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Why Is There A Propellor on the Boeing 787 Dreamliner?


 Did you know that the 787 can deploy a propellor underneath its fuselage?  It’s called a RAT.  Not the furry animal, but a propellor that provides an auxiliary source of electrical power in the case of dual engine failure.

If you look closely at the video below, you’ll see that this video shows testing of the 787’s ram air turbine (RAT). It’s a small propellor installed on each side of the fuselage that can be used as an additional source of power in the event of a dual engine loss. It generates its power from the airstream by ram pressure.  The RAT is meant only as an emergency power source for the aircraft in the event that both engines fail.  It provides enough electrical power to power only one of the 3 electric hydraulic systems on the jet.  If you have to use it for real, you are having a really bad day.

The RAT is tested before delivery.  It’s also tested occasionally during revenue service.  Once the RAT is deployed, it can’t be retracted.  It has to be stowed by maintenance personnel after landing.

The Dreamliner is an amazing aircraft but it has had its fair share of problems, even lately.  We reported recently on Avgeekery.com, that the FAA is requiring some Dreamliner engines to be replaces as part of an emergency directive.

Icing issues on certain models of the General Electric engines on Dreamliners led to the Federal Aviation Agency to issue a directive to “urgently modify” those engines. The General Electric engine model GEnx-1B PIP2 is in question. Planes that are equipped with both engines of that model could potentially experience a catastrophic loss of both engines in flight.

Written by Wendell Barnhouse

Wendell Barnhouse is a veteran journalist with over 40 years of experience as a writer and an editor. For the last 30 years, he wrote about college sports but he has had an interest and curiosity about aviation since he was in grade school.