3024973 - Textron Aviation OEM Coupling

3024973 – Textron Aviation OEM Starter-Generator Shear Coupling

Available now on the Airparts.aero Marketplace.

Overview

The 3024973 is a flight-critical, genuine Textron Aviation Original Equipment Manufacturer (OEM) shear coupling, designed for the starter-generator drive pad on various Cessna Citation jet aircraft. This is not a simple shaft adapter; it is a precisely engineered "mechanical fuse" that serves as the primary protection for the engine's high-speed accessory gearbox. Its sole function is to transmit torque from the gearbox to the starter-generator during normal operation, and to sacrificially fail in a predictable manner in the event of an accessory failure.

Should the starter-generator seize or experience a severe over-torque event, this coupling is designed to shear at a predetermined torque value. This action cleanly disconnects the failed accessory from the drive train, preventing the transfer of catastrophic forces back into the multi-million-dollar engine gearbox. As a genuine OEM part, its material properties and shear strength are guaranteed to meet the aircraft's type-certified design specifications.

Key Features

• Genuine Textron Aviation OEM Part: Guarantees the component is manufactured and tested to the exact material specifications and shear strength required by the engine and airframe designer.

• Engine Gearbox Protection: Engineered as a sacrificial mechanical fuse to protect the high-speed accessory gearbox from catastrophic damage in the event of an accessory seizure.

• Designed-to-Shear Neck: Features a precisely machined neck-down section with a specific diameter and surface finish, engineered to fail cleanly when a specific over-torque limit is reached.

• High-Strength Alloy Steel: Forged from a premium steel alloy and subjected to a rigorous heat treatment process to achieve the exact balance of torsional strength and predictable shear characteristics.

• Precision-Cut Splines: Features internal and external splines that are precision-machined for a perfect, low-backlash fit with the gearbox drive and the starter-generator shaft, ensuring smooth power transmission.

• Flight-Critical Component: A primary safety device for the engine's accessory drive system.

Technical Specifications

• Part Number: 3024973

• Component Type: Shear Coupling / Mechanical Fuse / Quill Shaft

• OEM Authority: Textron Aviation

• Application: Starter-Generator Drive Shaft

• Material: High-strength alloy steel, heat-treated to a specific shear strength. (Must be confirmed by OEM documentation).

• Governing Specification: Textron Aviation Engineering Drawing 3024973.

Aircraft Compatibility

This OEM shear coupling is the specified component for the starter-generator drive on numerous Cessna Citation business jet models.

• Primary Textron Aviation Platforms:

  • Cessna Citation 525 Series (CJ, CJ1, CJ2, M2)

  • Cessna Citation V, Ultra, Encore

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 and absolute authority for confirming part number eligibility.

Applications

• Sole Application: To transmit torque between the engine accessory gearbox and the starter-generator, and to provide over-torque protection for the gearbox by failing in a controlled shear event.

Why Choose 3024973?

The shear torque value of this coupling is one of the most critical engineering parameters in the entire engine accessory drive train. Only the genuine Textron Aviation OEM part is guaranteed to have been manufactured from the correct alloy and subjected to the precise heat treatment and machining processes required to ensure it will shear at the correct torque value. A non-certified part that is too strong will fail to protect the accessory gearbox, leading to catastrophic engine damage. A part that is too weak will shear prematurely, leading to an in-flight loss of the generator and potentially the engine's start capability. There is no substitute for the certified OEM part.

The 3024973 shear coupling is a classic example of "designing for failure" as a primary safety feature. Its function is governed by the principles of torsional stress and material science. The "neck" of the coupling has a precisely machined diameter, fillet radius, and surface finish. This geometry, in combination with the material's specific ultimate shear strength (a property derived from its exact alloying and heat treatment), creates a known, predictable failure point. During an over-torque event, the torsional stress in the shaft, calculated by the formula τ=Tr/J (where τ is shear stress, T is torque, r is radius, and J is the polar moment of inertia), becomes concentrated at this necked-down section. The coupling is engineered so that when the torque (T) exceeds the maximum safe limit for the accessory gearbox, the shear stress (τ) at the neck exceeds the material's ultimate shear strength. This initiates a clean, ductile shear fracture, severing the drive line before the destructive torque can be transmitted to the expensive and difficult-to-replace gearbox components.

Note: This is a flight-critical, single-event engine component. If a shear event occurs or is suspected, the coupling must be replaced and cannot be reused. A sheared coupling is an indication of a severe problem with the driven accessory (the starter-generator), which must be removed and investigated or replaced before a new coupling is installed. Installation requires correct alignment and lubrication of the splines per the aircraft maintenance manual.

Documentation

All technical data, including material and shear strength specifications, are proprietary to Textron Aviation. All installation and inspection procedures are contained within the official Maintenance Manual for the applicable Cessna Citation model. No public-facing documentation is available.