Boeing 787's Emergency-Power System Likely Active Before Air India Crash

Investigators believe Air India Flight 171 had an emergency-power generator operating when it crashed last week, raising questions about whether the plane's engines functioned properly during takeoff. WSJ: The preliminary finding [non-paywalled source], according to people familiar with the probe, gives investigators a new line of inquiry as they study a crash that killed all but one of the plane's passengers. In all, at least 270 people died following the crash, including some on the ground in the western Indian city of Ahmedabad.

The emergency system is known as a ram air turbine. It is a small propeller that drops from the bottom of the 787 Dreamliner's fuselage to serve as a backup generator. Engines normally produce electricity for an aircraft and help run its flight-control systems. The power generated by the RAT can enable crucial aircraft components to function. The system can deploy automatically in flight if both engines have failed or if all three hydraulic system pressures are low, according to an airline's Boeing 787 manual reviewed by The Wall Street Journal.

It can also deploy if cockpit instruments lose power or problems emerge with the aircraft's electric motor pumps. Pilots can manually deploy the RAT if needed. The most common occurrence is when a pilot thinks that both engines failed, according to Anthony Brickhouse, a U.S.-based aerospace safety consultant. Engine failures can result from a variety of causes, including bird strikes or problems with fuel.

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