Understanding what is Autopilot, Autopilot flying aircraft by its own through computer system. Flightpath stored In flight management and guidance computer.  Any modifications required by NOTAMS notices carried out pilot through MCDU.

Autopilot command executes by ELAC elevator and aileron computer and FAC flight augmentation computer with AUTO THRUST. So autopilot controls speed, attitude, altitude hold only and flight envelope protection. Auto thrust controls auto engine thrust in combination with autopilot. Now the pilot needs to monitor and communicate with towers at regular intervals.

Essentially, autopilot is a very smart and powerful computer that works similarly to a GPS. It can assist the pilot in flying the plane from departure to the touchdown at its destination.

Automatic flight control system (AFCS)

The autopilot is more accurately described as the automatic flight control system (AFCS). An AFCS is part of an aircraft’s avionics — the electronic systems, equipment, and devices used to control key systems of the plane and its flight.

In addition to flight control systems, avionics include electronics for communications, navigation, collision avoidance, and weather. The original use of an AFCS was to provide pilot relief during tedious stages of flight, such as high-altitude cruising.

Advanced autopilots can do much more, carrying out even highly precise maneuvers, such as landing an aircraft in conditions of zero visibility.

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Things about Take-off Every Pilot should Know

The first is the elevators, which are devices on the tail of a plane that control pitch (the swaying of an aircraft around a horizontal axis perpendicular to the direction of motion). The rudder is also located on the tail of a plane.

When the rudder is tilted to starboard (right), the aircraft yaws — twists on a vertical axis — in that direction. When the rudder is tilted to port (left), the craft yaws in the opposite direction. Finally, ailerons on the rear edge of each wing roll the plane from side to side.

Autopilots can control any or all of these surfaces. A single-axis autopilot manages just one set of controls, usually the ailerons. This simple type of autopilot is known as a “wing leveler” because, by controlling roll, it keeps the aircraft wings on an even keel.

A two-axis autopilot manages elevators and ailerons. Finally, a three-axis autopilot manages all three basic control systems: ailerons, elevators, and rudders.

Heading Hold

This will set the desired direction or heading that the pilot wants the plane to take. However, this doesn’t consider changes due to wind or the desired route; the pilot has to correct that himself.

Heading and Navigation

This setting will hold a direction as well as navigation. It’s similar to an automated car in that it follows the navigator’s input. The pilot continues to monitor as the plane flies.

Altitude Hold

In addition to everything above, this feature allows the pilot to set the desired altitude that the aircraft will fly. Some planes have a fancier altitude hold that lets the pilot set the desired climb or descend rate that will make the aircraft automatically climb or descend and then hold that altitude.

Instrument Approaches

This type of autopilot will fly pre-programmed instrument approaches. The only time the pilot must take over is to execute the landing.

 

Why do Airbus aircraft have two autopilot buttons?

They are controls for two separate autopilot systems that have the same functions and serve as a backup and crosscheck for each other.

The vast majority of aircraft used by airlines have multiple autopilot systems. These autopilots are essentially the same, they act as backups in case one of the systems fails. The number of autopilot systems depends on the complexity of the aircraft. A Dash 8 has two… A B-767 has three.

Normally one autopilot at a time handles the flying of the airplane. An exception to this rule typically occurs in approach mode, when two (in the Dash anyway) autopilot systems at a time are tied into the flight guidance computer to allow for immediate redundancy should one autopilot fail so near to the ground.

NOTE

Notwithstanding FAR 135.93(d), autopilot minimum-use altitudes do not apply to autopilot operations when an approved automatic landing system mode is being used for landing. Automatic landing systems must be authorized in an operations specification issued to the operator, however.

Kindly refer the available sources for more information, Sources:

Polic Handbooks From FAA

All about Autopilot System by Mightmech

The Lure of the Cheap Autopilot

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