Definition
Hydraulic valves in a retractable landing gear system that control the order of mechanical events during gear extension and retraction, ensuring that gear doors and gear legs operate in the correct sequence. They prevent the gear from attempting to move while the doors are still closed, and prevent the doors from closing on partially retracted gear.
Plain English
Valves that make sure things happen in the right order when the landing gear goes up or down — doors first, then gear, then doors closed again — so nothing tries to move through something that's still in the way.
Context Anchor
Seen in discussions of retractable landing gear systems, especially gear extension and retraction with gear doors.
Derivation
‘Sequenced’ comes from the Latin sequi, meaning ‘to follow.’ A sequence is a set of things that follow one after another in order. So sequenced valves are simply valves that act in a set order rather than all at once.
Why Pilots Care
Proper sequencing avoids mechanical interference and keeps the gear system reliable during takeoff and landing.
Analogy
Think of a sequenced valve like a gate that will not open until the previous gate has opened first. It keeps the steps from happening out of order.
Intuition Check
Do not assume sequenced valves are just timers. They control the flow of fluid so the landing gear parts move in the required order.
Example Sentence 1
When the pilot selected gear down, the sequenced valves opened the gear doors first before allowing hydraulic pressure to extend the gear legs.
Example Sentence 2
During an emergency extension, the sequenced valves still ensure the doors open fully so the gear can drop into place without jamming.