When must airborne thunderstorm radar be installed on an aircraft?

Airborne thunderstorm radar must be installed on an aircraft when thunderstorms may reasonably be expected on route because this is a critical safety measure that enables pilots to detect and avoid potentially hazardous weather conditions. Thunderstorms can produce severe turbulence, lightning, heavy precipitation, and other dangers that can adversely affect flight operations. The radar provides real-time information about the location, intensity, and movement of thunderstorms, allowing pilots to make informed decisions and alter flight paths as necessary to maintain safety.

Choosing to install the radar based on the reasonable expectation of thunderstorms also aligns with regulatory and operational safety practices, as it ensures that pilots are equipped to navigate within areas where adverse weather could pose a significant risk to the flight.

The other scenarios, while they may involve certain risks, do not specifically relate to the need for radar based on the likelihood of thunderstorms. For instance, flying at night or over mountainous terrain poses different challenges but does not inherently necessitate the presence of airborne thunderstorm radar. Operating above 10,000 feet introduces different flight dynamics but does not directly correlate to weather detection requirements related to thunderstorms either.