Final answer:
Airplanes avoid collisions by following FAA regulations that require maintaining specific lateral and vertical separations. Pilots contribute to this safety by accurately setting the aircraft's altimeter before takeoff, en route, and when approaching the landing aerodrome.
Step-by-step explanation:
The ability of multiple airplanes to fly simultaneously without collision is managed by rigorous regulations enforced by the Federal Aviation Administration (FAA). During flight, pilots are required to keep their aircraft at least five miles apart laterally from other planes at the same altitude and maintain a vertical separation of 2,000 feet (or 1,000 feet if flying below 29,000 feet altitude). These rules serve to create an invisible grid in the sky, defining safe zones for each aircraft, analogous to how electrons are restricted to certain energy levels in quantum mechanics.
To ensure safe navigation and adherence to these regulations, the pilot must accurately set the aircraft's altimeter. Before takeoff, the altimeter is set to the current setting of the departure aerodrome or to the aerodrome's elevation if the setting is unavailable. En route, the altimeter is adjusted to the nearest station along the path, or to the nearest station within 150 NM if stations are spaced further apart. Finally, when approaching the destination aerodrome, the altimeter is set to that location's current setting, if available.