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When to disconnect auto throttle before landing

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I did a search on "retard" in the FCOM and found only that it retards at 27 ft AGL when A/P is active and in approaching flare mode.  I think it is part and parcel of the flare maneuver done by A/P.

 

Come to think of it, I've never tested it because I automatically retard throttles when I'm hand flying my approaches... good question.


Dan Downs KCRP

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Outside of a dual channel autoland approach, they should only go into retard during a vnav descent or lvl change descent. Unless I missed something


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According to the AA pilot on here, it does just what the autoland function does. I've never tried it real life since it's not SOP for my outfit.


Matt Cee

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If the A/T mode is MCP SPD the throttles will retard at 27' RA on the approach, it does not matter if the autopilot is on or off.

 

On a NON-ILS approach the A/T will go into ARM when you pass the RWxx waypoint at the runway threshold or the MAxx waypoint if the missed approach is prior to the runway threshold.  In this case the throttles will not retard because the A/T mode is not MCP SPD.  You would need to manually retard the throttles in this case.  A technique we are taught when flying a NON-ILS with the missed approach prior to the threshold is to select V/S just prior to the MAxx waypoint if you have the runway in sight.  This will put the A/T back into MCP SPD and allow the autothrottles to control the speed up until RETARD is commanded.

 

On a visual approach if your A/T is MCP SPD it will retard.  Depending on what you have set up in the box on a visual you may get a VNAV disconnect that will kick the A/T into ARM.  If it does that you don't get the RETARD mode.


 

 


Outside of a dual channel autoland approach, they should only go into retard during a vnav descent or lvl change descent. Unless I missed something

 

Anytime you descend through 27' RA on an approach and the A/T mode is MCP SPD they are going to go into retard.  We don't fly dual channel approaches and they retard just fine.


 

 


Do I have to select APP to get this function or did I miss anything else?

 

The retard behavior in the NGX does not seem to match the real airplane.  The sim seems to tie the retard function to the APP mode, the real plane it's a function of the A/T being in MCP SPD.


Joe Diamond

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Learned something new today then, thanks for that :). I've never had the A/T engaged below approx 200 feet, so I didn't know it did that outside of autoland :P


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My understanding is

 

MANUAL LANDING; at some point during the landing phase, the autopilot will be engaged so the PF can have manual control and hand flown. But it is possible to hand fly with the autopilot off and the autothrottle still engaged ( But most companys will not allow this) on the other hamd it certainly normal practice to disengage the A/P and A/T at the same time and hand fly the approach and landing manually.

 

 

AUTOLAND; For an AUTOLAND procedure my understanding is the Autopilot and A/T remain engaged and during the rollout, the autothrottle will automatically retard the thrust levers to idle! But the exact procedures are dependant on company to company and will vary. Also each aircraft is different.


Vernon Howells

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MANUAL LANDING; at some point during the landing phase, the autopilot will be engaged
You mean disengaged don't you?

Michael Cubine
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As previously posted, the A/T retards the thrust levers to IDLE at 27' radio, as signalled by the #1 radio altimeter. The A/T will completely disconnect 2 seconds after touchdown.


Doug Boynton

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It's been a while but today I can confirm the NGX Autothrottle is indeed not behaving as in the real plane (referencing Joe). First, I did a manual ILS approach with NAV1 and NAV2 tuned to the ILS frequency. Flight directors were off, Autothrottle set to maintain MCP Speed. Captain's and FO's course knobs tuned to the the correct course.

I was as low as 8 feet RA and nothing. At this point (actually at 27 feet) the autothrottle should have retarded. So I did a go around. 2nd time everything the same except that I this time had VNAV, LNAV and CMD A selected. Then APP mode was selected and then CMD B as well. At 500 ft I disconnected the autopilot, autothrottle still on, maintaining MCP Speed. And then as expected...autothrottle went into RETARD. So to conclude, the APP mode in the NGX needs to be selected first to have the autothrottle automatically retard.

 

 

Hans Hjorth


Hans Hjorth

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in the PMDG 777 the A/T button does not disengage when I disconnect the AP. If we want to disengage the A/T, is it the ARM A/T switches?


AMD Threadripper 1950x 16 core, 32GB of RAM, SSD, Liquid Cooled. 

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in the PMDG 777 the A/T button does not disengage when I disconnect the AP. If we want to disengage the A/T, is it the ARM A/T switches?

Uh, you realize this is the NGX forum?  The A/T is not supposed to disengage when disengaging A/P.  Program a keystroke to the PMDG keycommand for A/T disconnect in either NGX or 777. Hope this helps,


Dan Downs KCRP

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Hadn't it been said that the NGX won't idle or disconnect A/T upon landing unless you select APP mode first?  I swore I've seen a couple threads whereby users couldn't get the A/T to disconnect on hand-flown landings until they couple the ILS then disconnect the AP. 


- Chris Jefferies

 

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Maybe, not sure of the circumstances.  I have flown many non precision approaches where I disconnect A/T before landing.  However, since I am shooting a GPS or RNP approach I am in APP mode but it has nothing to do with ILS.  I can't imagine disconnecting A/T never working..., of course, it must be manually disconnected unless you are flying a coupled precision approach.


Dan Downs KCRP

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