Describe a 'beacon' in the context of aircrew survival gear.

A 'beacon' in the context of aircrew survival gear is a signaling device specifically designed to indicate a person's location for rescue purposes. In survival situations, beacons play a critical role as they allow the stranded or lost individuals to communicate their position to potential rescuers, significantly increasing the chances of recovery. These devices can emit signals such as visual lights or radio frequencies, which are detectable by search and rescue teams, enabling them to locate the user quickly.

The other options do not accurately describe the function of a beacon. A radar system for navigation, for example, is primarily used for determining position and direction during flights, rather than aiding in individual rescue efforts. An onboard communication tool facilitates communication within the aircraft rather than signaling for external rescue, and a device for tracking weather changes serves an entirely different purpose related to situational awareness rather than signaling distress. Therefore, the primary function of a beacon as a distress signaling device is what makes it the correct answer in this context.