Ultimately, it boils down to logistics and safety. Jet bridges are always designed to match up with the left side of aircraft, and by loading passengers from the left side of planes, the right side is available for other potentially dangerous activities, from cargo loading to refueling.

Entering an aircraft from the left side (the Port side) is a tradition deeply rooted in maritime history that was carried over into early aviation. In the days of sailing ships, the right side was the "Steer-board" (starboard) where the steering oar was located; to avoid damaging this critical rudder, ships always docked with their left side against the pier, which became known as the "Port" side. When commercial aviation began to standardize in the 20th century, engineers and pilots adopted this nautical convention. By 2026, this has become a rigid structural standard: airports are designed with jet bridges on the left, and aircraft are built with the main passenger doors on the left and service doors (for catering and baggage) on the right. This physical separation of passengers and ground services is vital for safety and efficiency, as it prevents travelers from walking into the path of refueling trucks, baggage loaders, and catering lifts that operate simultaneously on the starboard side to ensure a quick turnaround.