How to Service Aircraft Main Struts

Aircraft struts absorb shock with a cushion of nitrogen and hydraulic fluid.

An aircraft landing can create a substantial impact at the landing gear. This impact is absorbed by the aircraft struts. Struts are partially filled with hydraulic fluid and then serviced with nitrogen. You'll need to consult the aircraft service manuals or placards attached to the struts to find the exact type of hydraulic fluid to use and the required nitrogen pressure. The procedures for servicing aircraft struts will vary slightly depending on the particular type of aircraft involved, but the basic procedure is standard.

Things You'll Need

• Aircraft jacks
• Wrench
• Hydraulic fluid
• Bucket
• 2 foot rubber hose
• Hose clamp
• 2 quart container
• Pressurized nitrogen

Instructions

Fluid Level

1. Jack the aircraft.

2. Remove the valve cap from the strut and press the valve core to release the nitrogen charge from the strut.

3. Remove the valve core with a wrench.

4. Attach the rubber hose to the threaded section that holds the valve core with the hose clamp.

5. Fill the 2 quart container with the correct hydraulic fluid for the strut and lace the other end of the rubber hose in it. Cover the container with a rag to control any spills.

6. Slowly lift the strut by hand or with an additional jack to release any additional air from it. Lower the strut again to suck the hydraulic fluid from the bucket into the strut. Continue to slowly raise and lower the strut until you cannot hear air bubbles from the container when the strut is completely compressed.

Adding Nitrogen

1. Remove the rubber hose and reinsert the valve core while the strut is still completely compressed.

2. Lower the strut from its compressed position.

3. Use a pressurized nitrogen source to inflate the strut to the proper pressure for your aircraft.

Tips & Warnings

• If you're servicing very large aircraft, might need a larger container for hydraulic fluid as well as a longer rubber hose.

References

• "Aviation Week: Landing Gear Maintenance Tips"
• AVweb: The Savvy Aviator #31: Know Your Oleo
• Federal Aviation Administration: Regulatory and Guidance Library-Aircraft Systems and Components