An electronic flight bag (EFB) is a pilot's tablet app that holds the charts, the flight plan and the weather that once filled a heavy bag of paper. Pilots used to carry that bag into every cockpit. Today they carry a tablet.
The app holds four main things. The first is the flight plan: the route, the fuel and the altitudes for the flight. The second is the charts, the maps of airports, air routes and landing procedures. The third is the weather along the route and at the destination. The fourth is the manuals the crew may need. The charts come from aeronautical navigation data, which is updated worldwide on a fixed 28-day cycle. Every flight bag must carry the current data.
Paper had two weaknesses. It was heavy, and it went out of date: every week or two, the airline had to replace pages in every pilot's bag by hand. An app is updated by a download, and the same data reaches all the pilots of the airline on the same day. It can also search, so a pilot finds a landing procedure in seconds instead of turning pages.
Imagine a pilot who flies from Mumbai to Delhi. Before departure, the pilot opens the app and loads the flight plan prepared by the airline's dispatchers. The app shows a storm over central India, and the pilot checks the alternative route on the chart. The pilot also reads the landing procedure for Delhi's runway in use. All of this is on one tablet instead of a bag weighing many kilograms.
The app is connected to other systems. It reads the aircraft's data from avionics, the electronic systems in the cockpit. It uses digital maps and location data to show the aircraft's position on the chart. The list of flights comes from the airline's passenger service system (PSS), while the airline's dispatchers prepare the flight plan itself. The airline also needs the regulator's approval before pilots use an EFB in place of paper. This is the pilot's side of aircraft maintenance and flight operations. An EFB is not a flight simulator; a simulator is for training on the ground.