B744 Autothrottle on Manual Landing

[cf6-80c2b5f]

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.

[eckhard]

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.

[cf6-80c2b5f]

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.

[esreverlluf]

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.

[cf6-80c2b5f]

A subsequent push of the a TOGA button will re-connect the autothrottle.

But only if you are above 5'.

[esreverlluf]

Correct! Hopefully the GA is going well enough at that point for that to be the case . . .

[cf6-80c2b5f]

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?

[esreverlluf]

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.

[cf6-80c2b5f]

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.

[zerozero]

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.

[NSEU]

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.

[cf6-80c2b5f]

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.

[Percy Cute]

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......

[zerozero]

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.

[cf6-80c2b5f]

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.

[NSEU]

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.

[Percy Cute]

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!

[cf6-80c2b5f]

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.

[NSEU]

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.

[cf6-80c2b5f]

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.

[Capt Quentin McHale]

cf6-802b5f


"With the autopilot off, the autothrottle goes off at 5’."


A very interesting scenario indeed. I'm thinking misprint, and it should read... the autothrottle disengages (but remains armed) at 5' RA. Perhaps a B744 Avionics engineer could throw some light on this. Any out there?


McHale. :)

[NSEU]

Granted that landing without using at least idle reverse is not something I've ever done, nor would I recommend it.

Your hypothetical scenario also assumes that you haven't manually brought the thrust levers to idle during the flare. If you have, then we get into the area of dormant servomotors due to manual intervention.

From the BAMM
"(h) The *control A/T servo is responsible for throttle rate servo command, manual override detection and line voltage compensation.
1) Manual override occurs when the throttle rate does not track the commanded servo
rate. This may be caused by the pilot manually opposing the A/T lever motion or the
levers reaching their physical position (?**). Whatever the cause, the control A/T servo will
detect it and cause the throttles to become dormant."

(EDIT) This statement, too, is somewhat ambiguous. Does the A/T servo only become dormant while you are opposing the command, or does it put the A/T servo permanently "on hold".

*The "control A/T servo" is actually a control function within the FMC and not the A/T servomotor itself
** Did the author mean "physical limit" rather than physical position?

[Capt Quentin McHale]

"maybe you can explain how the A/T can "remain[] armed throughout" but the "A/T will not do anything."


Flaps in landing configuration, aircraft in ground mode (WOW...weight on wheels) perhaps. Just my two cents worth.


McHale. :)

[cf6-80c2b5f]

Correct, NSEU -- No need to throw that into the mix too. For the hypothetical, we just won't select reverse at all.

Manual override occurs when the throttle rate does not track the commanded servo rate. This may be caused by the pilot manually opposing the A/T lever motion or the levers reaching their physical position. Whatever the cause, the control A/T servo will detect it and cause the throttles to become dormant.Not to change the subject, but this sounds like what would occur when in FLCH (either climb or descent) and you manually override the throttles. They will go to HOLD, just as Asiana in SFO discovered when they manually overrode the throttles and pulled them back to idle after pressing FLCH at 1600'.

I'm curious, does your BAMM state whether this throttle rate is a specific TLA or a specific period of time that it diverges from the commanded servo rate, or both? I have read the figure 1.3 seconds to set it into HOLD during a FLCH climb or descent, but I have also read that movement of more than one throttle knob-width will do it. Maybe I should make a separate post for this.

[NSEU]

Sorry, there is no mention of the rates or distances in the maintenance manual for manual override.

A separate post for this might be a good idea considering the ambiguities found in the manuals for this subject: e.g. looking at an old AOM for one particular airline, I see the following statement ...

"Thrust levers can be manually positioned without disconnecting the autothrottle.
After manual positioning and release, the autothrottle repositions thrust levers to
comply with the active mode. The autothrottle system does not reposition thrust
levers while in HOLD mode."

If moving the levers produces HOLD mode, then how can the levers reposition?

[cf6-80c2b5f]

FLCH is a special situation. When the throttles are manually overridden in FLCH, or they automatically reach the idle stop on their own (for an idle descent), the FMA will indicate HOLD and the throttles will not re-activate if the speed gets slow (unless or until you reach the MCP altitude you are heading for -- then they will go to SPD||ALT).

[This is assuming the A/P is disengaged].

[cf6-80c2b5f]

"With the autopilot off, the autothrottle goes off at 5’."

A very interesting scenario indeed. I'm thinking misprint, and it should read... the autothrottle disengages (but remains armed) at 5' RA. Perhaps a B744 Avionics engineer could throw some light on this. Any out there?I don't know if it's a misprint. I think that since TOGA is disabled below 5' for 2 seconds, there is also something that affects the A/T at this point. Or, maybe TOGA is disabled precisely because the A/T is disabled.

[NSEU]

FLCH is a special situation. When the throttles are manually overridden in FLCH, or they automatically reach the idle stop on their own (for an idle descent), the FMA will indicate HOLD and the throttles will not re-activate if the speed gets slow (unless or until you reach the MCP altitude you are heading for -- then they will go to SPD||ALT).

Which means the quote in the old AOM I have is quite wrong (Who writes these things?)

[cf6-80c2b5f]

I don't think it's wrong -- it just doesn't explain it very well. If you are descending in SPD mode on the A/T (say SPD||V/S) and you manually override the throttles by pulling the power back, the throttles will just go back to maintaining the select speed when you let go of them.

But if you do that while in THR||FLCH SPD, the A/T goes to HOLD||FLCH SPD and the power will not move back when you let go of the throttles.

[Percy Cute]

CF6: I think I've caught your drift now. What you are asking is:
On a manual approach (or if you're daft enough, using V/S and one autopilot! But anyway, without arming FLARE mode) WITH the A/T engaged, when you close the thrust levers to idle against the demand of the servo, will the T/Ls always move forward again to maintain your selected Vref? Or perhaps after 5'R plus 2 secs (or WOW squat switch?) will they remain closed?
Simple answer: Don't know.

[cf6-80c2b5f]

Exactly! That makes at least two of us who don't know. Thanks.

[cf6-80c2b5f]

Very good!. Thanks! This largely confirms what I am hearing from someone who just tried it in a sim. I would have bet that the A/T would disconnect on manual landing at least by touchdown if not by 5', but not that you would see IDLE at 25'. This is interesting. Is this based on observations in the sim, airplane or both? Thanks again.

[cf6-80c2b5f]

If your 744 manuals even mention a distance (15' or 25') they are miles ahead of anything I can find. I sure would like to see something on this in writing if it's not too much trouble. So, you are pretty sure the -8 A/T works the same as the 744 in this regard? I know the -8 has A/T wakeup when disengaged and the 744 doesn't, but I don't know that it would necessarily affect the scenario above.

[cf6-80c2b5f]

Thanks. Just to be sure we are both on the same sheet of music -- and I think we are -- this is for a manual landing (without the autopilot). I'm pretty sure that's what you mean. If so, your manuals must be spectacular. I haven't seen that figure anywhere.

[cf6-80c2b5f]

PS: the 777 and Airbus kids must be laughing at this thread.
Manual thrust, wtf is that???

When I transitioned from the DC-8 to the DC-10 back in 2000 the A/T was a novel feature -- It actually worked on every airplane. Imagine that.

[cf6-80c2b5f]

After landing he was thrilled and said it was the most fun he had ever had........which is equally sad.

Yes, it is.

[cessnapete]

Why would you have the A/T in use on a manual landing. Surely a manual landing is just that no A/P no A/T. On the B744 in my Company use of A/T was not recommended on a hand flown approach.

[cf6-80c2b5f]

I am not advocating use of the A/T on a manual landing. As I said in my first post, this is theoretical. I eventually got my answer.

Incidentally, the Asiana crew in SFO never planned on pressing FLCH inside the outer marker, nor did their manual authorize it; but they found themselves in that situation one summer day in 2013. If they had better understood how the airplane would behave, perhaps they could have averted the outcome. I thought that's what this tech forum was for.

It is interesting that you ask this type of question. Almost five years before the Asiana crash a poster asked a theoretical question about the 777 A/T trap that caused the Asiana crash. You can read the post here, http://www.pprune.org/tech-log/342579-777-flch-climb-t-going-into-hold-no-low-speed-prot.html but I'll save you the time and share the replies to his honest question below. Cheers.

Why would you want to climb , holding back the thrust levers ? Good one fourgolds! Why would you hold the thrust levers closed in climb, FLCH or otherwise, and let it get into a lowspeed situation, and then not advance them to get out of it?God help all of us all if you are practicing this on the paying-public in open and shared skies in one of the shareholders aircraft. And I have to echo the theme why climb with no thrust, doesn't seem that sensible. Why would you pull the thrust levers back against the A/T even if ATC said stop climb now????????????????????? Maybe we need 'low speed pilot detection' If you're a real pilot flying real airplanes, I hope that I won't ever be paxing on your airplane. Because you are a busybody; perhaps overly bored sitting in the cockpit for hours doing nothing, who constantly needs to dabble with systems, . . . pulling the throttles back in a climb . . . like a mechanic who needs to fix something that isn't broken. While you at it why don't you try a barrel roll too:ok: The A/C FBW will object BUT you could still do it with your flying skill I'm sure!!

[Bunk-Rest]

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.

Irrespective, do you think Boeing would have not thought of this in the system design?
Do you think that this might happen?
Are you really flying 747's ?

[cf6-80c2b5f]

Irrespective, do you think Boeing would have not thought of this in the system design?
Do you think that this might happen?
Are you really flying 747's ? It's hard to tell whether you are being sarcastic or just daft. Do you think Boeing would have not thought to provide better warnings about the FLCH trap?

Irrespective, if the original question was so intuitive to everyone, it would not have taken five days to find someone with the answer. I don't recall your making any substantive contribution during that time, but if you have something constructive to say on this question, I invite you to share it.

[NSEU]

Irrespective, do you think Boeing would have not thought of this in the system design?
Do you think that this might happen?
Are you really flying 747's ?

I didn't know the 744 did this either (as a former Avionics Maintenance Engineer). My maintenance training notes tell me that the command to idle the thrust levers during Autoland comes from the AFDS system. Would you so readily assume that the command also happens with the AFDS disengaged if you had no previous Boeing experience?

I made an earlier comment on the 737NG about its thrust levers going to idle at 27' with the A/P not engaged (but the aircraft on the ILS) because I thought it different from the 744. Apparently it's not. The training notes for the 737NG and the Maintenance Manual are much clearer in this respect. The signal path and logic is shown in diagrams. The text tells you what happens.

There are lots of things on the 744 and other Boeing aircraft which go against intuition.

[BBK]

CF6

I think it's great that people can post questions and discuss the answers. I'm always ready to learn which is why I read this thread so nothing wrong with that.
However, your question was, in my humble opinion, not so much hypothetical but unrealistic. You may disagree but I'll explain my reasoning.

On a manually flown approach my company always recommends disengaging the autothrust. I don't think it's prohibited as such but the pitch power couple makes it clumsy so no autopilot then we use manual thrust. In fact with the CF6 and metric weights it's a easy to remember the power setting as it's 6 plus the middle digit of the weight eg 240 tonnes use 64%. Add about 8% so 72% if one engine inop. Useful info every 6 months or so!

I'd never thought about it but yes I suppose if, contrary to the recommended technique, one left the autothrust (A/T) engaged then perhaps it will still retard the thrust in "idle" mode at about 25 ft radalt. Of course that's one of the cues one looks for in an autoland along with "flare".

I'd never heard of FLCH trap until the Asiana crash and as someone else mentioned it might be an issue on the 777 and 748 but not the 744 although I'm happy to be corrected but it doesn't ring any bells and I've read the FCOMs a few times.

If there is a trap of sorts then it's the fact that TOGA as a mode is not available after a prescribed time and height - 5 radalt and 2 seconds? While I remembered that in the context of an autoland it surprised a colleague who rejected an approach very late, the classic "floater", then realised hitting TOGA wouldn't work. No problem once he realised of course back to basics. There but for the grace of God!

Hope that helps.

BBK

[atpcliff]

My airline is two merged. One of the two would always turn off the AT on a hand flown approach, the other would always leave the AT on during hand flown. I now do both of the above, plus sometimes leave both on, until very late, or auto land. If I am using AT on during hand flown, I turn it off at about 50', just before I retard the throttles.

I like using the AT during gusty conditions...it keeps the plane from getting too fast. It is slow in advancing thrust, so if the plane starts to get slow I manually push the throttles up a bit. I find this much less of a workload in gusty conditions than manual throttles.

Also, at my airline, we were all taught that the AT would maintain min safe speed in all conditions. We didn't know about this AT slow speed trap that caught Asiana until their crash. It was not in our publications. Our check airman tried the Asiana situation in the sim and were surprised that the airspeed was not maintained.

[Intruder]

In gusty winds I MUCH prefer to use manual thrust. Autothrust does not respond well to gusts in all airplanes, and I find it easier to simply allow the airspeed to vary a bit around the bug speed, resulting in a more stable approach. After all, that IS why you increase the bug speed for gusts, isn't it?

[Bunk-Rest]

With flaps out of up, but not in landing position, activation of VNAV in VNAV PTH
changes the reference thrust limit to CRZ. However, pressing TO/GA changes the
reference thrust limit to GA and GA thrust is available.
Pushing either TO/GA switch activates a go-around. The mode remains active even
if the airplane touches down while executing the go-around.
When the flight director switches are off, pushing either TO/GA switch displays the
Flight Director Bars.
An automatic go-around cannot be initiated after touchdown.
Note:
An automatic go-around cannot be initiated after touchdown or if the aircraft
is below 5 ft radio altitude for more than 2 seconds.

Now I would have thought that the implication of that was that the auto throttles are closed and will not re-open.

It also would seem obvious that the automatic go-around functions if the autopilot is in or out, and/or the auto throttle is engaged/disengaged.

Why would you imagine that the auto throttle would try to maintain the selected speed during the ground roll?

[Capt Quentin McHale]

cf6,


Firstly I must thank you for starting a very good thread. It has produced many a theory on the AT system. Some on the money, some close and some nowhere near the ballpark so to speak.


Anyhow after much digging around and harassing some of our engineers, I may have had a "Eureka" moment. So here's my two cents worth.....


On approach at 25ft RA the AFDS sends a flare retard signal to the AT and causes the AT servo to drive the throttles to the aft stops (interestingly this happens during a MANUAL or AUTO landing). SPD will be replaced by IDLE on the FMA.


At <5ft RA TOGA is inhibited (but AT is still armed) until >5ft RA or reverse thrust selected (and AT disarmed). If you do not select reverse thrust and use only braking, the AT mode will remain at IDLE and will not resume the SPD mode.


For the SPD mode to engage several conditions must be met. These are....
- AT armed
- AIRCRAFT IN THE AIR>400ft
- Thrust limit mode not takeoff
- Go-around mode not active
- FLCH mode not active
- VNAV mode not active
- G/S mode not active
- Select SPD mode on MCP or
- Default SPD selection, for example, exit of FLCH or VNAV.


Hope this helps.


McHale.

[cf6-80c2b5f]

Thanks for the input, Captain.

On approach at 25ft RA the AFDS sends a flare retard signal to the AT and causes the AT servo to drive the throttles to the aft stops (interestingly this happens during a MANUAL or AUTO landing). SPD will be replaced by IDLE on the FMA.It is interesting. None of my books says anything about how the A/T will behave during a manual landing. During a manual landing, as you know, you are not going to see the FLARE at 50' or the ROLLOUT at 5' on the FMA. If there's no FLARE and no ROLLOUT then I think it would be a stretch to imply that it would "seem obvious" that the AFDS would be sending a flare retard signal to the A/T servo to drive the A/T to IDLE. Nevertheless, this must be taking place behind the scene, even in the absence of the FLARE and ROLLOUT commands.

If you have any material on this and it's not too much of a burden, please PM me with it. Thanks again!

[Capt Quentin McHale]

cf6


Have sent PM (hopefully)


McHale.

[NSEU]

If there's no FLARE and no ROLLOUT then I think it would be a stretch to imply that it would "seem obvious" that the AFDS would be sending a flare retard signal to the A/T servo to drive the A/T to IDLE.

Ditto


On approach at 25ft RA the AFDS sends a flare retard signal to the AT and causes the AT servo to drive the throttles to the aft stops (interestingly this happens during a MANUAL or AUTO landing). SPD will be replaced by IDLE on the FMA. At <5ft RA TOGA is inhibited (but AT is still armed) until >5ft RA or reverse thrust selected (and AT disarmed). If you do not select reverse thrust and use only braking, the AT mode will remain at IDLE and will not resume the SPD mode.


Thinking about the finer details... Do we know if IDLE would be annunciated on the FMA for A/T during rollout in this hypothetical scenario? Assuming the levers reach the aft stops before the aircraft reaches 5' plus 2 seconds, would the A/T go into HOLD mode (annunciated/not annunciated)?

Is the A/T system both inhibiting the TO/GA switches and putting the system into a hold mode where manual manipulation of the thrust levers is not opposed?

[cf6-80c2b5f]

Do we know if IDLE would be annunciated on the FMA for A/T during rollout in this hypothetical scenario? Assuming the levers reach the aft stops before the aircraft reaches 5' plus 2 seconds, would the A/T go into HOLD mode (annunciated/not annunciated)?

I can only go by what the A/T does when in autoland. If manual is the same as autoland, there is no HOLD.

What is not clear to me is when the A/T actually goes from IDLE to blank.

Is it:

1. At touchdown;
2. When less than 5'RA;
3. When less than 5'RA for >2 seconds; or
4. When reverse is applied?

I'm still looking for something in writing on this one.

[cf6-80c2b5f]

ie: there is no THR, SPD or IDLE.
The AT is "off".
The AT behaves exactly the same way for a Manual Landing with AT engaged as it does in an Autoloand.
Thanks. I'm looking at my FCOM and this is what it says under the autoland section:

During rollout, autothrottle IDLE mode remains active until the autothrottle disconnects with the thrust levers in reverse.

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. Could there be a software revision or specific airline setting that would account for the disparity?

[CCA]

Having just done two manual landings in a 744ERF with a NGFMC I can tell you it stayed in SPD until just AFTER touchdown (as in not immediately on touchdown) the FMA went blank and an EICAS >AUTOTHROTTLE caution resulted.

I had to manually override the servo motors during the flare until it self disconnected, I then cancelled the caution with the thumb switch (didn't need any surprises) and selected reverse.

[cf6-80c2b5f]

Having just done two manual landings in a 744ERF with a NGFMC I can tell you it stayed in SPD until just AFTER touchdown

Well this totally throws a monkey wrench into the spokes! Thanks for the feedback CCA. Looking forward to hearing Silberfuchs' experience.

[NSEU]

According to one source, this behaviour is backed up in the simulator. i.e. no idle during flare with the A/P not engaged. Manual intervention required.

[Willit Run]

Manual is manual; auto is auto. Do NOT mix the two.
If you truly feel the airplane speed control can do a better job than you can, you are already behind the eight ball. The speed control on the 744 sucks! The systems are logically good, but the automation is geared for the lowest common denominator.

[cf6-80c2b5f]

Still hoping to hear from Silberfuchs.

[cf6-80c2b5f]

Thanks! Did this -400 have the NG software? If so, it's looking like the NG software is the reason for the IDLE at 25' versus just going from SPD to blank when below 5' for 2 seconds.

[cf6-80c2b5f]

Well, that blows my theory. I was hoping you would say it had the NG software. Thanks again for trying this, Silberfuchs.

[JammedStab]

Thanks for the thread.

I can't see that it would have been any other way. IDLE after touchdown makes sense to keep the thrust levers from adding power by holding them aft. There is no way the aircraft would have been certified if it went to SPD on touchdown. We know the autothrottle disengages at reverse selection which would of course, blank the associated FMA indication. Going to IDLE at 25 feet is exactly what it does during an autoland but thinking about it, I doubt the autothrottle has any idea how whether the autopilot is engaged or not so it just does its thing as usual.

I think that the only thing that happens below 2'(or whatever the very low altitude is after a certain number of seconds is that the TOGA switches are deactivated meaning...manual advancement of thrust levers for the go-around.

[cf6-80c2b5f]

Good to hear from you, JammedStab.

There is no way the aircraft would have been certified if it went to SPD on touchdown.It doesn't go to SPD on touchdown; what was seen in the sim was that somewhere below 5' the SPD FMA just went blank and on touchdown the throttles remained wherever they were when it blanked. I have a study guide that states the A/T will go off at 5'.

I'm just trying to figure out if some of the 744s (maybe older versions) actually don't go to IDLE at 25' as Silberfuchs experienced. I have a friend who is going to try it on a 744F in a few hours, conditions permitting, and hopefully he will report back.

[NSEU]

I doubt the autothrottle has any idea how whether the autopilot is engaged or not so it just does its thing as usual.

As I said earlier, the idle retard command actually comes from the AFDS (according to the engineering manuals). One would hope that the AFDS knew if it was engaged or not :)

Cheers

[JammedStab]

As I said earlier, the idle retard command actually comes from the AFDS (according to the engineering manuals). One would hope that the AFDS knew if it was engaged or not :)

Cheers
Thanks,

Obviously your manuals have more details than our manuals. But the real question would be, is there any difference in autothrottle operation based on the use of the autopilot and if so, why.

[cf6-80c2b5f]

That pretty much restates my original question in a more concise way. So far, we've got peole saying it behaves the same as the autoland and people saying it stays in SPD until anywhere from 25' RA to a few seconds after touchdown, then the autothrottle FMA goes blank -- no IDLE. CCA said he even got the AUTOTHROTTLE caution when it went from SPD to blank after touchdown. It is appalling that Boeing doesn't explain this better.

[BBK]

Re the Boeing manuals it's just a thought but maybe they're written to give pilots the necessary info not answer hypothetical questions?:E

[cf6-80c2b5f]

It's a "hypothetical question" until it causes an accident, like the Asian 777 in SFO. If you're happy being ignorant about this, you can always skip this string. Thanks again for your valuable input.

BTW, regarding your prior post:

I'd never heard of FLCH trap until the Asiana crash and as someone else mentioned it might be an issue on the 777 and 748 but not the 744 although I'm happy to be corrected but it doesn't ring any bells and I've read the FCOMs a few times.

This demonstrates how poorly Boeing writes its manuals. You've read them a few times and you still don't know whether the FLCH trap applies to the 744? I can tell you without hesitation that it does.

[BBK]

Two questions for you Cf6, why do want to know so badly what happens in this situation which, in my company, shouldn't occur anyway.

In your considered opinion is FLCH an appropriate mode for final approach.

rgds

BBK

PS Oh and I word searched "FLCH trap" in the FCTM and Vol 1/2 of the FCOM and no results.

PPS I believe the Asiana crash may have something to do with the aircraft's speed decaying to something like Vref minus 17!

[cf6-80c2b5f]

BBK:

I'm not sure why you feel compelled to police the forum for questions that you believe are inappropriate simply because "in [your] company, [it] shouldn't occur anyway." Really, you should probably refrain from clicking on this thread if it bothers you that much. So far, your posts have demonstrated that you have nothing of value to add to it.

Of course, FLCH isn't appropriate on final approach, but it was pressed and it resulted in a crash. Most crashes are due to something that shouldn't occur.

The "FLCH trap" was coined by the investigators and attorneys after the Asiana crash. If you did the same thing in the 744, the logic would react the same way.

[BBK]

CF6 just to refresh your mind this is what I wrote originally. I thought it was polite enough.

"I think it's great that people can post questions and discuss the answers. I'm always ready to learn which is why I read this thread so nothing wrong with that.
However, your question was, in my humble opinion, not so much hypothetical but unrealistic. You may disagree but I'll explain my reasoning......

.....Hope that helps. "

I certainly don't intend to "police" this forum or any other and I'm at a loss why you think so as I only asked why your keen interest. Just idle curiosity. I assume, from what you have written, you are not flying the 744 so thought your comment about the "appalling" Boeing manuals a little odd. I reiterate that using FLCH on the final approach is not a good idea nor is losing control due to stalling on short finals.

Anyway, I consulted said manuals and found the following:

"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

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."

I still think manual flight and manual thrust works just fine as did my trainers some of whom have flown the 400 since the 90s.

BBK

Ps exception I've just remembered might be a Cat3A with a dual FMC failure.

[cf6-80c2b5f]

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

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."

There have been reports on this thread that are contrary to the above, unless you take the first sentence as meaning that none of the description that follows the first sentence applies to a manual landing. Check out CCA's post.

I do fly the 744, but I have been out on a medical leave. As I dug into the FMC logic with time to kill, I realized how little I really knew about how it would behave under certain circumstances. When I dug further, it became apparent that my peers were equally clueless. The answers I have received on this forum confirm that it is not just limited to my peers at my airline. We have first-hand testimony from one pilot that it will go from SPD to IDLE and another guy saying that IDLE never happens -- it just goes from SPD to a blank FMA. How could there be such a discrepancy from 744 to 744 with nothing written in the manuals to explain it? Anyway, thanks for the input.

[BBK]

CF6

Just goes to show one shouldn't jump to conclusions and happy to stand corrected. On reflection I wrote my penultimate post after a long night flight so maybe it wasn't as well phrased as it could have been.

Anyway, as you will know very well there are lots of things going behind the scenes with the AFDS that are not annunciated eg runway alignment. I can't offer an explanation for the discrepancies other than maybe they're are different modification states of the FMC perhaps. When you get into how waypoints are coded in the FMC and things like "on approach logic" 'tis a dark art indeed. Anyway, anything I can add I'm sure you would know as a fellow operator so I'll leave it at that.

BBK

[cf6-80c2b5f]

Thanks, BBK. You may very well be right about the different modification states. Whether it was a delivery option from the factory or a subsequent modification, it would be interesting to know the background on this. But like you said, it's a dark art, and at this point most of the engineers who initially worked on the 744 are probably long retired.