According to ICAO procedures, when is IFR required?

The correct answer indicates that IFR (Instrument Flight Rules) is required for flight operations between sunset and sunrise, as well as during supersonic flight. This regulation is derived from ICAO (International Civil Aviation Organization) guidelines, which emphasize that certain conditions necessitate adherence to IFR for safety and operational efficiency.

During nighttime operations, visual references may be severely limited, prompting the need for pilots to rely on instruments for navigation and control of the aircraft. Additionally, supersonic flights may encounter specific airspace regulations that mandate IFR due to the complexities of managing such high-speed operations, ensuring that aircraft remain properly spaced and monitored.

In contrast, IFR is not specifically required for flights only under 10,000 feet, as numerous visual flight regulations (VFR) can apply at lower altitudes where visual reference is adequate. While it is true that flights exceeding FL180 often operate under IFR due to standard air traffic control procedures, this does not make IFR exclusively applicable to those elevations. Lastly, turbulence alone does not dictate a requirement for IFR, as pilots may choose to operate under visual flight rules if conditions permit.

Through these contexts, the necessity for IFR under specified conditions is clarified, emphasizing the importance of instrument-based navigation in ensuring safety across varied aviation scenarios