What character must the first letter in an aircraft designation be?

The first character in an aircraft designation must be a letter, as per the standards set by the International Civil Aviation Organization (ICAO) and the Federal Aviation Administration (FAA). This is a fundamental aspect of aircraft registration systems.

The aircraft designation typically starts with a letter that indicates the country of registration, followed by a combination of numbers and additional letters that are specific to the individual aircraft. For instance, in the United States, the designation usually begins with an 'N' followed by a series of numbers and letters, where the 'N' signifies the aircraft is registered in the U.S.

Understanding this rule is crucial for recognizing aircraft types and for communications in air traffic control, as it helps to avoid confusion over identification.