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extricate
30th Dec 2016, 15:33
Hi there,

As soon as aircraft touches down, automatic GA will not be available, this is taken from FCTM. Where can I find more information as to why? Can't seem to find it in Fcom 2

ElitePilot
30th Dec 2016, 15:59
Have a look under System Description/Automatic Flight-Go Around. "TO/GA switches are inhibited when on the ground...". Very small paragraph but quite a big trap.

testpanel
30th Dec 2016, 16:13
And it's not only the B777, correct?

extricate
31st Dec 2016, 03:04
How do I define ground time? How many seconds after touchdown?

BuzzBox
31st Dec 2016, 03:44
extricate,

An automatic go around is not available any time after the aircraft touches down during landing, because the TOGA switches will be inhibited. If a go around is required after touch down, it must be performed manually, without flight director guidance. The TOGA switches become active again shortly after the aircraft becomes airborne again (2 seconds??). Thereafter, pressing the TOGA switches will restore the flight directors in TOGA mode.

I believe the reason for the inhibit is a certification requirement to prevent inadvertent activation of TOGA mode during a normal landing, which could cause a runway overrun if not handled correctly.

extricate
31st Dec 2016, 06:04
If you push throttle manually to full stop and went around after touching down and after liftoff, TOGA is pressed, does the system reduces the thrust to match 2000ft/min climb?

BuzzBox
31st Dec 2016, 06:33
No, it should give you THR REF. If you've already firewalled the thrust levers, then the thrust shouldn't change.

extricate
31st Dec 2016, 06:40
Thank you!

5LY
31st Dec 2016, 14:03
Another easy trap is a windshear at or near v1 on takeoff. If you decide to continue with max thrust you have to push the thrust leavers up manually. Pushing TOGA does nothing and you can easily waste a few seconds using up runway until you figure it out if you ever do.

JammedStab
31st Dec 2016, 14:29
In terms of thrust lever movement, this statement may be correct but(subject to confirmation), I believe that it is still important to press TOGA at this point in order to get the FD windshear recovery indications. So push and press.

flyhardmo
1st Jan 2017, 14:26
Pushing TOGA does nothing

It won't give you full thrust and I think that's what you meant. Above 80kts if you push TOGA it disarms LNAV and VNAV which is what Jammedstab maybe referring to.
After lift off pushing the TOGA switches will remove any derates or assumed temp.

JammedStab
2nd Jan 2017, 02:05
Can anybody explain why LNAV and VNAV are disarmed above 80 knots when TOGA is pushed. As far as I know, the 744 does not have this feature.

cf6-80c2b5f
2nd Jan 2017, 09:20
Hi JammedStab,

I think the 744 does have a somewhat similar feature in that if you push TOGA on takeoff between 50' and 400', LNAV will change back to TOGA roll mode. If you push TOGA above 400', both TOGA roll and TOGA pitch mode appear on the FMA.

Also, if you push TOGA after liftoff (with takeoff reference thrust displayed), and the A/T is still in HOLD (prior to 400'), it will remove any derates and activate the A/T in THR REF mode.

JammedStab
2nd Jan 2017, 14:08
Still different as far as I can tell. So, can anybody explain why LNAV and VNAV are disarmed above 80 knots when TOGA is pushed on the 777. As far as I know, the 744 does not have this feature.

cf6-80c2b5f
2nd Jan 2017, 18:18
I found this in the 777 FCOM 4.10.19. It seems to take the 744 logic a step further and will disarm LNAV and VNAV even on the ground, when above 80 knots. Maybe someone can explain the logic behind this. I'm thinking that for a windshear encounter during takeoff, you might not want LNAV or VNAV to go active?

Takeoff/Go-around (TO/GA) Switches
On the ground:
Push
below 50 knots and flaps out of up, activates autothrottle in THR REF mode at reference thrust limit selected on THRUST LIMIT page. If not pushed below 50 knots, autothrottle operation is inhibited until reaching 400 feet altitude
pushing either switch above 80 knots disarms LNAV and VNAV
In flight:
Push (after lift-off with takeoff reference thrust limit displayed)
removes takeoff and climb derates and assumed temperature thrust reduction
A/T in HOLD, activates A/T in THR REF mode
disarms LNAV and VNAV, if armed
between 50 feet and 400 feet, selects TO/GA roll mode
above 400 feet, selects TO/GA roll and pitch modes

flyhardmo
3rd Jan 2017, 02:00
I'm thinking that for a windshear encounter during takeoff,

I am not really sure why that is but I if I had to take a guess I would agree. Maybe also for engine failure scenario where you don't want to fly the LNAV track without having to reach up and fiddle with the MCP. I'm sure Tdracer will know the exact logic.

underfire
4th Jan 2017, 01:09
How do I define ground time? How many seconds after touchdown?

weight on wheels

underfire
4th Jan 2017, 01:31
Can anybody explain why LNAV and VNAV are disarmed above 80 knots when TOGA is pushed. As far as I know, the 744 does not have this feature.

For the 747..

on roll, with LNAV/VNAV armed, selecting TOGA, thrust moves to THR REF.
At 65kts, FMA reverts to HOLD and allows manual adjustment of thrust.
IF LNAV is armed, at 50', TOGA roll replaced with LNAV.
At 250' autopilot can be selected
If VNAV armed, at 400', TOGA is replaced with VNAV SPD

similar in the wording and intent.

JammedStab
4th Jan 2017, 03:45
So on the 744, if you push TOGA a second time, at 100 knots, will LNAV and VNAV be disarmed?

cf6-80c2b5f
6th Jan 2017, 18:20
Someone just checked this in the 744 sim. Pushed it around 115 kts. No effect at all. No change to FMA or derate. LNAV and VNAV remained armed.