Final answer:
A crash axe is required under Federal Aviation Regulations Part 91, Subpart F for aircraft designed with seating configurations for more than 19 passengers, ensuring added safety measures for emergency situations.
Step-by-step explanation:
The question specified pertains to the equipment requirements outlined in Federal Aviation Regulations (FAR) under Part 91, Subpart F, which pertains to large and turbine-powered airplanes. According to these regulations, an aircraft is required to have a crash axe on board if it is designed to have a seating configuration, excluding pilot seats, accommodating more than 19 passengers. This requirement is aimed at ensuring the safety of passengers and crew by providing a tool that can be used for emergency egress or to fight fires should the need arise during flight or after an emergency landing.