Final answer:
The second character in the ICAO code is used to denote the type of flight.
Step-by-step explanation:
The second character in the ICAO code is used to denote the type of flight. Let's match the flight type letters with the categories:
- N - General aviation
- S - Military
- M - Other than the preceding categories
- G - Scheduled air service
- X - Non-scheduled air transport operation
So, for example, if the appropriate ATS authority requires the flight type letter to be 'G', it means the flight is a scheduled air service.