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RISCfuture

ETOPS flights and ADIRU re-alignment

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Hello pilots! I'm doing my first multi-leg ETOPS flights in the 777 and I had a question for y'all. I landed after a transpacific flight and set up for the turn so I could fly back across the other way. Before takeoff though, I noticed that my ADIRU had a ~10-nautical-mile inaccuracy. I know this is typical for an inertial navigation system, but I also read that per transoceanic procedure, you shouldn't enter an oceanic leg unless your navigation system error is within acceptable tolerances. Obviously thanks to the GPS and DME-DME my total ANP was still ~0.06, but if my GPS were to fail over the ocean I wouldn't be able to navigate effectively anymore. Is there a procedure that pilots do during a short turn to reset accumulated ADIRU error? Or do they just power-cycle the ADIRU?

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Is there a procedure that pilots do during a short turn to reset accumulated ADIRU error? Or do they just power-cycle the ADIRU?

 

Even a short turn is going to be longer than required to reboot the ADIRU.  I always turn them off when I am doing my after on the blocks checks.  They get turned on when the new copilot arrives in the cabin, or in my case when I start preparing for the next flight.  The units are usually ready for setting coordinates before the fuel and catering tasks are done.

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For what it's worth, I think the FCOM says that if the aircraft is stationary on the ground long enough, the ADIRU will automatically realign... but I think best practice is to manually realign it by turning it off for a while and turning it back on when you're running through the preliminary preflight procedure.

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