, pre-lubricated, and shielded ball bearing (typically MS27640-3) to minimize cable drag and ensure smooth control feel.
For 1/8" Control Cable: The groove profile is precisely machined to correctly guide standard 1/8-inch diameter aircraft control cable.
Flight-Critical Component: A primary component in the direct linkage between the pilot's controls and the aircraft's control surfaces.
Technical Specifications
Part Number: S378-3
Cross-Reference Standard: MS24566-3B
Component Type: Flight Control Cable Pulley
OEM Authority: Textron Aviation (Cessna)
Pulley Material: Fabric-Reinforced Phenolic Resin
Bearing: Integral MS27640-3 Shielded Ball Bearing
Nominal Outside Diameter: 2 inches
For Cable Diameter: 1/8 inch
Governing Specification: MS24566; Textron Aviation Engineering Drawing S378.
Aircraft Compatibility
The S378-3 (MS24566-3B) is a standard pulley used extensively across the Textron Aviation fleet and the wider general aviation industry.
Primary Textron Aviation Platforms:
Cessna Piston Aircraft (100, 200, 300, 400 Series)
Cessna Caravan Series
Certain applications in Cessna Citation business jets.
General Aerospace Usage: A common flight control pulley on aircraft from Piper, Beechcraft, Mooney, and many others.
Note: Verification of applicability is the absolute responsibility of the installer. The aircraft's current Illustrated Parts Catalog (IPC) for its specific serial number is the final authority for confirming part number eligibility for a specific location.
Applications
Sole Application: To guide and change the direction of primary flight control cables (aileron, elevator, rudder) within the airframe structure.
Why Choose S378-3?
The integrity of the flight control system is paramount. Worn or failed pulleys can cause stiff controls, excessive cable wear, or, in the worst case, a jammed or severed control cable. The genuine Textron OEM S378-3 guarantees that the pulley body is free from manufacturing defects, the groove profile is correct to prevent cable chafing, and most importantly, that the integral bearing is a certified, high-quality aerospace component. Using a non-certified pulley with an industrial-grade bearing introduces an unacceptable risk of bearing seizure or collapse, which could lead to a loss of flight control.
The material choice for the S378-3 pulley body, fabric-reinforced phenolic resin, is a deliberate engineering decision based on its unique combination of properties. Phenolic is a thermosetting plastic created by polymerizing phenol and formaldehyde. When reinforced with layers of woven fabric (like cotton or linen) during the molding process, the resulting composite exhibits high impact strength, excellent resistance to wear and abrasion from the steel control cable, and dimensional stability across a wide temperature range. Crucially, it is also significantly lighter than an equivalent aluminum pulley, contributing to weight savings in the flight control system. Furthermore, phenolic resin possesses excellent dielectric properties and is inherently resistant to corrosion from moisture and common aircraft fluids, ensuring a long and reliable service life in the airframe environment.
Note: This is a flight-critical component. It is a wear item and must be inspected regularly for freedom of rotation, bearing roughness, groove wear, chips, and cracks in accordance with the aircraft maintenance manual. Installation must be performed by a certified A&P mechanic. The mounting bolt must be correctly torqued, and safety wired if applicable. Ensure the cable is properly seated in the groove and that cable guards (if installed) are correctly positioned.
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 MS24566: http://quicksearch.dla.mil/qsDocDetails.aspx?ident_number=42562