B777 Flaps and Slats secondary and alternate mode

[felixthecat]

Just for my own clarification.

When the B777 reverts to secondary mode for the Flaps and Slats is it just in the electric mode for the item that has failed? i.e. Flaps primary fail would mean the flaps are now electric but the slats are still hydraulic? Also Slats primary fail would mean slats are now electric but flaps still hydraulic?

In the Alternate mode the flaps and slats are both electric no matter the failure bypassing the FSEU

[sleeve of wizard]

Sounds like you have a handle on things.:ok:

But don't take my word for it, a lot of good information can be found in the FCOM, give it a go next time.
This time I've done the work for you, "the flaps and slats can operate independently in either primary or secondary mode. However, independent flap and slat operation in the alternate mode is not possible."

[felixthecat]

That was how I read it....but for some reason in my head I had thought that it was either all hydraulic or all electric ....Here to learn :)

[JammedStab]

Sounds like you have a handle on things.:ok:

But don't take my word for it, a lot of good information can be found in the FCOM, give it a go next time.
This time I've done the work for you, "the flaps and slats can operate independently in either primary or secondary mode. However, independent flap and slat operation in the alternate mode is not possible."
Remember, when the operation is in secondary mode, it is a much slower movement. If one item operates slowly(electrically) while the others operate hydraulically(primary) you will get an asymmetry. Which of course will stop everything in secondary as there is still protection for this.

As stated in the book, " In secondary mode, flaps and slats are positioned by electric motors."

When the FCOM talks about flaps and slats operating independently, they are not talking about an individual flap or slat operating independently from their sister slats or flaps. They are talking about the slats operating independently from the flaps and vice versa. For example, in primary, when flaps 1 is selected, only the slats move(independent operation). As well, with flaps extended to 1 or greater in normal mode, autoslats operation happens at an approach to stall(they go from mid position to fully extended independent of the flaps. Flap load relief can happen in primary mode while slat load relief can happen in secondary mode. All independent movements from each other.

As stated earlier, there is no independent movement in Alternate.

[sleeve of wizard]

Jammedstab,

Your statement about asymmetry is incorrect.
If you have a Slat Primary Fail, only the Slats have reverted back to secondary, the flaps will still operate in the Primary mode. Look at the Slats Primary Fail Checklist, Note: Plan more time for slower slat operation. No mention of slower flap operation!
Flaps Primary Fail checklist also has a note: Plan more time for slower flap operation.
The asymmetry is sensed by the Left Inboard, Left Outboard, Right Inboard and Right Outboard sensors of the respective system, this detects the asymmetry between the left and right flaps or slats, not as you say an asymmetry between the flaps and slats. :ok:

[Wizofoz]

sleeve of wizard is correct.

Somewhat moot, as the most likely cause of flap or slat primary fail is loss of the center hydraulic system, in which case you end up in secondary for both, BUT should there be a failure of ONLY hydraulic activation of either slats or flaps, the other surface stays in primary mode.

[JammedStab]

It looks like I misread the initial question. I thought there was discussion about one of the slats or one of the flap sections operating electrically while the rest of the slats operated hydraulically or the rest of the flap sections still operated hydraulically.

[felixthecat]

No I realise that if Flaps are in Secondary, then ALL of the flaps are then driven electrically. Equally if Slats are in Secondary, then ALL of the slats are then driven electrically. My question was if the flaps were in secondary and electric would the slats also be so and vice versa.

Thats all been cleared up now :) Thanks

[TwinJock]

Can anyone explain to me what use this information is to me on a daily basis, or even during a non-normal involving flaps / slats?

Don't sweat the small stuff Felix - you REALLY do not have to know this information mate....

[Calmcavok]

It may help you when planning your approach in such a non-normal situation? For example the slowest flap/slat setting to deploy is from UP to 1, which is mid-range slat only, so even slower deployment in secondary. Therefore you could be confident that in slat secondary mode if the slats only were electrically actuated but the flaps remained hydraulic, 5-20 would come out at the normal rate and then 20-25/30 would be slower. Just my $0.02...

[Wizofoz]

I despair- a pilot who doesn't think it's worth knowing how his aircraft works.