What equipment must be present for an aircraft flying under IMC?

For an aircraft flying under Instrument Meteorological Conditions (IMC), it is essential to have specific equipment to ensure safety and operational efficiency. A vacuum system and an alternate static source are crucial components.

The vacuum system is necessary for powering instruments such as the attitude indicator and the heading indicator, which are vital for situational awareness when visibility is limited. These instruments rely on a vacuum source to provide accurate readings during flight, especially when flying solely by reference to instruments.

An alternate static source is also important, as it provides a backup air pressure source in the event that the primary static system becomes inoperative due to blockage or malfunction. This redundancy ensures that critical instruments remain operational, allowing pilots to maintain control and navigation capabilities even in adverse conditions.

While the other choices may enhance an aircraft's capability or safety features, they are not mandated for flying under IMC conditions as the vacuum system and alternate static source are. Therefore, having a vacuum system and an alternate static source is crucial for compliance with safety regulations and to ensure the pilot can safely navigate and operate the aircraft in IMC.