What Is a Flap Check and Why Is It So Important?

A flap check is a verification pilots perform to ensure an aircraft’s flaps are in the correct position for a given phase of flight. This procedure confirms that these wing components are functioning as expected. Pilots execute this check before takeoff and landing, phases where the aircraft’s speed and altitude are lowest and aerodynamic control is most demanding. This methodical action is ingrained in pilot training and contributes to the safe handling of the airplane.

What Are Aircraft Flaps?

Aircraft flaps are hinged surfaces on the trailing edge of the main wings. Their primary purpose is to alter the wing’s shape to increase both lift and drag when deployed. This modification allows the aircraft to generate sufficient lift to maintain flight at slower speeds. This capability is important during takeoff and landing, where operating at lower velocities is necessary.

By extending the flaps, a pilot increases the curvature, or camber, of the wing. This change in shape forces air to travel a longer path over the top surface, which lowers the air pressure above the wing and increases the lift it produces. While flaps come in several designs, such as plain or slotted, the goal is to enable slow, controlled flight and steeper descent angles without a significant increase in speed.

Why Flap Checks Are Crucial

Correct flap settings are directly tied to an aircraft’s performance and safety. A flap check ensures these settings are accurately applied for takeoff and landing. During takeoff, a specific flap setting is calculated based on factors like aircraft weight and runway length. Using the wrong setting could prevent the aircraft from generating the necessary lift to become airborne within the available runway.

The check is also important for landing. Extending the flaps allows the pilot to fly a steeper approach to the runway without building up excessive speed, providing a better view of the landing area. It also enables a lower touchdown speed, which shortens the landing roll once on the ground. Verifying that both flaps are set symmetrically is part of the check to prevent control issues.

When and How Flap Checks Are Done

Flap checks are integrated into standardized checklists that pilots follow. The process begins during the pre-flight walkaround, where the pilot visually inspects the flaps and their mechanisms for any signs of damage. Before takeoff, as part of cockpit preparations, pilots set the flaps to the calculated position for departure. This action is followed by a verbal confirmation between the flight crew.

During flight, particularly when preparing to land, flap deployment is a multi-stage process. As the aircraft slows to a safe flap-operating speed, pilots extend the flaps in increments. For example, on approach, a pilot might first select a small flap extension, then add more as the aircraft gets closer to the runway. Each selection is accompanied by monitoring the flap position indicator in the cockpit and cross-verifying the setting with the other pilot.

Risks of Improper Flap Management

Failure to perform flap checks or incorrect management of flap settings can lead to operational risks. Setting the flaps incorrectly for takeoff could result in a failure to achieve liftoff, leading to a runway overrun. If flaps are deployed at too high a speed, it can cause structural damage to the flap system or the wing itself. This is why there are speed limitations for each stage of flap extension.

An undetected issue, such as an asymmetric flap deployment, can have severe consequences. This condition, where one flap extends or retracts while the other does not, introduces a strong, uncommanded roll that can be challenging to counteract at low altitudes. In a landing scenario, incorrect flap settings can also lead to a high approach speed, resulting in a longer landing distance than the runway can accommodate.