Take-off Configuration Warning (TOCW): Trigger Logic and Crew Checks

Overview

The Take-off Configuration Warning (TOCW) system is a critical safety mechanism designed to prevent an aircraft from attempting a takeoff in an unsafe configuration.

Regulations (CS 25.703)

Regulations mandate that large transport aircraft must be equipped with a system that provides an aural warning automatically during the initial portion of the takeoff roll.

• Timing: The alert must trigger when throttles are advanced (applied takeoff power) while on the ground.
• Indication: The minimum requirement is an Aural alert (e.g., Siren, Horn, or Voice "CONFIG FLAPS"). Many aircraft also provide visual alerts (Red Master Warning + Message).

Trigger Conditions

The system activates if any of the following parameters are not in the approved takeoff position:

1. Flaps / Slats: Not within the approved takeoff range (or not set).
2. Longitudinal Trim (Stabilizer): Not in the green band (Takeoff Range).
3. Spoilers / Speed Brakes: Deployed or not in the safe takeoff position.
4. Parking Brake: Set or not released.
5. Flight Controls: Control locks engaged (if applicable).
6. Doors: Essential external doors not closed and locked (on some types).

Operational Use

• Test Function: Modern aircraft (like the Airbus A320) include a T.O CONFIG pushbutton. Pressing this simulates the application of takeoff power to check if the current configuration is valid. If it is, a specific message (e.g., "TO CONFIG NORMAL") is displayed.
• Inhibition: The warning is typically inhibited after a certain speed ($V_1$ or $V_R$) to effectively prioritize alerts and avoid distraction during the critical rotation phase.