Final answer:
The requirement for a GPWS aboard an aircraft is typically based on the aircraft's MCTOW and authorized passenger configuration, often being required for planes with a MCTOW over 15,000 pounds or seating more than 9 passengers.
Step-by-step explanation:
The requirement for an aircraft to be equipped with a Ground Proximity Warning System (GPWS) is regulated and can vary depending on the jurisdiction. Typically, the requirement comes into effect based on the aircraft's Maximum Certificated Takeoff Weight (MCTOW) and the authorized passenger configuration. In the United States, for instance, the Federal Aviation Administration (FAA) requires that all turbine-powered airplanes with a MCTOW of more than 15,000 pounds or with an authorized seating configuration of more than 9 passengers must be equipped with an approved GPWS. This technology is crucial for enhancing safety by alerting pilots of potential terrain collisions, thus giving them time to take corrective action.