Idle Curiosity - B777 TOGA Switches

[C152_driver]

I guess it's not too hard to figure what prompted this question...

I've been reading that (in at least some) Boeing 777s the TOGA switches are inhibited by weight-on-wheels. Which leads me to wonder: why?

Can anyone explain to a very low-hours GA pilot what the benefit of disabling the switches once the aircraft has made contact with the ground is?

Thanks.

[ETOPS]

I have 5 years command on 777s and don't know the answer - it is a common design feature of most Boeing aircraft I have flown.

As it is "designed" into the system there must have been a conscious decision to make it so and the closest I can get is that initiating a go around after touchdown is extremely rare. It is also inadvisable in some circumstances (after reverse thrust selected for instance) such that special simulator training is given to cover just such situations.

Not wishing to pre-judge the EK accident I would think the lack of TOGA after landing might feature in the report - meet here in two years?

[C152_driver]

Thanks ETOPS, it will indeed be interesting to read what the enquiry finds.

[lederhosen]

The main reason is to avoid inadvertent pressing of the TOGA switch affecting rollout during an automatic landing. People do confuse switches as anyone who has seen someone press TOGA when meaning to disconnect the autothrottle on short finals will testify!

[Twiglet1]

Etops
The UPS crash in Dubai was Sept 2010 and the report came out July 2013.
Two years min I suspect old news is old news!

[Selfloading]

does hitting the TOGA switch have the same effect as pushing the thrust leavers all the way forward, in that you'd just have max thrust until the pilot made some sort of input?

[Wirbelsturm]

AFAIK the TOGA switches are inhibited on ground after landing to prevent mistakenly pressing one if you're fumbling for the reverse levers etc.

For the take off roll pressing the TOGA switch will give you the rated thrust selected during the performance figure calculations in the FMC. Once airborne pressing the TOGA switches once will give you HDG REF as a roll mode and TOGA for the thrust ref with an appropriate thrust to give you a climb rate of 2000fpm.

A second press of the TOGA switches will give you max rated available thrust.

Pushing the thrust levers fully forward will give you max available engine thrust.

[Selfloading]

Interesting, thanks.