FAA Aviation Mechanic Airframe (AMA)Airframe StructuresMedium
A technician is servicing an air/oil (oleo pneumatic) shock strut that must be drained and recharged after a seal replacement. What is the correct general procedure for recharging the strut?
- AAdd fluid only; oleo struts do not require a separate air/nitrogen charge
- BCharge the strut with nitrogen to full pressure first, then add hydraulic fluid through the air valve
- CAdd fluid and nitrogen simultaneously while the strut is at mid-extension
- DFully compress the strut, remove the air valve, add fluid, fully extend the strut, then charge with nitrogen to the specified pressure
Show answer & explanationAnswer & explanation
Correct answer: D. Fully compress the strut, remove the air valve, add fluid, fully extend the strut, then charge with nitrogen to the specified pressure
The correct procedure is to fully compress the strut to expel trapped air, add the specified hydraulic fluid, then fully extend the strut and charge it with nitrogen (or dry air) to the manufacturer's specified pressure, ensuring proper fluid level and pressure without trapped air.
Why the other options are wrong
- A. Oleo struts require both hydraulic fluid for damping and gas pressure for spring action.
- B. Charging with air before adding fluid would trap air and prevent proper fluid fill.
- C. Simultaneous filling at mid-extension does not allow proper venting of trapped air.
Oleo Strut Servicing
An air/oil shock strut is serviced by fully compressing it to add fluid, then fully extending it before charging with nitrogen or dry air to the specified pressure.
- Combines hydraulic fluid for damping and gas for spring action
- Compress strut fully first to add fluid and remove trapped air
- Extend fully before charging with nitrogen to correct pressure
- Correct extension length verifies proper servicing
Memory trick: Squeeze then stretch: compress for fluid, extend for air.