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B744 Autothrottle on Manual Landing

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B744 Autothrottle on Manual Landing

Old 3rd Apr 2016, 10:45
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B744 Autothrottle on Manual Landing

I was going through an old study guide and read something that I was not aware of with regard to the autothrottle. It may not even be true, but I was hoping to get some feedback here on the forum:

If rejecting the landing below 5’: Manually set GA thrust and pitch to the go around attitude. Once the climb has started, push TO/GA to re-establish GA thrust and flight director commands.

With the autopilot off, the autothrottle goes off at 5’.
If rejecting, manually select GA thrust by moving the thrust levers forward and push the TO/GA switch when back above 5’ to reconnect the autothrottle.
Any thoughts on what they mean by "off"? Is this idle or does it just go into a type of HOLD submode where it stays where it was? This is theoretical, but what if you did a manual landing with the autothrottles engaged but never used reverse? Would the A/T attempt to maintain the MCP speed on rollout while you were braking?

I have never left the A/T engaged all the way to touchdown on a manual landing, so I would have never discovered this. I always thought that it was the reversers that disengaged the A/T if left on during a manual landing, but perhaps the autothrottle behavior on an autoland is different than on a manual landing.

It would make sense that the autothrottles would be affected because TOGA is disabled any time you are less than 5' for more than 2 seconds. Maybe that's why TOGA is disabled -- because the autothrottles are off?

Thanks.
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Old 3rd Apr 2016, 13:11
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This is from a current 744 FCOM:

Flare

The flare maneuver brings the airplane to a smooth automatic landing touchdown. The flare mode is not intended for single autopilot or flight director only operation.

Flare arms when LAND 3 or LAND 2 annunciates. At approximately 50 feet radio altitude, the autopilots start the flare maneuver. FLARE replaces the G/S pitch flight mode annunciation.

During flare:

at 25 feet radio altitude, the autothrottle retards thrust levers to idle
IDLE replaces the SPD autothrottle flight mode annunciation
at touchdown, the FLARE annunciation no longer displays, and the nose lowers to the runway.

Rollout

Rollout provides localizer centerline rollout guidance. Rollout arms when LAND 3 or LAND 2 annunciates.

At approximately five feet radio altitude, rollout activates. ROLLOUT replaces the LOC roll flight mode annunciation.

The autopilot controls rudder and nose wheel steering to track the localizer centerline.
During rollout, autothrottle IDLE mode remains active until the autothrottle disconnects with thrust levers in reverse.

Rollout guidance continues until the autopilots are disengaged.

Note: Ten seconds after reverse thrust levers are down, autothrottle is armed until flaps are UP. Pushing a TO/GA switch while the autothrottle is armed activates the autothrottle in THR REF mode.
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Old 3rd Apr 2016, 20:27
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Thanks for the reply, Eckhard, but you are describing the autoland. You won't get those FMA indications like FLARE and ROLLOUT on a manual landing.
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Old 3rd Apr 2016, 22:59
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Been a while, but I suspect they are alluding to the fact that in that scenario (more than 2secs below 5' ??) you will have to push the thrust levers up manually. A subsequent push of the a TOGA button will re-connect the autothrottle.
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Old 3rd Apr 2016, 23:15
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A subsequent push of the a TOGA button will re-connect the autothrottle.
But only if you are above 5'.
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Old 3rd Apr 2016, 23:37
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Correct! Hopefully the GA is going well enough at that point for that to be the case . . .
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Old 3rd Apr 2016, 23:57
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So we both agree that below 5' for more than 2 seconds disables (for lack of a more descriptive word) the A/T for purposes of TOGA.

The question I have is on a manual landing, what is the effect of this disabled state? Below 5' for 2 seconds would likely be right after you touch down. If you didn't use reverse, would the A/T feed in power as you braked the a/c on rollout? Would it go to idle? Or would it just stay at whatever setting it was when the A/T became disabled? What would be displayed on the A/T FMA? Would it stay in SPD?
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Old 4th Apr 2016, 00:47
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Once disabled it will stay where it is, but you should be retarding thrust to idle in the flare and selecting idle reverse thrust as a minimum for a full stop landing. Suggest you look out the front for a manual landing rather than looking at the FMA annunciations.
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Old 4th Apr 2016, 01:03
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Suggest you look out the front for a manual landing rather than looking at the FMA annunciations.
Like you, I have made all my manual landings looking out the front. That's why neither of us knows exactly what is going on with the A/T at that point (e.g., Does it go to idle or hold? Does the FMA blank? I don't know). As I said, this question was theoretical and I am at least willing to admit that I don't know; thus, my question for someone who does.

Thanks anyway.
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Old 4th Apr 2016, 03:06
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I've always referred to this as the "TOGA Dead Zone."

You can click the button but it ain't gonna work.

So build the habit of advancing the levers *every* time on go around and *then* click TOGA. You'll never go wrong.
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Old 4th Apr 2016, 03:28
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With the autopilot off, the autothrottle goes off at 5.
Interesting to know. There is certainly nothing in maintenance manuals about this.

I doubt the thrust levers would go into idle, however. Without cues from the FMC or A/P, the A/T must surely go into a hold mode for safety. Having said that, the 737NG has a flare thrust lever retard mode at 27' RA if the A/P is not engaged (with the aircraft on the ILS and flaps extended). The NG A/T disconnects 2 seconds after touchdown.

I assume in the absence of a valid Rad Alt signal, the A/T would remain in SPD mode.
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Old 4th Apr 2016, 09:51
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I've always referred to this as the "TOGA Dead Zone."
I am aware of the dead zone, but I never questioned the reason for it. Could it be that TOGA doesn't work below 5' because the throttles are disabled for manual landings? What other reason would Boeing disable TOGA in this area?
Having said that, the 737NG has a flare thrust lever retard mode at 27' RA if the A/P is not engaged (with the aircraft on the ILS and flaps extended).
I think the 777 also disengages at around 25' for manual landings.
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Old 4th Apr 2016, 11:36
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With the autothrottle armed (MCP) and no autopilot or autothrottle engaged, with 3 or 4 engines, normal EEC mode, the autothrottle remains ARMED (available for a 'controlled' 2000 fpm climb) until 2 secs after 5'R (when the TOGA switches are inhibited) until 3 secs after 5'R in the climb. If there is no valid radalt signal presumably the inhibit doesn't occur?
So, as I understand it, the AT remains armed throughout but the TOGA switches themselves are effectively unpowered.

Not sure if that answers your original question. It's been a while......
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Old 4th Apr 2016, 17:12
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Basically, below 50' radar altitude the automation is configuring itself for the flare and roll out.

Flare begins at 50'. FMA changes from G/S to FLARE.
Between 30-15' Thrust goes to idle. FMA changes from SPD to IDLE

At 5' TOGA is disabled and FMA LOC changes to ROLLOUT

At touchdown FMA FLARE goes blank and nose is lowered to runway, spoilers should deploy and once the thrust reversers are deployed you're essentially committed to the landing.

The above is mostly a summary from a company training document.

I think the design essentially puts the burden on the pilot to MANUALLY begin the go around procedure at such a LATE POINT in the landing maneuver. The automation is busy preparing for the roll out portion and while it will not block the manual advancement of the power levers, neither will it be done automatically--remember below 5' it's transitioning to ROLLOUT with IDLE thrust.

Hope that clarifies it a little.
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Old 4th Apr 2016, 21:17
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So, as I understand it, the AT remains armed throughout but the TOGA switches themselves are effectively unpowered.
Percy: Then you are saying that the A/T will attempt to maintain the MCP speed upon touchdown on a manual landing if no reverse is used?

remember below 5' it's transitioning to ROLLOUT with IDLE thrust.
Zero: You are describbing an autoland and that is completely different than a manual landing. There is no FLARE, IDLE or ROLLOUT on a manual landing.
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Old 4th Apr 2016, 22:21
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Percy: Then you are saying that the A/T will attempt to maintain the MCP speed upon touchdown on a manual landing if no reverse is used?
I'm pretty sure Percy is saying that the A/T will not do anything (as your books say)

There are a couple of not-so-cheap desktop flight simulators on the market which model an active SPD mode during non-A/P coupled rollouts, but I would be more inclined to believe your FCOM.

Last edited by NSEU; 4th Apr 2016 at 23:35. Reason: Grammar
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Old 4th Apr 2016, 23:04
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No. The autothrottle is not engaged, so the thrust & levers will stay where you put them.
The A/T is ARMED so it's available for TOGA except when the TOGA switches are inhibited.
Which is from 2secs after 5' on descent until 3secs after 5' in the climb!
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Old 4th Apr 2016, 23:12
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I'm pretty sure Percy is saying that the A/T will not do anything (as your books say)
Well, if you are now speaking for Percy, then maybe you can explain how the A/T can "remain[] armed throughout" but the "A/T will not do anything."

My books don't address this issue, as I'm sure yours don't either or you would have an answer.

To simplify the question: If you do a manual landing with the A/T engaged and you do not use reverse, will the A/T attempt to maintain the MCP speed on rollout? According to Percy, if the A/T is armed, then when the speed starts to bleed off on the rollout the A/T will advance power to maintain the MCP speed.

Last edited by cf6-80c2b5f; 5th Apr 2016 at 00:55.
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Old 4th Apr 2016, 23:35
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My mistake. I didn't register the contents of his second sentence. All I saw was

"the autothrottle remains ARMED (available for a 'controlled' 2000 fpm climb) until 2 secs after 5'R"

Your books say something similar, ergo my comments

My books don't address this issue, as I'm sure yours don't either or you would have an answer rather than being nonresponsive.
Nonresponsive? My first post said that your comment was interesting to know and told you that my books lacked that information. I thought I was being supportive, not nonresponsive.

Last edited by NSEU; 4th Apr 2016 at 23:51.
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Old 4th Apr 2016, 23:46
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None of the Boeing or company manuals I have addresses my question. That's why I'm throwing it out here in hopes that someone might know. Granted that landing without using at least idle reverse is not something I've ever done, nor would I recommend it.

I'm just curious whether the A/T would attempt to maintain MCP speed on the rollout during a manual landing if no reverse is used. If it does, the A/T FMA would probably stay in SPD mode.

If the A/T does not attempt to maintain the MCP speed on rollout, then what mode is it in, and when did it get there? At 5', as one study guide suggests? I don't know.
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