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747-8 Manual Landing with Autothrottle to Touchdown?

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747-8 Manual Landing with Autothrottle to Touchdown?

Old 27th Feb 2022, 05:32
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747-8 Manual Landing with Autothrottle to Touchdown?

For some reason, I get asked this a lot: What will the 747-8 autothrottle do if left on during a manual (autopilot disconnected) landing?

First off, it is mandated by the FCOM landing procedure to disengage the autothrottle no later than 100 feet height above touchdown during a manual landing at my employer. This is likely because we have a mixed fleet of -8 and -400. The 747-400 autothrottle will maintain SPD flight mode annunciation all the way to touchdown, meaning it will add thrust to maintain Vapp in the flare, and usually cause a long landing if left on during a manual landing, verified in the simulator. Additionally the FCTM recommends disconnecting both autopilot and autothottle at 1-2 NM from the threshold or 300-600 feet above field elevation during a manual landing.

Does anyone know what the 747-8 will do with the autothrottle in the event that a pilot forgets to turn them off, or intentionally leaves them on during a manual landing for some reason? I am told that the -8 will retard the thrust levers to idle at approximately 25 feet, similar to an autoland, but I do not have a 747-8 simulator to try it out in. I supposed I could try it in the differences trainer, but I have low confidence in its accuracy.
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Old 28th Feb 2022, 03:57
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Directly from the FCOM: During a manual landing, if the active pitch mode is either VNAV PTH, VNAV SPD, V/S or G/S, the AT will retard the throttles to idle starting at 25ft RA. This will not occur when the pitch mode is TO/GA or FLCH.
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Old 28th Feb 2022, 04:48
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Originally Posted by STBYRUD
Directly from the FCOM: During a manual landing, if the active pitch mode is either VNAV PTH, VNAV SPD, V/S or G/S, the AT will retard the throttles to idle starting at 25ft RA. This will not occur when the pitch mode is TO/GA or FLCH.
Thanks! That answers it.
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Old 28th Feb 2022, 08:32
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Same in basically all Boeings isn’t it?
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Old 28th Feb 2022, 09:30
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Originally Posted by ACMS
Same in basically all Boeings isn’t it?
During autoland, yes, but not during manual landing. The fact that the 747-8 will retard throttles automatically if auto throttles are left on during a manual landing is a difference from the -400. The -400 remains in SPD autothrottle FMA and will advance thrust during flare to maintain target speed if the autothrottle is inadvertently left on (it is supposed to be off for manual landings).
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Old 28th Feb 2022, 11:31
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The -8 is perfectly fine to land with the AT on, it functions just like the 777.

The 400 will attempt to maintain SPD as said above, it will advance the thrust during the flare, if overridden manually to idle and the aircraft touches down there’s a rapid (1/2sec) mode change SPD to IDLE and immediate AT disconnection and the AT motors stop driving with associated master caution. Not worth the effort and distraction.

Unconfirmed reports that a update for the 400 AT to function as per -8/777 is available at a cost 💲
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Old 3rd Mar 2022, 01:24
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Auto idling at 25' RA in manual flight was a production option on the -400 and can also be retrofitted with an FMC OPC update, works exactly the same as the -8.

We have a couple with this enabled, I don't think many operators ever took it up though.
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Old 7th Mar 2022, 07:34
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On the -400 can you put the A/T into hold mode to prevent it from doing that?
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Old 7th Mar 2022, 07:41
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I agree with CCA.

747-8's A/T system can be flown like the 777, with A/T used for the landing. The -400 generally can't however it is a customer option for about US$50k a pop.
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