Have you ever noticed that whenever you board a commercial airplane, be that from a jet bridge or by ascending steps from the tarmac, you always board on the left-hand side of the plane? Do you know why?
While it’s a universally followed method, the reason isn’t commonly known. The answer lies in a combination of historical traditions and operational efficiency.
“It is one of the many aviation practices that goes back beyond aviation itself to the traditions of ships,” said Michael Oakley, managing editor of The Aviation Historian, a quarterly journal that explores the history of flying. “Much of aviation terminology had its origins in maritime lore (rudder, cockpit, cabin, bulkhead, knots, etc.), and similarly, the aeronautical ways of doing things owe a lot to sailing. Just as boats and ships have a port side—the side of the vessel conventionally adjacent to the dock when in port—aircraft are the same. Sensibly, people decided to continue to board on the port (or left) side.”
But in the the early days of commercial aviation, it didn’t “matter too much which side passengers boarded,” Oakley added. That was because passengers would always embark and disembark down steps on the tarmac.
“In the 1930s, the Boeing 247—the first modern airliner—had the passenger door open on the right, as was customary with United Airlines at the time,” said Bob van der Linden, a supervisory curator in the aeronautics department of the National Air and Space Museum in Washington, D.C. “When United purchased the excellent Douglas DC-3 in the mid-1940s, they ordered the aircraft with a right-hand door while most other DC-3 operators requested a left-hand door. Over time, as the industry grew and airports became increasingly busy, the left-hand door became the preferred arrangement so that airport operations could be streamlined and standardized.”
According to Matthew Burchette, senior curator at the Museum of Flight in Tukwila, Washington, standardization became more necessary in the 1950s, when star-shaped or “pier finger” terminals started to appear in the United States and Europe. These are airports like Chicago’s O’Hare, Amsterdam’s Schiphol, and London’s Gatwick, where passengers congregate in a central area and walk out into the fingers, or points of the star, to depart.
“Planes could now load passengers directly from the fingers into planes. During the 1960s, the design evolved to accommodate Jetways—the covered corridors that telescope out from the main terminal we are familiar with now,” Burchette said. “Since the pilot sits on the left, airports began to be built with gates on the left so the pilot could better judge distances as they taxied to the gate.”
Oakley echoed that explanation: “As soon as more complex airports were developed, with passengers using Jetways as a means of walking directly aboard from the terminal, ground operations were a lot easier if every aircraft did the same thing in the same direction.”
Boarding on the left also comes with an added bonus: “It allows the ground crew to go about their tasks without crowding the passengers or the gate equipment,” said Burchette. Having their own dedicated access area, where passengers won’t inadvertently get in their way or in the way of their heavy machinery, allows them to do their jobs more easily and faster, which in turn makes the travel day run smoother for all.