A/T autodisconnection during manual flare

[emerydc8]

Thanks for verifying this, Peter.

Jon D.

[Hardy Heinlin]

I've sent Hardy a video of my latest Big Sim enterprise.
It was as I described earlier. (Although the landing may have been slightly more than 100fpm and as such is restricted viewing hem hem).
No FLARE or ROLLOUT annunciation, just SPD, LOC, GS.
No retardation of thrust levers, no IDLE annunciation
A/T disengage at about 5r ( difficult to tell as re-entry was rather rapid, but definitely less than 10ft)
SPD annunciation disappears, just blank remaining.
Thrust levers remained at approach setting throughout arrival and rollout.

Peter

Thank you, Peter.

(It may have been slightly more than 100 fpm because of a misconfiguration re Vref/flaps; the amber band was above Vref, hem :-) ...)

In this video ...

• The SPD mode blanks ca. 1.1 sec after 5 RA, or 0.1 sec after air-ground change. It's not clear which one is the trigger as it blanks after touchdown.

• The G/S mode blanks ca. 0.5 sec after the SPD mode has blanked. I guess the trigger here is the air-ground event.


Cheers,

|-|ardy

[Britjet]

Thanks Hardy...I was wondering if I had the right flap set! 800fpm - ouch!
Peter

[Hardy Heinlin]

飛行機運用規程
AIRPLANE OPERATIONS MANUAL 4.20.9
B747-8F
[...]
When autothrottle is used during manual landing, thrust reduces to IDLE at 25 feet
radio altitude when the pitch mode is VNAV SPD, VNAV PTH, V/S, or G/S. The
autothrottle does not retard if pitch mode is TO/GA or FLCH.

I got some feedback on a manual landing on the 744 with the legacy software (no NG). Sounds like IDLE does happen in the flare. So, where do we go with this?

-400F

Manual Landing
ATHR engaged.

At 25ft the mode changed from SPD to IDLE.

I delayed selecting reverse for a few seconds to see what would happen and the mode stayed in IDLE even after the nose-wheel touched down.

On selecting idle reverse the mode went BLANK the moment I moved the reversers from fully down.

The FCOM for the -400 (without NGFMC) is correct.

http://www.pprune.org/tech-log/577059-b744-autothrottle-manual-landing-4.html#post9345759

Summary:

• In the BA 744 sim there is no IDLE; the A/T mode just blanks upon touchdown. So the above feature must be airline specific.

• In the test in the BA sim the G/S mode was engaged. I assume the test results would have been the same if VNAV SPD, VNAV PTH, or V/S would've been engaged, i.e. the same modes that would engage IDLE at 25 RA in the new software.

• Aside from these modes, I guess the effect will also happen when no pitch mode is engaged. In short words: The effect will not happen when TO/GA or FLCH or ALT is engaged.

So this will be a new optional feature in PSX.


|-|ardy

[emerydc8]

Thanks Hardy.

[Hardy Heinlin]

I presume, in the new software, IDLE won't engage when the gear lever is not down and the flap lever is not in landing position. In cruise configuration there is no reason to idle the thrust when flying over an obstacle 25 ft below us.

And I presume that the new feature also works when an A/P is engaged. The reason why it works on a manual landing lies in my assumption that the FLARE mode (or autoland status) is no longer a requirement to enable the IDLE mode.

And I presume that the new feature will not work when the A/T is disconnected and armed, i.e. there will be no wake-up for the idle job.

And I presume that it will change from IDLE back to SPD when pulling up above 25 ft in V/S mode (if V/S was coupled with SPD before).

And I want it to be true that IDLE returns to SPD mode when pulling up above 25 ft in VNAV PTH (if VNAV was coupled with SPD before); similarly in this pull-up case, VNAV SPD will change the IDLE mode to THR REF mode.

[emerydc8]

And I presume that the new feature also works when an A/P is engaged. The reason why it works on a manual landing lies in my assumption that the FLARE mode (or autoland status) is no longer a requirement to enable the IDLE mode.

That sounds right. Really, it seems that the same A/T logic used in an autoland is just applied to a manual landing, or single-channel A/P landing; but, like you said, FLARE is not required to cause the A/T to go to IDLE.

In any case, I plan to use the "BA option" where it just goes to blank on touchdown.

Jon D.

[Hardy Heinlin]

This stuff is now implemented in 10.0.9-beta3:

http://aerowinx.com/board/index.php?topic=3685.0

[Will]

This is an old thread from 2016.

Any operators out there land with the autopilot off, but the A/T on, and see the "IDLE" happen during flare? Asking the same question a different way: does anyone use this feature?

I'm wondering if adding more 747-8 aircraft to the world's fleets has led more operators, perhaps, to use this feature on the 747-400 more often? I suspect you could make an argument for common operations across type, flying similar procedures on both aircraft.

Anyway, I'm curious to hear how many operators land the 747 with the A/T engaged.

[Hardy Heinlin]

I guess this is not a normal procedure but a safety feature in case the crew forgets to disengage it.
There was an incident with a crew landing with SPD | VNAV PTH and during the landing the A/T engaged THR REF, if I recall correctly.
And the crew was very surprised ...


|-|ardy

[Will]

Okay, that makes sense. Thanks.

[Owl]

According to Boeing it's intended to provide crew workload reduction and commonality with the 747-8 (and 777 also I suppose).

We have a small minority of aircraft in the fleet with this option but no-one ever makes use of it. Partly because you would have to be sure and double check the tail number to make sure you had it fitted each day.

Secondly its very existence is a strange contradiction because flying A/T with no A/P is something that Boeing specifically recommends in the FCTM that you shouldn't do...

Wouldn't look very good at the board of inquiry if something went wrong after you had ignored what they had said, even if it is just a recommendation, so why bother?

Owl

[Will]

I guess it's an extra layer of protection. If you screwed up and kept the A/T on (against Boeing's advice) it might be safer to have auto-IDLE instead of waiting precious seconds to realize your mistake and pull the throttles back.

That said, in thousands of hours and many landings in PSX, I've never forgotten to disengage the A/T when I've disengaged the autopilot. Maybe it's more of an issue if you alternate between types where you land with the A/T engaged. I don't know if that's a common practice on the 747-8.

[Captain_al]

No Will, it is not common practice to manually land with the A/T engaged in the -8 either. It is the same as the 400, not recommended in the FCTM. We do usually say if you are doing manual flying where the pitch is not changing much, you can leave the A/T on till a short final and then disconnect. A constant angle non-precision approach is an example of that. If you are maneuvering more and pitch is changing more while manually flying, then you want it off for obvious reasons of being out of phase between the pitch and thrust relationship, especially if you are not a smooth pilot. Leaving it on below 100 feet if you manually mis-judge the flare and start the flare maneuver sooner can result in power being added when you don't want it and float results, not very productive at that point...