A/T autodisconnection during manual flare

[tango4]

Apologies for the Hijack... Will do right now !

[emerydc8]

So, what are the latest facts if we refer to the BA sim?

1. When the AFDS status is "NO AUTOLAND" or "FD", the ROLLOUT and FLARE modes are not available.

2. During a "no autoland" flare, when TOGA is armed for landing (G/S captured or flaps out etc.), the A/T mode will never change from SPD to IDLE. Instead, when the aircraft is below 5 ft (+2 sec), the A/T will automatically disconnect with a caution alert and the throttles will stay at their last positions.

Hardy,

Have you taken a look at this section of my FCOM under autoland? It seems that the A/T behavior is significantly different than in manual. One conflict I see is that Peter mentioned that the sim would not go to TOGA [FLCH] on the ground with takeoff flaps set, but according to my FCOM, it will go to TOGA after landing under the conditions set forth below, even after the thrust reversers have been deployed. I'm not sure how or if this can be reconciled with all the facts we're putting together. This statement below is also in the Polar manual under the autoland section. [EDIT]: Sorry, I misread Peter's post.

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.

[Hardy Heinlin]

Yes, but it disagrees with the BA sim ...

[emerydc8]

I don't even understand the logic behind why the A/T would re-arm 10 seconds after coming out of reverse and stay armed until the flaps are up. Any thoughts on this? Peter pressed TOGA and didn't get anything but this was prior to takeoff. The note in the FCOM refers to after an autoland. Maybe that would explain the discrepancy with the BA sim. It is possible that the A/T behavior is different as compared to a manual landing, where you don't get IDLE.

[EDIT]: My mistake. This was when he pressed FLCH on the ground -- not TOGA. So, what I see keeping the throttles from going to THR REF when TOGA is pressed during taxi (A/T arm switch armed) is the flaps being up. Once the flaps are set for takeoff, I presume you would get TOGA if you pressed it. Peter mentioned somewhere that he had seen this on the line where TOGA was accidentally pressed on taxi out. On taxi in, once the flaps are up, I presume TOGA is disarmed -- at least after an autoland. On a manual landing, who knows if it would work the same as the note.

[John H Watson]

re you saying that you get ROLLOUT and FLARE even when only 1 A/P is engaged and NO AUTOLAND is annunciated? So will the AFDS still provide autoland roll and pitch commands even when just 1 or zero A/Ps are engaged?

My manuals say:

Autoland uses multi-channel autopilot for the final approach, flare and rollout. A single autopilot engaged allows approach operation through flare.

Does this mean rollout is not available?

[emerydc8]

I don't think you will see flare with only one A/P doing the ILS. It will fly it right into the runway without flaring. I don't think you will see rollout either with only one autopilot. Doesn't it just stay in LOC?

[Magoo]

You need multiple channels engaged to control the rudder on approach, which is something ROLL OUT need otherwise to maintain a track the A/C will try to bank. You notice this very well on an engine out go around from a coupled ILS, as you press TOGA, the A/P lets go of the Yaw control as you go single channel and you end up having to apply rudder yourself.

Now I spoke to a couple of colleagues regarding the A/T business. it seems BritJet is correct, the 744 A/T will not retard if the FMA isn't set up for an autoland, ie FLARE and ROLL OUT mode armed. Once the A/P is disconnected, those modes will disappear and you are left with SPEED active in the FMA and the A/T will maintain SPEED all the way to touchdown. I guess that explains why we never fly manually with the A/T active on landing!!! 

[emerydc8]

This takes us back to my original 4-page string on pprune asking what my study guide could mean by the word "off."

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.

I guess it means just that -- The FMA goes "off" (blank) and the throttles stay where they were when it happens; although there were two posters who currently fly the airplane and claim to have just done a manual landing with A/T engaged, both with differing results than above. Still waiting for further feedback from them. Thanks for the input, Magoo.

[Magoo]

The confusing thing is we fly the -8 as well and on that beast, the A/T can be left on to touchdown with a manual landing and it will retard as if doing an autoland.

[John H Watson]

My manuals say:

Autoland uses multi-channel autopilot for the final approach, flare and rollout. A single autopilot engaged allows approach operation through flare.

And another engineering manual says:

These conditions will cause an autopilot caution:

-Ground test mode
-Single channel flare mode
-...
-Pilot override if single channel engaged (servo detent trip)*

*25 degrees of wheel input

Could these manuals be any more ambiguous/contradictory

You need multiple channels engaged to control the rudder on approach, which is something ROLL OUT need otherwise to maintain a track the A/C will try to bank.

True. The rudder servos will not engage, so there will be no steering on the ground.

I also read this in one manual:

If single channel, these conditions cause the autopilot to disengage:
-Loss of autotrim valid 1&2
-Airplane on the ground (rad alt less than 5') during the flare mode

[emerydc8]

The confusing thing is we fly the -8 as well and on that beast, the A/T can be left on to touchdown with a manual landing and it will retard as if doing an autoland.

Of course, there isn't bupkis in the differences manual on this. I already checked.

-Single channel flare mode

Does not compute!

[Hardy Heinlin]

The flare function in this case might be a submode of the G/S mode, so that "G/S" remains annunciated instead of changing to "FLARE".

[John H Watson]

The 767 manuals also mention a single channel (A/P) flare:

e.g.

"A/P Caution light illuminates if single channel flare initiated. Disengagement automatically happens at 5' gear height".

"For single channel approach, the pilot would disengage the auto-pilot prior to flare. However, if disengagement is not initiated, flare would still take place. the A/P caution light illuminates at flare and disengagement automatically occurs at 5 feet gear height."

"NOTE: FLARE is normally a multichannel mode and therefore is not annunciated on the pitch FMA during a single channel approach."

Pin Program Option XYZ....  FD Bars are removed for single channel flare.
The full text for this option is:
• Full time flight director (P1B D3 to P1B K4) - flight director
commands are provided by any FCC anytime. F/D commands are
automatically removed from view for single channel flare.

[emerydc8]

I always thought that the minimum altitude for a single autopilot ILS is 100' AGL.
https://youtu.be/Se9cZx1zzNo?t=1h7m15s

[John H Watson]

I have the feeling he is talking about pilot operations rather than aircraft system operation.

[emerydc8]

Would this single channel flare mode be operative only while doing an ILS with only one A/P operating? Maybe it was an option for each airline.

[John H Watson]

I can't say I've come across any pin-programming notes for an option of this kind. It might explain why there is so many differing opinions on these subjects though 

I think we need a whole new message thread for that video link you posted. There were a lot of differences between PSX and his commentary due to airline options (and some plainly wrong stuff). Re the wrong stuff, the Instrument Source switches do affect systems, not just instrumentation.

[emerydc8]

Yes, United had some weird options like no F/D available on the side with the selected A/P.  That's why I asked if the single channel flare was an option. I wasn't aware that the source selector switches would affect anything other than what you would see. What system would be affected by the source select switches from a pilot's perspective?

This video has been so heavily used for type rating orals over the years that the designated examiner could sometimes tell if the examinee had used this to study. CF6 operators would ask their applicants when the EECs would go to the alternate mode. If reverse thrust was on the list, it was a giveaway.

[Hardy Heinlin]

I think we need a whole new message thread for that video link you posted.

Yes, a new thread please :-)

[John H Watson]

From the PPRuNe forum...

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.

Am I correct in assuming that "NGFMC" = New Generation FMC? i.e. the same one fitted to the 747-8? (With 100Mb of memory).

Might there be other differences between the NGFMC and the standard 747-400 FMC (e.g. regarding A/T behaviour?)