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MS9386-015 – Textron Aviation OEM Preformed O-Ring (AMS 7276)
Available now through the AirParts Aero marketplace.
Overview Section
The MS9386-015 is a high-performance Fluorocarbon (FKM) O-ring designed for critical sealing in high-temperature aerospace environments. Manufactured to meet the AMS 7276 material specification, this O-ring is a staple in Textron Aviation (Cessna and Beechcraft) airframes and powerplants.
Engineered specifically for "hot-side" applications, the MS9386-015 is designed to remain flexible and chemically stable when exposed to aggressive synthetic lubricants and turbine fuels. Unlike standard Nitrile seals, the Fluorocarbon compound used in this part resists hardening and "set" when subjected to the intense thermal cycling of turbine engine operations.
Key Features Section
AMS 7276 Material (Viton/FKM): Provides superior resistance to heat, ozone, and chemical degradation. It is the industry standard for high-performance aviation fluid systems.
Wide Temperature Range: Operates effectively in environments from -10°F to +400°F (-23°C to +204°C), maintaining a leak-proof seal during high-altitude cold-soaks and high-power engine runs.
Chemical Compatibility: Highly resistant to MIL-PRF-23699 synthetic turbine oils, Jet A/JP-8 fuel, and standard petroleum-based hydraulic fluids.
Precision Size (-015): Part of the small-diameter "000" series, providing a precise fit for small fluid ports, engine accessories, and instrument interfaces.
Reduced Compression Set: Formulated to retain its original shape and "spring-back" force even after years of being compressed in a metal gland.
OEM Traceability: Sourced as a Textron Aviation OEM part, ensuring the highest level of quality control and material purity required for certified aircraft.
Technical Specifications Section
| Specification | Detail |
| Part Number | MS9386-015 |
| Material Standard | AMS 7276 (Fluorocarbon / FKM) |
| Inside Diameter (ID) | 0.551 in (Nominal) |
| Cross-Section (W) | 0.070 in (Nominal) |
| Hardness | 70-80 Shore A Durometer |
| Color | Black |
| Primary Application | High-Temp Static/Dynamic Sealing |
Aircraft Compatibility Section
The MS9386-015 is a ubiquitous seal found across the Textron Aviation fleet:
Beechcraft King Air Series: Used in engine oil lines, fuel pump interfaces, and bleed air system components.
Cessna Citation Series: Found in various airframe hydraulic fittings and engine accessory mounting points for Pratt & Whitney and Williams engines.
Cessna Caravan (208): Integral to the PT6A engine oil system and fuel delivery components.
Piston Fleet (Cessna 172/182/206): Frequently utilized in high-heat areas like oil filter adapters and turbocharger oil supply lines.
Technical Applications & Safety
O-rings function by being mechanically "squeezed" within a metal groove (gland).1 The MS9386-015 relies on this compression to create a high-pressure barrier.
Safety Warning: Do Not Intermix Materials. While the MS9386-015 (Fluorocarbon) may look identical to the MS29513 (Nitrile) O-ring, they are chemically distinct. If a Nitrile O-ring is mistakenly installed in an AMS 7276 application, it will turn brittle and shatter under heat, leading to a sudden loss of oil or fuel pressure. Always verify the part number on the individual sealed package before installation.
Technical Engineering Insight
The engineering value of the MS9386-015 lies in its Molecular Stability. In the presence of "Type II" synthetic turbine oils, standard rubber compounds undergo a process called "swell and soften," which eventually leads to the seal extruding out of its gap. The AMS 7276 compound features a highly fluorinated backbone that prevents these oil molecules from penetrating the elastomer. This ensures the seal maintains its Durometer (Hardness) throughout its service life, preventing "nibbling" failures where the edge of the O-ring gets chewed up by system pressure.
Installation & Maintenance Addendum
Gland Inspection: Before installing a new MS9386-015, use a 10x magnifying glass to inspect the metal gland for scratches or "pitting." A scratch only 0.001" deep can create a leak path that the O-ring cannot bridge.
Clean Installation: Never use a metal pick to seat the O-ring. Use plastic or wooden tools to avoid damaging the AMS 7276 material.
Shelf Life: While Fluorocarbon has an excellent shelf life, Textron typically recommends replacing seals that are more than 15 years past their cure date to ensure maximum reliability.
