American Airlines jets, which weigh up to 400 tons, cruise at speeds in excess of 600 miles per hour. So, as you might imagine, the process of bringing such a huge mass to a landing speed of about 150 miles per hour, then slowing it down very quickly to a safe taxi speed, is as complex as it is important.
The landing process begins before the aircraft leaves cruising altitude, when pilots check the weather via either text message or radio. Most of the time, this initial check also lets the pilots know which runway to plan on for landing, whether any delays are expected, and if extra preparations should be made, such as the use of the aircraft’s anti-ice equipment.
As the aircraft approaches its destination and begins its landing descent, the pilots do several things to reduce speed. After throttling back the engines, they deploy devices known as spoilers, which are sometimes referred to as air- or speed-brakes. They are small panels that rise at a near 90-degree angle from the upper surface of the wing as the aircraft prepares for landing. They function by further breaking up — or spoiling — the flow of air over the wings. As the aircraft’s speed decreases below 250 miles per hour, the pilots extend the slats — devices on the front edge of most aircraft wings — and the flaps that are on the rear edge of all wings. These mechanisms extend the wing’s surface, thus improving aerodynamic efficiency at slower speeds, while simultaneously helping to maintain the wing’s lift.
While the slats come out from the wing at an angle, the flaps are initially near horizontal and then lowered in incremental stages. When fully deployed for landing, they are at a 30- to 40-degree angle from the wing’s surface, depending on the type of aircraft.
Even our largest aircraft types have an average landing speed of 150 miles per hour. At touchdown, the automatic spoilers deploy, helping to further reduce the aircraft’s speed. At the same time, two other systems come into play.
One is the reversers on each engine, which redirect thrust to slow the airplane’s forward motion. During flight, air is drawn into the front of the engine, where it is compressed and thrust out the back, propelling the aircraft forward. Reversing the airflow after landing slows the aircraft quite quickly. The reversers block the air’s exit to the rear and force it to flow sideways and forward.
The last system used to stop the airplane is, of course, the brakes. An airplane’s brakes obviously have a bigger job to do than those of your car, and thus are heavier and more complex. Airplane brakes consist of multiple disks that are squeezed together to stop the wheels from turning. The disks and brake pads are made either from steel, like those in your car, or from a carbon material that weighs less and can absorb more energy. It’s the type of brake used on the space shuttle and some Indy-style race cars. Because airplane brakes are used principally during landings and must absorb enormous amounts of energy, their life is measured in landings rather than miles. Steel brakes are good for between 1,000 and 2,000 landings, while carbon brakes last for up to 2,500 landings, depending on the aircraft.
Now that you know all about slowing down and stopping, I hope you will sit back and enjoy your flight with full confidence that it will end in a smooth landing and carefully controlled stop, followed by what we hope will be an on-time — or earlier — arrival at your gate. Thank you for flying with us today.
GERARD J. ARPEY
President & CEO