What is UNLK on Boeing 737? (Unlock)

Unlock, abbreviated as UNLK, is a crucial feature on the Boeing 737 aircraft that allows pilots to manually extend and retract the leading edge slats and trailing edge flaps of the airplane’s wings. This function is extremely important as the position of these control surfaces directly affects the aircraft’s performance during takeoff and landing. Understanding how Unlock works and its significance in the operation of the Boeing 737 is vital for pilots, aviation enthusiasts, and anyone interested in learning about the technical aspects of aircraft.

Unlock: Enhancing Aerodynamic Performance

The Boeing 737 is equipped with slats and flaps that provide additional lift and maneuverability during different phases of flight. The leading edge slats, located on the front portion of the wings, help increase the wing’s surface area, allowing for a higher lift coefficient at lower speeds. On the other hand, the trailing edge flaps, positioned on the rear section of the wings, increase the curvature of the wing, thereby generating more lift and reducing the aircraft’s stall speed.

Unlock on the Boeing 737 allows pilots to manually control the extension and retraction of these slats and flaps, enabling them to optimize the aircraft’s performance based on various factors such as runway length, aircraft weight, and weather conditions. By adjusting the position of the slats and flaps, pilots can enhance lift, reduce takeoff and landing distances, and improve the aircraft’s overall aerodynamic characteristics.

During takeoff, for example, pilots typically select a configuration that maximizes lift while ensuring sufficient clearance from the runway surface. By extending the slats and flaps, the wing’s surface area is increased, generating more lift at lower speeds, which is crucial for a safe and efficient takeoff. On the other hand, during landing, pilots may choose a configuration that increases drag and lift to facilitate a controlled descent and a smooth touchdown. Unlock enables them to finely tune the slats and flaps to achieve the desired flight characteristics at each phase of flight.

Unlock Activation and Monitoring

To activate Unlock on the Boeing 737, pilots utilize the airplane’s Flight Management System (FMS) or the Flight Control Panel. By accessing the appropriate controls, pilots can either manually set the slats and flaps to the desired position or select predefined configurations based on specific flight conditions. The FMS provides the necessary guidance to ensure that the selected configuration aligns with the aircraft’s weight, speed, and other relevant parameters.

Once the Unlock function is engaged, pilots can monitor the position of the slats and flaps through the aircraft’s Primary Flight Display (PFD) and the Engine Indicating and Crew Alerting System (EICAS). These onboard systems provide real-time feedback on the status of the control surfaces, allowing pilots to confirm the accuracy of the selected configuration and make adjustments if necessary.

Additionally, an aural alert system is incorporated into the Boeing 737 to further enhance safety and prevent potential errors. This system, known as the Takeoff Configuration Warning (TCW), activates when the aircraft is not properly configured for takeoff, including the incorrect position of the slats and flaps. The TCW alerts the pilots, prompting them to verify the configuration and take corrective action before proceeding with takeoff.


Unlock on the Boeing 737 plays a vital role in the aircraft’s operational efficiency and safety. By enabling pilots to control the leading edge slats and trailing edge flaps, Unlock allows for precise adjustment of the aircraft’s aerodynamic characteristics during takeoff, landing, and other critical phases of flight. This feature enhances the Boeing 737’s performance, ensuring optimal lift, drag, and maneuverability based on the specific requirements of each flight. Pilots rely on Unlock and its associated monitoring systems to maintain the correct configuration of the control surfaces, guaranteeing a safe and smooth flying experience for passengers and crew alike.

For More: What is ACE on Boeing 737? (Actuator Control Electronics)