Aeronautical navigation data is the information about airports, air routes and landing procedures that every aircraft and flight bag must carry, updated worldwide on a fixed 28-day cycle. It is the data that makes a chart on a pilot's tablet correct. The cycle is also called AIRAC, which stands for Aeronautical Information Regulation and Control.
Pilots need the data to know where the runways are, which routes they may use and how to approach an airport in bad weather. These details change: a runway is renamed, a route is added, a landing procedure is revised. If every country changed its data on a different day, an aircraft might carry old data. So the whole world follows the same 28-day cycle. Every 28 days, a new set of data takes effect on a known date. That makes 13 cycles in most years and 14 in a few. In India, the Airports Authority of India is the body that publishes the country's changes. Data providers collect the changes from each country's authority, prepare the new set and publish it before the date.
Say a pilot in Lucknow is about to fly to Kolkata. Before the flight, the pilot checks the cycle date shown in the app. If the data has expired, the pilot must normally update it first. The rules allow a flight with the old set only in rare cases, with extra checks against current charts. The same check applies to the aircraft's own navigation computers, which engineers load with the new data. If the aircraft and the flight bag showed different cycles, the pilot could be looking at one landing procedure on the chart while the aircraft's computer follows another.
The data goes to two places: the pilot's electronic flight bag and the aircraft's own avionics. Both must show the same cycle. It is one of the safety records of aircraft maintenance and flight operations, and it follows the discipline of safety certification. Position on the chart is drawn using digital maps and location data.