A tail number is an identification number painted on an aircraft, most often on the tail. Airliners operate both on flight numbers and tail numbers. The flight number is a virtual code, while tail numbers are physical codes. A person filling out the Ari Suvidha must provide a flight or tail number that must be a minimum of 4 to a maximum of 6 alphanumeric value. The flight/tail number cannot include space or any special characters.