Avionics are the electronics in an aircraft that handle navigation, communication and flight control. The word joins "aviation" and "electronics". The companies that make them are system suppliers. They often make cabins, landing gear and large parts of the airframe as well.
Avionics have three main jobs. Navigation systems work out where the aircraft is and where it must go. Communication systems let the pilots speak by radio with air-traffic controllers on the ground. Flight control systems move the control surfaces of the wings and tail, either on the pilot's command or automatically, as in an autopilot.
Imagine an aircraft descending towards Bhubaneswar. The flight computer holds the route, the height and the speed that the pilots have entered. It uses the airport and landing-procedure data in aeronautical navigation data, which is updated every 28 days all over the world. It sends commands to the control surfaces, and the pilots check the screens in front of them.
A single computer failing must not endanger the aircraft. So several computers do the same calculation at the same time and compare their answers. If one computer gives a different answer from the others, the aircraft uses the answer that most computers agree on, and the pilots are told about the faulty one.
The software inside these computers runs on a real-time operating system, which answers within a fixed time every time. Before it flies, the code is checked by static analysis tools and goes through safety certification. A mistake can cost lives, so changes are slow and carefully recorded. The aircraft maker chooses the avionics when it designs the aircraft. An airline can later replace older avionics with newer ones, but only after the regulator approves the change.
Avionics connect to the rest of the aircraft. They send position and speed to the cabin screens of in-flight entertainment. Pilots read charts and checklists on a tablet, the electronic flight bag. And pilots train for failures on a flight simulator that copies the avionics. An eVTOL air taxi also needs avionics, for its flight control.