You might think the world’s largest passenger plane, the A380, needs all the help it can get to come to a stop after landing. Based on that, why wouldn’t Airbus have reverse thrusters on all four of the A380’s engines? However, reverse thrusters are just one tool in the A380’s braking armory. When the A380 was designed, it was soon established that having reverse thrusters on all four A380 engines caused more issues than they solved.
What is reverse thrust?
A plane’s jet engines generate reverse thrust. Reverse thrust changes the direction air gets expelled from the engine. Primarily, reverse thrust is used to slow down the plane before it lands. Rather than pushing air out the back of the engines, the air gets pushed out the front of the engines when reverse thrust occurs. It’s a handy tool to help aircraft slow down, but not the only tool. Often you’ll see reverse thrust in action on wet runways just after landing as the turbulence from reverse thrust kicks up large amounts of water.
While reverse thrust does help slow an A380, and is even more useful if the runway is wet or slippery, brakes and spoilers typically play a bigger role in bringing the A380 to a stop. A380s also land at a relatively slow speed. They cross the landing threshold at 140 knots and sometimes touchdown going as slow as 130 knots. Despite being bigger and heavier than a Boeing 747-400, the Airbus A380 usually comes in at a more leisurely pace.
When the A380 was first designed, there was a debate about whether the plane would feature reverse thrust at all. A380s are designed to come to a complete stop using their brakes alone. Ultimately the decision was made to put reverse thrust on two engines to help minimize the risk of aquaplaning. But it was also decided that four reverse thrust on all four of the A380 engines was definitely overkill.
The A380 doesn’t need reverse thrust on all four engines
So the first reason why the A380 only has reverse thrust on two inside engines is because that’s all it needs. Further reverse thrust is surplus to requirements and simply adds to the plane’s overall weight and puts more stress on the wing structures. Adding reverse thrust to a single A380 engine adds half a tonne of weight to the plane. Given a fully loaded A380 weighs up to 1,265,000 pounds and is already expensive to operate, no-one is in a hurry to load the aircraft up with more weight.
There’s a final reason why there isn’t reverse thrust on an A380s outside engines. The A380s wingspan is 80 meters. Often the outside engines hang close to or over the edge of the runways. The more energy those engines put out, the greater the chance of debris damaging the plane’s wings and fuselage.
Aircraft generate a lot of turbulence when touching down. All that air rushing forward of the moving jet, especially around the runway’s perimeter, is potentially hazardous. It’s not such an issue when aircraft take off – they are leaving the turbulence in their wake.
It seems unlikely that such a big, heavy plane can come to a stop so easily, but there you have it. The A380 may often seem inelegant and lumbering, but it’s a superb piece of engineering. It could easily come in and land without any reverse thrust at all.