Final answer:
The equipment required when flying over water within 50nm of an emergency landing site is life jackets. An ELT is also important for emergency location signaling, but not specific to the question's scope.
Step-by-step explanation:
When flying over water, especially within 50 nautical miles (nm) of a potential emergency landing site, it is essential to have the right safety equipment on board. The best answer to what equipment should be on board is A) Life jackets. These are crucial for passenger survival in the event of a water landing. While an ELT (Emergency Locator Transmitter) is also very important, it serves a different purpose of signaling your location to rescue personnel in the event of an emergency. The DME (Distance Measuring Equipment) and TCAS (Traffic Collision Avoidance System) are both valuable pieces of navigation and collision-avoidance equipment, but they are not specifically required for over-water flights within 50nm of shore as per the question's guidance. It is always important to consult current aviation regulations based on the aviation authority in your region for the most accurate and up-to-date requirements.