What Happens When an Aircraft's Engine Stops? Gliding, Explained

Why it glides instead of falling

A wing makes lift from the air flowing over it, not from the engine. The engine's job is to keep the speed up. When it stops, the pilot lowers the nose and lets gravity do that job: the aircraft gives up height, steadily, in exchange for speed. The FAA's flying handbook calls the result the glide ratio, the distance an aircraft travels for the height it loses. In its example, an aircraft that goes 10,000 feet forward while descending 1,000 feet has a glide ratio of 10 to 1.

Best-glide speed: the one number that matters

Every aircraft has one speed at which it glides furthest in still air: the best-glide speed, where the ratio of lift to drag is highest. The FAA handbook says that faster or slower than this, drag increases and the glide ratio gets worse. So raising the nose to stretch the glide does the opposite: the aircraft slows, comes down more steeply and moves towards a stall. Wind matters too. The handbook notes that a tailwind lengthens the glide over the ground and a headwind shortens it.

Just after take-off: land straight ahead

The hardest case is an engine failure low down, just after take-off. The FAA handbook says the pilot should lower the nose and establish the glide, and that landing straight ahead, or with a slight turn, is usually the option with the lowest risk. Turning back to the runway is known as the impossible turn. In the FAA's worked example the engine fails at 300 feet. After 4 seconds to react and a standard-rate turn of 225 degrees that takes 75 seconds, an aircraft descending at about 1,000 feet per minute has lost 1,316 feet, which would put it 1,016 feet below the runway.

How the aircraft touches down matters more than where. The handbook says the touchdown should be made at the lowest possible controllable airspeed, because doubling the groundspeed quadruples the destructive energy, and that a well-executed landing in poor terrain can be less hazardous than an uncontrolled touchdown on an established field.

What about an airliner?

Airliners have more than one engine. US airline rules say that whenever an engine fails, or is shut down to prevent possible damage, the pilot in command must land at the nearest suitable airport, in point of time, at which a safe landing can be made; aircraft with three or more engines have some leeway.

For passengers this usually looks like a diversion: an unplanned landing, a wait and another aircraft. Stay seated with your seat belt fastened, listen for announcements and follow the crew's instructions.