O-Rings for Aerospace Applications
AS568-standard sealing solutions for hydraulic systems, fuel systems and aircraft maintenance — in Skydrol-compatible FKM and military-specification compounds.
Overview
Aerospace sealing demands the most exacting dimensional tolerances, material certifications and performance consistency of any industry. O-rings in aircraft hydraulic systems, fuel controls, engine assemblies and landing gear must perform across extreme temperature ranges — from -54°C at altitude to +200°C near engine components — while maintaining sealing integrity through millions of pressure cycles.
AS568 was originally developed for the US aerospace industry and remains the defining O-ring size standard for aerospace applications globally. Military specifications (MIL-P-5315, MIL-R-83485) define material and quality requirements for US military and many commercial aerospace programmes.
Recommended Materials
FKM 75 Shore A
Hydraulic systems using phosphate ester fluids (Skydrol 500B-4, Skydrol LD-4, Skydrol 5), fuel system O-rings, engine accessory seals
Temp: -20°C to +200°C
Note: Required for all Skydrol hydraulic systems — NBR fails rapidly in phosphate ester fluids
NBR 70 Shore A
Mineral oil hydraulic systems, fuel cells, ground support equipment
Temp: -40°C to +120°C
Note: AS568 standard NBR for non-Skydrol applications
Silicone VMQ
Avionics cooling seals, altitude pressure systems, low-temperature static seals
Temp: -60°C to +230°C
Note: For wide temperature range static sealing — not suitable for dynamic hydraulic service
FFKM
Engine hot section seals, fuel nozzle seals, high-temperature high-pressure critical sealing positions
Temp: -15°C to +325°C
Note: Specified where FKM temperature limits are exceeded
Typical Applications
- Fuel system seals
- Hydraulic actuator seals
- Engine seals
- Landing gear seals
- Oxygen system seals
- Avionics cooling seals
- Environmental control seals
- APU seals
Relevant Standards
Frequently Asked Questions - Aerospace
What is Skydrol and why does it require FKM O-rings?
Skydrol is a fire-resistant phosphate ester hydraulic fluid used in commercial aircraft. Phosphate ester fluids are incompatible with NBR rubber — they cause rapid swelling and degradation. FKM is the correct O-ring material for all Skydrol-based hydraulic systems (Skydrol 500B-4, LD-4, 5, and equivalent fluids from other manufacturers).
What military specification covers O-rings?
MIL-P-5315 covers rubber O-rings for US military hydraulic fluid applications. MIL-R-83485 covers fluorocarbon rubber O-rings. AS568 dash numbers are used with these specifications. Commercial aviation typically follows SAE AS568 with material specified per aircraft maintenance manual requirements.
Can you supply O-rings with aerospace material certificates?
Yes. We supply O-rings with full material traceability, hardness test reports and dimensional certificates. For specific military or OEM certification requirements, contact us with the specification and we will confirm compliance capability.
What O-ring material is used in aircraft fuel systems?
Fuel system O-rings depend on the fuel type. For jet fuel (Jet A, JP-8), FKM is preferred for high-temperature locations and FKM or NBR for ambient-temperature fittings. For avgas (aviation gasoline), NBR is standard. Consult the aircraft maintenance manual for approved materials at specific locations.