Can Airliners Glide?

by | Mar 15, 2017

Commercial airliners are designed to fly after losing a single engine.  The airplane manufacturers are required to show the performance of their airplanes after losing an engine and they have to be able to fly, fully loaded, for three hours on only one engine (for twin engine aircraft). In order to fly over open water and in remote areas without airports close by the plane must maintain a history having 1 hour or less or engine failure per 100,000 hours of flying time.  So, while having an engine fail is not unprecedented it is not a common occurrence.

What happens when a plane loses power to all its engines? Believe it or not, commercial airplanes have the ability to glide . A fully loaded 747 has a glide ratio of 15:1 meaning that it travels 15 feet horizontal for every foot of vertical drop.  That means at 35,000 feet it could travel about 100 miles. The new 787 Dreamliner is around 20:1.  As a comparison, a Cessna 172 (little single engine plane) has a glide ratio of 9:1 – not as good as airliners.  The glide ratio is mainly dependent on aerodynamics, not size.

Example – on August 24, 2001 Air Transat Flight 236 ran out of fuel over the Atlantic Ocean with 306 people on board.  The plane was an Airbus A330 and its engines flamed out due to a fuel leakage issue.  When the engines flamed out, important systems became unavailable – the aircraft lost its main hydraulic power which operates the flaps, brakes, and spoilers. Additionally, an aircraft without operating engines cannot use its thrust reversers to slow the plane after touchdown. The pilots of the Airbus A330 were able to glide the aircraft to a landing at Lajes Air Base, Terceira Island in the Azores. They were able to glide for 20 minutes and 115 miles to the airport.  The reported landing speed was about 200 knots indicated airspeed, higher than the normal speed of 130 to 145. There were no fatalities, but there were minor injuries.

Another example:  Air Canada Flight 143.   On July 22, 1983 at 41,000 feet flight 143, a Boeing 767, ran out of fuel.  Without power the plane lost almost all of its navigation and instrument systems.  The pilot used to be in the Royal Canadian Air Force and knew of an airbase not too far away.  Little did he know that the runways were being used for a “family day” and were filled with classic cars.  The 767 was able to glide to the airbase and land.  The front landing gear did not lock so it skidded along its belly which actually helped it stop.  The plane came in so low over a golf course that one of the passengers remarked: “Christ. I can almost see what clubs they’re using”.  The aircraft came to rest only a few hundred feet from the people gathered at the end of the runway for Family Day. None of the 61 passengers suffered more than minor injuries.  It was calculated that during the glide the 767 had a glide ratio of 12:1 – meaning that it moved 12 feet forward horizontally for every 1 foot of vertical drop. So, at 40,000 feet this would translate into being able to glide for approximately 90 miles.  Coincidentally, the mechanics sent from Winnipeg Airport in a van ran out of fuel on their way to the airbase and found themselves stranded. Another van was sent to pick them up.

A famous example is the US Airways flight that Captain Sullenberger landed on the Hudson after losing both engines due to geese striking the engine. There are other examples.

A few years ago I sat next to a Southwest pilot on a flight.  I asked him what the chances were that he’d be able to glide and land a 737 from 35,000 feet that had lost both engines.  He said he thought 95% chance that he’d be able to safely land  – that they train in simulators for such events.


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