Summary of Aircraft Instruments and Systems

## Introduction Aircraft warning and stall systems are critical for flight safety. They alert pilots about configuration problems and impending aerodynamic stalls so corrective action can be taken promptly. This guide explains how common warning horns and stick shakers work, when they activate, and how pilots use their cues during approach and stall avoidance. ## Landing-gear Warning Horn ### What triggers the warning horn? > **Definition:** The landing-gear warning horn is an auditory alert that notifies the flight crew when the landing configuration is unsafe for approach or landing. - The warning horn will sound when the throttles are pulled back (reducing engine power for landing) if **any landing gear is not down and locked**. - Its purpose is to prevent a landing with incomplete gear extension which could cause gear-up or partial-gear landings and significant aircraft damage or injury. ### How it works (conceptual breakdown) 1. Sensing: Each main and nose gear has down-and-locked switches that provide discrete indications: "down and locked" or "not down/locked." 2. Logic: A small logic circuit or the landing-gear system controller monitors throttle/engine power settings and gear switch states. 3. Activation: If throttles are retarded below a certain threshold (indicating landing configuration) while any gear switch is not in the down-and-locked position, the horn is energized. 4. Pilot response: The crew must either advance power and execute a go-around or confirm and extend/lock the gear before continuing the approach. ### Practical example - On final approach the pilot reduces thrust to set approach speed. If the nose gear failed to extend and the other gear show down-and-locked, the warning horn sounds. The correct action: apply power, climb to safe altitude, troubleshoot and land with proper gear extension or declare emergency if necessary. ## Stick Shaker (Artificial Stall Warning) > **Definition:** A stick shaker is a mechanical or electromechanical device that rapidly vibrates the control column to provide an unmistakable tactile warning of an approaching aerodynamic stall. ### Purpose and function - The stick shaker provides an **artificial stall warning** to the pilot before the aircraft reaches a full aerodynamic stall. - It is driven by the stall protection system, which monitors angle-of-attack (AOA) sensors and other parameters. - When AOA approaches a preset threshold (near the critical AOA), the stick shaker activates to prompt immediate pilot correction. ### Pilot action when the stick shaker activates - Immediate reduction of angle of attack: push the control column forward to reduce AOA. - Add appropriate power to arrest descent and regain safe flying speed. - Reconfigure (flaps, gear) as required by the aircraft operating procedures to exit the stall regime. ### Real-world application - The stick shaker is common on transport-category aircraft and some high-performance light aircraft where the natural pre-stall buffet or buffet onset may be mild or late. - It provides a tactile cue that is hard to ignore, especially if visual or aural cues are missed in high workload situations. ## Comparison: Landing Gear Horn vs Stick Shaker | Feature | Landing-Gear Warning Horn | Stick Shaker | |---|---:|---:| | Purpose | Alert gear not down/locked during landing configuration | Alert imminent aerodynamic stall (high AOA) | Trigger condition | Throttles pulled back or landing configuration logic + gear not down | AOA reaches a preset threshold near critical AOA | Cue type | Audible horn | Tactile vibration of control column (often with aural stall warning too) | Typical pilot response | Advance power/go-around or extend gear | Reduce AOA, add power, follow stall recovery procedure ## Practical checklist items (bulleted) - Before reducing power on approach: verify gear down-and-locked indications. - If landing-gear horn sounds: confirm gear status, apply power, climb to safe altitude, troublesho