Awesome demonstration of reverse thrust on landing

An EVA Air Boeing 747-400 lands at Singapore Changi after heavy showers. Standing water on the runway is thrown up in a wall of spray the moment the reversers deploy, and the wings visibly unload as the aircraft settles.

What you are watching

The spray. Thrust reversers do not run the engines backwards. On the 747’s high-bypass turbofans, blocker doors and cascade vanes redirect the bypass air — the cold air that goes around the core — forward and outward at an angle. That is what picks up the surface water and throws it ahead of and around the aircraft.

Because it is bypass air rather than exhaust, most of a 747’s reverse thrust comes from the fan, not the hot core. It is also why reverse is far more effective at high speed than low: there is more air moving through the fan.

The wing flex. Watch the wings as the weight transfers onto the gear. In flight a 747’s wings carry the entire aircraft and bow upward; on touchdown that load moves to the landing gear and the wings drop. The movement looks alarming and is entirely normal — a 747 wing is tested to bend far past anything it will meet in service.

Why reversers matter less than you would think

Reverse thrust is not credited in the certified landing distance for most operations. Regulators require an aircraft to be able to stop on wheel brakes and spoilers alone, so the reversers are margin rather than the primary means of stopping.

What they genuinely buy is brake wear and heat. Brakes convert energy to heat, and a 747 arriving heavy generates a great deal of it. Using reverse takes a share of that energy out of the brakes, which matters for turnaround times — hot brakes need to cool before the next departure.

On a wet runway they buy something else again: reverse thrust works the same whether the surface is wet or dry, while braking does not.

Related

• Rejected takeoff — where stopping really is critical
• The 747-8’s new wing
• The 747-400