The noise was the sound of a cracked engine fan disk shooting out of the tail engine and freakishly hitting in the worst possible spot.

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But New England recently partnered with SessionM, a tech startup that helps increase user engagement, to turn that app into an engine of fan involvement and interaction.

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As for the other incidents that have beset the type over the past few months -- a fan shaft failure on an engine, an oil leak, a windshield crack -- all can safely be put down to teething problems.

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The other possibility is to increase bypass, or the amount of air the fan on the front blows past the engine.

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One way to increase the efficiency of a high-bypass jet engine is to turn the fan into an open rotor, a bit like returning to propellers, but using two rings of stubby counter-rotating blades.

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This engine uses a gearbox to allow the fan at the front and the turbine at the back to run at different, but optimal speeds.

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By contrast, the engine designs for a putative Concorde 2 had a revolutionary double-fan arrangement that would have gone a long way to cutting the noise.

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