1983

Gimli Glider

Imagine that you are the pilot flying a state-of-the-art Boeing 767. You are cruising at 41,000 feet (12,500 meters) over Canada. It should be a routine flight, but suddenly you start hearing warning chimes and there are lights flashing on the instrument panel. Multiple parts of the airplane have started to complain all at once about low fuel pressure. The plane has run out of fuel midflight.

Both jet engines shut down. The 767 is now a glider.

The thing to understand is that a 767 is a hydraulically powered plane. The steering yoke and pedals drive hydraulic cylinders that move the control surfaces like the rudder and the ailerons. Without engines to pump the hydraulic fluid, there is a big problem.

This incident, which is known as the Gimli Glider because of the airport where the plane ended up landing in 1983, shows one of the true hallmarks of good engineering. Engineers not only solve problems; they can anticipate them and design for fail-safe redundancy.

In the case of this 767, there was already redundancy. Both engines have the ability to pump hydraulic fluid. So if one engine fails, the other one can handle the load. But both engines are dead. Now what? Another level of redundancy: the electric backup hydraulic pump in case both engine pumps fail. However, it depends on an electrical generator working on one of the engines. With both engines dead there is no electricity.

A small battery backup system provides minimal electrical power in a situation like this. It kicks in to power a few instruments and the radio. But it has nowhere near the power to run a hydraulic pump. But these batteries can open a small door on the underside of the fuselage. And out pops something amazing—the ram air turbine (RAT). Engineers designed it to handle exactly this situation—a dual engine failure. It uses wind passing by the fuselage to spin a turbine that pressurizes the hydraulic system. The plane landed without any casualties because of the RAT.

It is a great example of engineers anticipating unexpected problems in order to save lives.

SEE ALSO The Wright Brothers’ Airplane (1903), Turbojet Engine (1937), Boeing 747 Jumbo Jet (1968).

The Gimli Glider is shown here.