259N04 - Textron Aviation OEM Nylon Fitting Seal Insert

259N04 – Textron Aviation OEM Nylon Sleeve for -4 Instrument Fittings

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Overview

The 259N04 is a genuine Textron Aviation Original Equipment Manufacturer (OEM) nylon sealing sleeve, engineered for use in flareless tube fittings within low-pressure aircraft systems. This is a flight-critical component, most commonly found in pitot-static and pneumatic instrument line connections. Its purpose is to create a positive, leak-free seal on 1/4-inch (-4 size) aluminum tubing without the need for flaring the tube end.

This is not a simple washer or O-ring; it is a precisely dimensioned ferrule that functions via compression. When the fitting nut is tightened, the 259N04 sleeve is compressed against the tubing, causing the nylon material to deform and create an airtight grip and seal. As the genuine OEM part, it is manufactured from the specific grade and durometer of nylon required to ensure a reliable seal that is essential for the accuracy of primary flight instruments.

Key Features

• Genuine Textron Aviation OEM Part: Guarantees the part is fabricated to the exact Textron engineering drawing for material composition, dimensions, and performance, ensuring a perfect seal.

• Nylon Compression Sleeve Design: The engineered nylon material is designed to deform under compression to create a strong mechanical grip and a positive, gas-tight seal on the outside of the tube.

• Creates a Flareless Seal: Eliminates the need for a 37-degree flaring tool and the potential for cracked flares, simplifying the assembly of instrument lines.

• For -4 (1/4") Tubing: Specifically sized for a precise interference fit on standard 1/4-inch outside diameter aluminum tubing.

• For Pitot-Static & Pneumatic Systems: The nylon material and low-pressure design make it the ideal component for instrument air lines, but unsuitable for high-pressure hydraulic or high-temperature fluid systems.

• Single-Use Component: Designed to be plastically deformed during its one and only installation to ensure a perfect, reliable seal.

Technical Specifications

• Part Number: 259N04

• Component Type: Flareless Fitting Sealing Sleeve / Ferrule / Packing

• OEM Authority: Textron Aviation

• For Tube Outside Diameter: 1/4 inch (-4 size)

• Material: Nylon

• System Application: Low-Pressure Pneumatic, Pitot-Static Systems, Instrument and Vent Lines.

• Governing Specification: Textron Aviation Engineering Drawing 259N04.

Aircraft Compatibility

This OEM sealing sleeve is the specified component for instrument line fittings on a vast range of Textron Aviation aircraft.

• Primary Textron Aviation Platforms:

  • Cessna Piston Aircraft (100 and 200 Series, e.g., 172, 182, 210)

  • Cessna Caravan Series

  • Certain applications in Cessna Citation business jets.

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 create a positive seal in flareless, compression-style tube fittings used for connecting:

  • Pitot and static air lines to the airspeed indicator, altimeter, and vertical speed indicator.

  • Pressure or vacuum lines for gyroscopic flight instruments.

  • Other low-pressure pneumatic instrument and sensing lines.

Why Choose 259N04?

The accuracy of an aircraft's primary flight instruments is absolutely critical for flight safety, especially in instrument meteorological conditions (IMC). A leak in the pitot-static system, caused by a faulty or reused fitting sleeve, will result in dangerously erroneous airspeed, altitude, and vertical speed indications. Only the genuine Textron Aviation OEM 259N04 sleeve is guaranteed to be made from the correct, certified nylon compound and dimensioned to the precise tolerances required to create a reliable, leak-free seal in these flight-critical systems.

The 259N04 is the sealing element in a single-ferrule flareless compression fitting. The engineering principle of this joint is the controlled plastic deformation of the nylon sleeve to create a seal and mechanical grip. As the fitting's nut is tightened, it drives the sleeve forward along the tube into a conical or tapered seat within the fitting body. This interaction of tapered surfaces applies a powerful axial and radial force to the sleeve. This force causes the relatively soft nylon to compress radially inward, "biting" into the outer surface of the aluminum tubing to create a strong, vibration-resistant mechanical grip. Simultaneously, the nose of the sleeve is forced into the tapered seat, creating a positive, gas-tight seal between the sleeve and the fitting body, while the inner diameter of the sleeve seals against the tube. This dual-sealing action makes the flareless compression fitting a simple and highly reliable method for joining low-pressure instrument lines.

Note: This is a flight-critical, single-use component. A new 259N04 sleeve must be used every time the fitting is disassembled and reassembled. Reusing a deformed sleeve will not result in a reliable, leak-free seal. Installation must be performed by a certified A&P mechanic in accordance with the aircraft maintenance manual. The tubing must be clean, round, and free of scratches, and it must be fully seated in the fitting before the nut is tightened.

Documentation

All technical data, installation procedures, and torque specifications for the 259N04 sleeve are proprietary to Textron Aviation. This information is contained within the official Maintenance Manual and Standard Practices documents for the applicable aircraft model. No public-facing documentation is available.