The aviation industry demands the highest technical standards to ensure flight safety and operational efficiency. Lubricants and greases play a vital role in meeting these standards, serving critical functions across engines, powertrains, hydraulic systems, and landing gear. Modern aircraft and helicopter systems feature highly complex structures and advanced engineering solutions. Their performance, safety, and durability depend on the implementation of precise lubrication strategies. Beyond reducing friction, aviation lubricants also provide essential benefits such as cooling, corrosion protection, contaminant control, and seal compatibility.
Lubricants used in aviation can be broadly categorized into three main groups:
- Engine Oils (Used in both piston and turbine engines)
- Hydraulic System Oils (Applied in systems such as flight controls and landing gear)
- Greases (Bearings, joints, hinges, transmission components)
Additionally, specialty oils, such as those integrated with coolants or formulated for rotor gearbox systems in helicopters, are tailored to meet specific operational and environmental demands.
Engine Oils
- Turbine Engine Oils
Lubricants used in jet and turboshaft engines are typically synthetic ester-based, engineered for high thermal resistance and performance across a wide temperature range, from −54°C to +204°C. These oils are formulated to meet the MIL-PRF-23699 specification. Their high oxidation stability and chemical resilience support long-duration operations under extreme conditions.
- Piston Engine Oils
Piston engines, commonly found in general aviation, especially in light and training aircraft, use oils that are either mineral-based or synthetic. These lubricants typically fall within high viscosity grades such as SAE 50 and SAE 100, offering optimal performance between 80°C and 115°C, with viscosity stability at 100°C and thermal resistance up to 200°C. Formulated with antioxidant, detergent, and dispersant additives, these oils help prevent carbon buildup, maintain engine cleanliness, and extend operational life.
Hydraulic System Oils
Aviation hydraulic system oils serve as power transmission media, enabling the precise and reliable movement of critical components such as landing gear, flight control surfaces, brake mechanisms, and rotor systems in both aircraft and helicopters.
These specialized fluids, typically formulated with high-viscosity index synthetic base oils, are engineered to remain stable across a wide temperature range. In addition to transmitting force, they perform multiple essential functions such as reducing friction, providing sealing, cooling the system, and protecting metal surfaces against corrosion.
Phosphate ester-based hydraulic oils, noted for their fire resistance, are particularly preferred in high-temperature systems, while mineral-based versions are ideal for low-temperature performance. Compliance with military standards such as MIL-PRF-5606 and MIL-PRF-83282 and chemical compatibility with elastomers are critical factors in flight safety.
Greases
Aviation greases are preferred to ensure the safe and long-lasting operation of high-load components such as helicopter rotor heads, landing gear mechanisms, flap systems, nose wheel steering systems, and bearings.
These greases are generally synthetic ester- or perfluoropolyether (PFPE)-based and formulated with thickeners such as lithium complex, bentonite, polyurea, and organic clays. These products, which maintain stability over a wide temperature range (−73°C to +177°C), offer high resistance to water and chemicals. Low evaporation rate and mechanical stability are critical performance criteria in aviation applications. Compliance with military specifications such as MIL-PRF-23827 and MIL-PRF-81322 is a fundamental requirement for flight safety.
Helicopter Gearbox Oils
In helicopters, special oils containing Extreme Pressure (EP) additives are used in the gearboxes that connect the main rotor and tail rotor systems, providing resistance to high loads and impact stresses.
These oils typically feature polyalphaolefin (PAO) or ester-based synthetic formulations, offering stability against sudden temperature spikes. Anti-foam and anti-corrosion additives are essential for ensuring the longevity and safe operation of these systems. The products used generally comply with military specifications such as DEF STAN 91-100, or meet OEM approvals from manufacturers like Bell and Airbus Helicopters.
Because rotor systems, transmission cases, and swashplate mechanisms operate under constantly changing loads and vibration, the lubricants must exhibit properties such as high film strength, vibration stability, low-temperature fluidity, and extended service life.
Oils and greases used in aviation are invisible yet indispensable engineering components, critical to flight safety, system durability, maintenance costs, and operational efficiency. Matching these advanced formulations with the correct systems is fundamental to ensuring optimal performance and safety. Therefore, the selection process must consider not only technical specifications but also OEM approvals, field performance, maintenance intervals, and sustainability criteria.
Thanks to ongoing technological advancements, the role of lubricants is expanding, reshaping their function to minimize environmental impact while enhancing reliability across increasingly complex aviation platforms.
