how does autopilot work on a plane

We’ve all wondered what the captain means when they say that the plane is in auto-pilot mode. Does it mean that the plane has a brain of its own and the pilot is free to take a nap? Well, not exactly.

It’s a flight control system that allows the pilot to fly the airplane without having to continuously control the aircraft physically. It works on the negative feedback loop model. This means that the system will react to feedback in a way that maintains equilibrium. There’s a sensor that absorbs data and the system will use that data to function in a pre-set way i.e. lateral and vertical movement. An Automatic Flight Control System or Autopilot as we know it is made up of three main parts. A flight monitoring computer, high speed processors and a series of sensors placed on different parts of the plane. These sensors collect data from the entire plane and send them to the processors. The processors will then pass on this information to the computers.

There are mainly three levels of complexity. There are single, two and three axis autopilots based on the number of parts they control. Single axis autopilot controls the ailerons that helps the wings of the plane remain perpendicular to the ground and is also called the wing leveller. Two axis autopilot does everything that the single axis mode does along with controlling that elevators. Three axis does all this and controls the rudder. The computer tells the servo mechanism what to do. The servos are the instruments that move all the parts.


Now, the success of the autopilot depends on the knowledge of the captain. According to Former Major Airline Captain, Greg Zahornacky, autopilots are dumb and dutiful which means that they will do what is told even if the input is illogical, and the computer will attempt to fly whatever is put in. The first step the captain follows is inputting a flight plan. The route inserted by the captain is the flight plan. If this is wrong, the plane could fly around in circles or in whatever wrong direction is inserted. Step two is only to turn on the autopilot. The system navigates the flight plan and takes over.

Autopilots are ultimately systems and can fail which is why a human pilot will always be there. A user error or a sensor error is possible. The solution is simple. The captain will disengage the autopilot and conduct step one again or will fly the plane manually. The autopilot isn’t capable of making decisions and taking full control of the aircraft. We don’t have to worry because we still have pilots who take annual exams called a check right to keep their licences updated and their skills in place.