FAA Aviation Mechanic Airframe (AMA)Landing Gear SystemsHard
During landing gear retraction on a hydraulic-actuated system, a technician notes that the gear doors must fully open before the main gear strut begins retracting. Which component ensures this timing?
- APriority (sequence) valve
- BShuttle valve
- CSelector valve
- DRestrictor check valve
Show answer & explanationAnswer & explanation
Correct answer: A. Priority (sequence) valve
A priority or sequence valve controls the order of hydraulic actuation, ensuring gear doors open fully before the gear itself begins to retract (or that the gear is stowed before doors close), preventing structural interference.
Why the other options are wrong
- B. A shuttle valve selects between two pressure sources (e.g., normal and emergency), not sequencing.
- C. The selector valve directs fluid to the up or down side of the system but doesn't control timing between actuators.
- D. A restrictor check valve limits flow rate/speed in one direction, not sequencing between separate actuators.
Sequence (Priority) Valve
A hydraulic valve that controls the order of operation between two actuators, such as gear doors and gear struts, during retraction/extension.
- Ensures doors open before gear retracts
- Prevents structural interference between doors and gear
- Common in complex retractable gear hydraulic systems
Memory trick: Sequence valve is the traffic cop: doors first, then gear