The Role of Automatic Flare in Autoland Systems: How Do Planes Land Themselves?

In the realm of aviation, modern technology has revolutionized the landing process of aircraft through autoland systems. These sophisticated systems enable the aircraft to execute a landing with minimal or no pilot intervention. Today, we delve into the nuances of the automatic flare maneuver during an autoland, exploring how planes practically “flare” themselves without direct human input.

Descent Phase

The autoland process begins with the aircraft descending on a predefined glide slope, typically guided by the Instrument Landing System (ILS). This pre-programmed glide path ensures that the plane approaches the runway with precision, enhancing safety and reducing the reliance on manual adjustments.

Automatic Flare

As the aircraft nears the runway, the autoland system initiates a critical maneuver known as the 'flare.' This involves a slight upward movement of the aircraft's nose just before touchdown. The goal is to reduce the descent rate and create a stable, gentle landing, which is crucial for maintenance of the aircraft's stability and comfort for passengers.

Touchdown

The autoland system is responsible for managing the main gear touchdown, ensuring that the plane aligns precisely with the runway. This precision is vital, as it minimizes the risk of off-centre landings and enhances overall flight safety.

Rollout

Following touchdown, the aircraft continues to roll out along the runway. During this phase, the autoland system may engage various auxiliary systems like brakes and thrust reversers. The rollout phase is critical for further deceleration and stabilization, contributing to a safe and smooth landing sequence.

737 Autopilot Engagement and Flare Mechanics

For Boeing 737 aircraft, the second autopilot is engaged under specific criteria. This occurs when the aircraft is on course to intercept the final approach course, with the intercept taking place at or above 1500 feet Above Ground Level (AGL). The localizer final approach course must be inbound, and the glide slope should indicate normal readings without any flags.

When the altitude preselect is at 100 feet below field elevation as the aircraft intercepts the glide slope, both autopilots track the localizer and descend on the glide slope. A relay opens, providing separate engine generator power to each autopilot. Around 300-400 feet above ground level (AGL), both autopilots will roll in approximately 3 turns of the trim wheel, requiring the application of forward stick pressure from the autopilots.

Continuing the descent at 27 feet AGL, the autothrottle gradually retards the thrust. The plane maintains a nose-high attitude due to the nose-up trim, ensuring a smooth touchdown on the main gear.

Upon wheel spin-up, the spoilers deploy to eliminate lift, and the autobrake is applied according to the schedule set on the switch. The pilots, meanwhile, manually pull the thrust levers into reverse and steer the aircraft with the rudder as the plane decelerates and stabilizes.

Conclusion

The automatic flare plays a pivotal role in the autoland process, allowing planes to land smoothly and safely without manual pilot intervention. Modern aviation technology continues to evolve, making air travel safer and more efficient.