The Complex Pushback

Every commercial flight begins with the highly choreographed pushback from the terminal gate.

When you think about it, the commercial aircraft pushback is a necessary yet surprising aspect of flight. An aircraft capable of flying anywhere between 500 and 600 hundred miles per hour requires assistance to move backward from a gate at an almost immeasurably slow speed. Nearly every flight starts the same way. The captain releases the parking brake and the aircraft is pushed back from its parking stand aided by a small, but powerful tug which moves the plane away from the terminal. A choreography of triggers and responses are used during every pushback. Let's see how they play out.

Proper weight and balance is critical for aircraft safety, performance, and structural integrity. 

Before anyone can start thinking about the pushback, the boarding door needs to be closed and the jetbridge disengaged from the airplane. In order to close the door, flight attendants are required to conduct a passenger count that matches the number of tickets scanned by the gate agent. Additionally, passengers need to be seated in the zone of the aircraft in which they were ticketed for weight and balance purposes. This is necessary because aircraft are balanced like a giant seesaw, where the wings act as the pivot point. Seating passengers in specific zones ensures the airplane’s Center of Gravity remains within the strictly defined safe “envelope” required for stability and controllability. 

Flight attendants are tasked with ensuring counts are correct and passengers are in assigned seats.

A miscount or discrepancy requires resolution before the boarding door can be closed. This is why flight attendants often request passengers take their assigned seats as quickly as possible. When gate agents or flight attendants request a certain passenger to ring their call button, it's usually not because there's uncertainty if they're on the plane. Rather, that passenger has taken a seat other than the one in which they were ticketed, resulting in a possible weight and balance discrepancy. I’ve been on multiple aircraft over the years when the cabin crew needed to shift passenger seating to ensure proper balance during the flight.

Red beacon lights are located on the very top and bottom of the fuselage, generally near the middle.

Pilots typically activate the plane's red beacon lights before initiating pushback, immediately prior to or during the engine start sequence, to signal that the aircraft is about to move and that engines are active. They serve as a warning to ground crew that the aircraft is live, ensuring safety before, during and after pushback. (The beacons remain active until engines are shut down at the arrival gate, warning ground staff to stay clear.) Activation of the beacons, along with the removal of the jet bridge, is a cue to  ground staff that pilots are ready to contact them for pushback. Ground crews normally then connect a headset jack near the plane's nosewheel. Most commercial aircraft have an indicator light in this area that shows when the pilots have disengaged their ability to steer the plane and have released the parking brake. Both of these are requisite items for a ground crew to push a plane. If the crew tried pushing a plane back without the steering disengaged or the parking brake set, there would almost certainly be damage to the nosewheel assembly. 

Communication between tug drivers and pilots is critical to situational awareness in congested areas.

With the headset having been connected, the tug driver now has direct communication between him or herself and the pilots. Large airports have ramp controllers that issue push and start clearances to pilots. After the captain and tug driver have confirmed mutual readiness, the first officer normally calls the ramp tower for clearance. Once approved, that information is then relayed by the pilots to the tug driver. In the event that headset communications aren't available, there are a series of standard hand signals that pilots and ground crew use to rudimentarily communicate this information. Engines are started during most (but not all) pushbacks. Some airports and airlines have policies that forbid engine starts during pushback for safety reasons. If the engines are allowed to be started during the push, the go-ahead is always given by ground staff. Pilots are trained to never start an engine before being told it's safe to do so by the tug driver. During most pushbacks, wing walkers with marshaling batons are present at both wingtips to ensure clearance. One arm raised and one arm parallel to the ground means it's clear to push, while crossed batons in the shape of an "x" are an indication to stop the push immediately.

Pilots are in constant communication with both ground control, and ground crew to ensure safety.

Once completed, the tug driver will next request the captain to set the parking brake. The captain does so and then clears the ground crew to disconnect and remove the tug. Policies differ by airline, but most ground crews stand in the pilot's field of vision while disconnecting the ground equipment. Before walking away, the person who disconnected the headset and towbar (if used) holds a pin or strap above their head for the pilots to view. A pin is used to override steering on some aircraft, while a strap is used to hold other planes in position on lift-type tugs. Regardless of which is employed, this indicates that every external item used to push the aircraft has been removed and that it’s safe for the pilots to taxi. Pilots will next move the flaps and slats into the takeoff position and also check the flight controls.

The MD-80, the backbone of the American fleet, could power back from the gate without pushback.

Some planes were capable of a power back maneuver. All but lost to a previous era of flying, it was once common to see McDonnell Douglas MD-80 variants and DC-9s powering back without needing a pushback tug. The thrust reversers, known commonly as "buckets" or "clamshells," would deploy as shields against the backward thrust produced by the engines. Thanks to their design, as well as their higher mounting points on the aft fuselage of the aircraft, MD-80s and DC-9s could reverse off the gate if necessary. American Airlines operated a massive fleet of MD-80 aircraft (often called “Super 80s” or “Mad Dogs”), totaling over 360 aircraft at their peak in the early 2000s. American was the first major US carrier to order them in 1982 and the planes became the backbone of their network for 37 years before being retired in 2019. However, power backs were loud and created high amounts of smoke. They also ran the risk of Foreign Object Damage from debris besides being fuel-inefficient, all of which lead to their general abandonment in favor of tugs.

Aircraft pushback is often described as a highly choreographed, high-stakes performance similar to an orchestra, requiring precise synchronization between ground crews, pilots, and controllers to safely move a plane away from the gate.

Until next time…safe travels.