The devices often serve as a backup in case the electrical systems and radio in the aircraft are inoperable.

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The company hired replacement workers on Saturday to fill in for the strikers, who belong to the Aircraft Mechanics Fraternal Association (AMFA), unveiling a backup plan it had quietly drafted 18 months ago.

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Data come from multiple sources on board aircraft, in case one fails, and multiple computers run together on the ground to provide backup.

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