What must a pilot do if a passenger seat has a defective shoulder harness before flight?

If a passenger seat has a defective shoulder harness before flight, the pilot must not allow the flight to proceed. This is essential for safety, as the shoulder harness is a critical component of the passenger restraint system. Its primary role is to help secure passengers in their seats during the flight, particularly in the event of turbulence or an accident. If this safety device is defective, it compromises the protection it provides, increasing the risk of injury to the passenger.

By not allowing the flight to proceed, the pilot ensures that all passengers are properly secured, adhering to safety regulations and best practices in aviation. This decision reflects the pilot's responsibility to prioritize safety for everyone onboard and to ensure that all safety equipment is functional and effective before takeoff.