TOGA Between 50' & 400'

[Britjet]

Hoppie,
Unless I am wildly mistaken (sock-eating time?)...
The AT is in HOLD between 50ft and 400ft. Pressing TOGA in this height band will engage THR REF (with the FD system on), and the autothrottles will advance to GA thrust.

Peter

[emerydc8]

Peter,

I think you are right. My FCOM above is poorly-worded. It breaks up the phases as "On the Ground," "In flight (after takeoff until climb reference thrust limit active)," and "In flight (flaps out of up or glideslope captured)." I think the third phase is only referring to an approach situation where G/A is active. If this is true, then I think pressing TOGA on takeoff between 50' and 400' will select TOGA roll, remove the derates and activate the A/T in THR REF mode, so that maximum takeoff thrust is achieved.

I think the determining factor for what the A/T will set (THR or THR REF) if activated by a TOGA push  is not whether the F/D is on or off, but whether it is in takeoff mode (TO ref thrust displayed on EICAS) or G/A mode. I think the one-push/two-push feature only applies to the G/A mode. Thoughts?

Jon

[Hardy Heinlin]

I just tried a TOGA push in the big sim between 50ft and 400ft.
LNAV (green) and VNAV (armed) bith disappear and you just get THR TOGA TOGA.
HTH.

Peter.

[Britjet]

Hardy - the post following your quote was intended to mean that I got THR REF, when I said "sorry - yes", so it wasn't contradictory to what we are seeing in the FCOM.
To be fair - I wasn't checking for the thrust indication at that time - I was checking for LNAV being removed, and as I said I disconnected the autothrottle at the same time, so it whether it was THR or THR REF was effectively a logical guess.
As we are now talking about a different aspect, I'll try and test the various thrust indications when I am in the sim on Friday.
Peter.

[Hardy Heinlin]

I'm totally confused now, Peter. After the post following the above quote I asked you again to confirm your observation, and then you wrote again:

Absolutely Hardy - first push THR and second push THR REF.
Peter.

Only the latest forum comments from 4th and 5th January 2017 are contradictory. All was consistent in the discussion before ... :-)


|-|ardy

[Jeroen Hoppenbrouwers]

Video time ... with three phones  :-)

[Britjet]

Indeed! I am starting to lose the will to live here and it's probably all my fault LOL.
I think the apparent contradiction has arisen because we are assuming first push logic is that, in the GA mode, (which can happen at any time with flaps out of up) the system aims initially for 2000fpm which must presumably be THR? whereas if the system is in HOLD mode after take-off, we know from the FCOM that the FMA goes straight to THR REF.
I understand and share the confusion! There do appear to be separate things happening here though..
As Hoppie says - camera time. Watch this space for tomorrow's gripping instalment....
Peter.

[Hardy Heinlin]

Well, it makes sense if it goes straight to THR REF if, at the same time, it removes the derates. It's a fact that the first TO/GA push removes the derates. If the derates are removed, they are removed because max thrust is desired. And if max thrust is desired, THR REF is desired too. It makes no sense to open a bottle of beer if I don't want to drink it ...


Cheers,

|-|ardy

[Jeroen Hoppenbrouwers]

Add also that coming out of HOLD mode is a nice idea if you desire max thrust. For a while I assumed that because the system is in HOLD, it won't respond to an increase in reference thrust, but apparently pushing TOGA also ends HOLD mode (this is rather intuitive).


Hoppie

[Britjet]

Standby for the movie. In the meantime everyone try to keep calm and breathe deeply ;-)
Peter.

[emerydc8]

Hi Peter,

If you get a chance, can you press TOGA during the takeoff roll, while on the ground and above 100 knots? There is an interesting discussion over at pprune http://www.pprune.org/tech-log/588915-b777-toga.html#post9629062 regarding whether pushing TOGA on the ground above 100 knots will disarm LNAV and VNAV. I don't think it's this way on the 744, but it would be an easy check if you are in the sim. Thanks.
Jon

[Britjet]

I'll try to include it.

[Will]

Looking forward to the video. :-)

[torrence]

Way more exciting than waiting for the latest weekly Star Wars new episode XXXX  these days.
Cheers
Torrence

[Britjet]

Hi Peter,

If you get a chance, can you press TOGA during the takeoff roll, while on the ground and above 100 knots? There is an interesting discussion over at pprune http://www.pprune.org/tech-log/588915-b777-toga.html#post9629062 regarding whether pushing TOGA on the ground above 100 knots will disarm LNAV and VNAV. I don't think it's this way on the 744, but it would be an easy check if you are in the sim. Thanks.
Jon

Pushed it around 115 kts. No effect at all. No change to FMA or derate. LNAV and VNAV remained armed.
Peter

[Britjet]

Video as promised.
https://youtu.be/VwJj54lqJeM

I hope this answers some questions.
Peter

[emerydc8]

Thanks for checking, Peter. It is interesting that TOGA at 70' not only removes the active LNAV but also disarms the VNAV.

Jon

[Will]

Thanks, Peter!

[Hardy Heinlin]

Brilliant, Peter :-) Thank you!

All questions perfectly answered :-)


Cheers,

|-|ardy

[Hardy Heinlin]

For the first-push THR REF engagement I suggest to kinds of conditions:


THR REF engages or remains engaged on first TO/GA push when ...

(a) ... THR REF autothrottle mode or TO/GA pitch mode is already engaged

(b) ... thrust reference limit is a take-off limit (D-TO, TO, D-TO-..., TO-...)


I vote for (a). It's the simplest solution, and it's logical: If I am already in any TO/GA mode, I had already pushed the switch (before 50 kt, for example). Any further push will be a second push. A "first push" is only a first push when there is no TO/GA word on the FMA. In addition to this logic, a TO/GA push will never engage THR if THR REF is already engaged. That would be a power reduction.

(a) was also used in previous PSX versions.


|-|ardy