TOGA Between 50' & 400'

[Britjet]

sorry - yes.  (i had a/t disengaged anyway to not make things difficult for my guest)
Peter.

[Hardy Heinlin]

So this is the full G/A logic with the first push setting THR for 2000 fpm (if not achieved already), and with the second push setting THR REF. So I need not make a special G/A submode for the take-off phase. Also, this disagrees with that quote from the manual which says below 400 ft only the roll mode will be replaced by TOGA.


|-|ardy

[emerydc8]

Hi Peter,

Thanks for checking this.

Jon

[Britjet]

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

[Hardy Heinlin]

Here's a design question. How would you guys design it?

Background:

• We know that the A/T mode is pitch mode dependent.
E.g. V/S sets SPD, FLCH sets THR, TO/GA sets THR and THR REF etc. In this context the roll mode is irrelevant.

• We know that the first push of the TO/GA switch sets THR, and the second push sets THR REF.

• We also know that any push of the TO/GA switch sets TO/GA roll and pitch modes.

• So we know that the TO/GA switch engages four modes: THR, THR REF, TO/GA roll, and TO/GA pitch.


Here's a go-around scenario, first flown with design A, then again with design B:


Design A:

1. On approach with blank FMA
2. Push TOGA; FMA indicates THR | TO/GA | TO/GA
3. Push LNAV; FMA indicates THR | LNAV | TO/GA
4. Push TOGA; FMA indicates THR REF | TO/GA | TO/GA


Design B:

1. On approach with blank FMA
2. Push TOGA; FMA indicates THR | TO/GA | TO/GA
3. Push LNAV; FMA indicates THR | LNAV | TO/GA
4. Push TOGA; FMA indicates THR REF | LNAV | TO/GA


The design question is: When the second push engages THR REF, should this also re-engage the TO/GA roll mode? Remember my notes above under "Background": The pilot wants more thrust. In this context the roll mode is irrelevant. So why should the second push re-engage the TO/GA roll mode? The design dilemma is that the TO/GA switch has four functions: It will not only engage A/T modes but also roll and pitch modes.


I don't think anybody knows how Boeing/Honeywell/Rockwell/Collins designed it.
Which design would you prefer? A or B?


Regards,

|-|ardy

[Britjet]

I would wish and expect A.
I think if the system tries to be too clever it gets more clever than the pilot, which is never a good thing. He should not have to second-guess the result. The famous exception to this is the THR switch, which no-one in their right mind touches at any time and which DOES make the wings fall off!
The answer lies, I think, in the expectation of the pilot. If the manual says it gives TOGA and removes LNAV, and this is the case, then the pilot's expectation is satisfied, and he can be assured of the result if pushing the TOGA button.
The windshear on approach case is also a determinative factor. Windshear recovery should be flown wings level, to optimize lift. Windshear recoveries are best flown with autopilot, so you don't want the aircraft suddenly making an LNAV turn in thus situation.
We tried this in the sim and LNAV is indeed removed whether it is first or second press.
Peter.

[Hardy Heinlin]

Very good.

In fact, design "A" will be in the next PSX update. It is required because otherwise it won't replace LNAV by TO/GA as long as the pitch mode is TO/GA (the pitch mode being in TO/GA is the only info for the logic to see that TO/GA roll mode engagement occured already; if this keeps inhibiting TO/GA roll re-engagement, LNAV will remain engaged, and that's what we don't like).


|-|ardy

[Jeroen Hoppenbrouwers]

I vote "A" as well, for another few reasons.

Who would push TOGA, reach up for the LNAV, and then after observing the aircraft not climbing as expected, reach back to the throttles and find TOGA and push it again?

I expect most pilots to just hit TOGA TOGA TOGA no matter what and forget about it. Certainly not coming back to it!

So design "A" and I may even add, include a timer that you need to double-push TOGA and not TOGA, get coffee, TOGA again.


Hoppie

[Hardy Heinlin]

In PSX update 10.1.1 any TO/GA re-engagement after 50 KIAS is now a GA mode which includes the entire go-around AFDS logic. In previous versions the TO/GA take-off phase only ended above 400 ft AGL.

http://aerowinx.com/board/index.php?topic=4020.0

(Refer to item 1.1.008.)


Regards,

|-|ardy

[emerydc8]

Thanks, Peter.

Just to be sure it's not a typo: You got "THR", not "THR REF"?


|-|ardy

Hi Hardy,

I'm not sure I ever understood whether this was a typo. Was Peter getting THR or THR REF when he pushed TOGA above 50'? The FCOM says that with the A/T in HOLD, it will activate the A/T in THR REF mode when pushed above 50'. In Beta 10.1.1, when I push TOGA above 50' (below 400'), it's going to THR --not THR REF. The derates are correctly taken out, and LNAV is replaced by TOGA roll, but the power stays at the original derate setting for takeoff and it stays in THR, even though TO is the reference N1. Is this what you wanted? Thanks.

Jon

[Hardy Heinlin]

Yes.

First push: THR -- which sets 2000 fpm minimum.

Second push: THR REF -- which sets thrust reference.


|-|ardy

[Britjet]

This is my FCOM...
'The TO/GA switches are inhibited when on the ground and enabled again when in the air for a go-around or touch and go.

With the first push of either TO/GA switch: • roll and pitch activate in TO/GA • autothrottle activates in thrust (THR) to establish a 2000 FPM climb • if current airspeed remains above the target speed for 5 seconds, the target airspeed is reset to current airspeed, (to a maximum of the IAS/MACH window speed plus 25 knots) With the second push of either TO/GA switch: • autothrottle activates in thrust reference (THR REF) at full go–around thrust"

Peter.

[Avi]

When do the TO/GA switches are enabled again on the ground (for "normal" takeoff) after they are inhibited due to landing?

Thanks,

[emerydc8]

This is my FCOM...
'The TO/GA switches are inhibited when on the ground and enabled again when in the air for a go-around or touch and go.

With the first push of either TO/GA switch: • roll and pitch activate in TO/GA • autothrottle activates in thrust (THR) to establish a 2000 FPM climb • if current airspeed remains above the target speed for 5 seconds, the target airspeed is reset to current airspeed, (to a maximum of the IAS/MACH window speed plus 25 knots) With the second push of either TO/GA switch: • autothrottle activates in thrust reference (THR REF) at full go–around thrust"

Peter.

Thanks, Peter. Is this THR the same if you wait until 400' before pressing TOGA? When I wait until 400', pressing TOGA in PSX results in THR REF. Of course, THR REF goes active at 400'. My FCOM above is a few years old. Maybe they've changed it since.

[John H Watson]

When [are] the TO/GA switches are enabled again on the ground (for "normal" takeoff) after they are inhibited due to landing?

http://aerowinx.com/board/index.php?topic=3548.0

Seems to be flaps out of up and below 50kts?...   After recent discussions on the FCU, possibly a flap position signal from the inboard LE flap position switches.

[Hardy Heinlin]

When I wait until 400', pressing TOGA in PSX results in THR REF.

If THR REF is already engaged (with VNAV SPD), TO/GA keeps it in THR REF mode.

If THR REF is not engaged (with FLCH, V/S or whatever), TO/GA first sets the THR mode.

[emerydc8]

Thanks, Hardy. I agree. I looked at my most current FCOM and it does clarify the original FCOM excerpt that I posted on the first page.

The original said, "(after liftoff with reference thrust limit displayed)." The FCOM below clarifies that it's "(after takeoff, until climb reference thrust limit active)." So once VNAV goes active, you would get THR REF if you pushed TOGA.

[Jeroen Hoppenbrouwers]

Hey -- "removes takeoff derates", that's a new one to me.

[Britjet]

Here is my FCOM on that phase..

After lift–off:
if a TO/GA switch is pushed with the takeoff reference thrust limit displayed
removes takeoff and climb derates and assumed temperature thrust reduction
A/T in HOLD, autothrottle annunciation is THR REF
between 50 feet and 400 feet, selects TO/GA roll mode
above 400 feet, selects TO/GA roll and pitch modes

So are we saying this?
between 50 and 400ft after take-off..
FD on - first push - THR REF, TOGA, TOGA and de-rates removed.
FD Off - first push - THR, TOGA, TOGA and de-rates removed.
?
I can check this out in the sim tomorrow..
Peter

[Jeroen Hoppenbrouwers]

Just to be complete: I guess that removing the derates is nearly invisible.

1. The annuciation is already THR REF. You change the reference thrust, but the indication remains the same. You should see the green numbers increase a tad.

2. The A/T is in HOLD mode, so it won't adjust upward when you remove the derates.


Hoppie