GEAR SEQUENCING, PROXIMITY SENSING AND GRAVITY EXTENSION
Landing-gear movement is electrically controlled and hydraulically actuated in the supplied architecture. The gear lever requests a sequence; the landing-gear control/interface units coordinate gear and door movement using position information. Proximity detectors establish actual sensed positions rather than relying on a lever to prove extension. The main gear retract inboard and the nose gear forward. Doors associated mechanically with the gear are distinguished from the doors participating in the controlled sequence. [89, PDF pp. 2–6]
The two LGCIUs provide control and information functions. Their signals also support other aircraft systems, including flight/ground logic. A gear indication can therefore be affected by sensing or interface failure even when a physical component has moved, and an LGCIU problem can create consequences outside the WHEEL page. Compare the specific warning, individual position indications and actual sequence before deciding whether the problem is hydraulic movement, mechanical locking, sensing or control. The architecture explains why several warnings may share one interface cause. [89, PDF pp. 6–18]
Gravity extension uses a different means of releasing and lowering the gear from the normal hydraulic sequence. The source identifies the mechanical emergency-extension provision and its changes to gear/door behaviour. This is a system capability with procedural consequences; it does not guarantee that every normal door position, steering function or subsequent retraction remains available. The applicable emergency procedure and resulting status determine the retained capability. A successful down indication answers the locking question, not every question about the landing configuration. [89, PDF pp. 5, 21–22] [87, PDF p. 87]
Normal and abnormal training should retain three separate checks: lever/requested state, sequence/position indications and the capability required for the next operation. Gear down and locked does not establish brake source, anti-skid, autobrake or nosewheel steering. Those have separate supplies and controls. The reference’s speeds and inhibit thresholds are not reissued here as current Fenix limits. Use the loaded aircraft’s valid limits and failure procedure, particularly when an emergency-extension state or interface fault changes what can be expected after touchdown. [89, PDF pp. 19–22] [87, PDF pp. 87–92]