MS28775-011 – Military Standard Synthetic Rubber O-Ring Packing
Available now through the AirParts Aero marketplace.
Overview Section
The MS28775-011 is a high-performance Synthetic Rubber O-Ring Packing manufactured to strict Military Standards (MS).1 This O-ring is the primary sealing solution for aircraft hydraulic systems utilizing MIL-PRF-5606 (mineral-based) or MIL-PRF-83282 (synthetic hydrocarbon) hydraulic fluids.
Designed specifically for static and dynamic applications, the MS28775 series features a specialized Nitrile (Buna-N) compound that provides excellent resistance to "compression set" and maintains seal integrity across a wide temperature range.2 This O-ring is a critical component for preventing high-pressure fluid leaks in actuators, valves, and landing gear struts across the Textron Aviation (Cessna and Beechcraft) fleet.
Key Features Section
MIL-H-5606 Compatibility: Formulated specifically for use with "red oil" hydraulic fluids, ensuring the rubber does not swell, shrink, or degrade when submerged.
Dual-Purpose Design: Engineered for both Static (non-moving) seals and Dynamic (reciprocating) applications like piston rods and valve stems.
Wide Temperature Operating Range: Maintains flexibility and sealing force from -65°F to +275°F (-54°C to +135°C), critical for aircraft transitioning from high-altitude cold to engine-compartment heat.
Textron OEM Grade: Sourced to meet the quality control requirements of Cessna and Beechcraft airframes, ensuring exact dimensional tolerances.
Superior Extrusion Resistance: The 70-Durometer hardness provides a balance of elasticity and toughness, preventing the O-ring from being "nibbled" or extruded into gap clearances under pressure.
Standardized Sizing: Manufactured to the -011 size specification, ensuring a perfect fit in standard aerospace gland dimensions.
Technical Specifications Section
| Specification | Detail |
| Part Number | MS28775-011 |
| Material | Nitrile (Buna-N) Synthetic Rubber |
| Hardness | 70 Durometer (Shore A) |
| Inside Diameter (ID) | 0.301 inches (Nominal) |
| Cross Section (W) | 0.070 inches (Nominal) |
| Fluid Compatibility | MIL-PRF-5606, MIL-PRF-83282, MIL-PRF-6083 |
| Military Standard | MS28775 (Supersedes AN6227 series) |
| Color | Black (Often with a blue/white dot or stripe for identification) |
Aircraft Compatibility Section
The MS28775-011 is a high-utilization seal found in numerous systems across the AirParts Aero inventory:
Cessna Single-Engine: Used in brake master cylinders and caliper assemblies for the Cessna 172, 182, and 206.
Beechcraft King Air: Found in hydraulic landing gear actuators and nose-gear steering cylinders for the 90, 200, and 300 series.
Cessna Citation: Utilized in various hydraulic manifold valves and secondary flight control actuators.
General Aviation: A standard seal for fuel strainers (gascolators) and oil filter adapters on many Lycoming and Continental engines.
Technical Applications & Safety
The MS28775-011 is a pressure-energized seal. In a hydraulic gland, the fluid pressure forces the O-ring against the side of the groove and the mating surface, creating a tighter seal as pressure increases.
Safety Warning: Never use MS28775 O-rings with Skydrol (Phosphate Ester) fluids. The Nitrile material will swell and disintegrate rapidly if exposed to Skydrol, leading to total system failure. For Skydrol systems, an Ethylene Propylene (EPR) O-ring (such as the AS3582 or NAS1613 series) must be used. Always verify the hydraulic fluid type by color: Red = Nitrile OK; Purple = Skydrol Only.
Technical Engineering Insight
The engineering value of the MS28775-011 lies in its Compression Set Resistance. Unlike industrial O-rings, the MS28775 is tested to ensure that after being compressed for thousands of hours at high temperatures, it will "spring back" to its original shape. This "memory" is what prevents leaks during "cold-soak" conditions (when an aircraft sits overnight in freezing temperatures and the metal components shrink).
By choosing the genuine Military Standard O-ring through AirParts Aero, you ensure that the surface finish of the rubber is free from "parting lines" or mold flash that can create microscopic leak paths. This is particularly vital in Dynamic Seals, where any surface imperfection can score a hydraulic piston rod, leading to a much more expensive repair.
Installation & Maintenance Addendum
Lubrication: Always lubricate the O-ring with the system fluid (e.g., clean MIL-H-5606) before installation to prevent "spiral failure" or "twisting" during assembly.
Tool Safety: Use only plastic or brass O-ring picks for removal. Steel tools can scratch the aluminum gland surfaces, creating a permanent leak path that a new O-ring cannot seal.
Shelf Life: Check the "Cure Date" on the packaging. MS28775 O-rings have a finite shelf life (typically 15 years from the cure date) and should be discarded if the rubber feels stiff or shows signs of "crazing."
*** TEXTRON SPECIFIC NOTES - PREFERRED ALTERNATE FOR BEECH MODELS - M83461/1-011 ***