B777 FLAPS DRIVE

[Buckshot16]

The FLAPS DRIVE checklist directs the flight crew to :

Flaps position 5 or less :

Note: Move the FLAP lever to 1 and use VREF 30 + 40 for landing. This ensures the slats are extended.

Now, the scenario :

If the system was operating correctly in PRIMARY MODE when FLAPS 1 was selected, then the LE SLATS would extend to the MID-RANGE ( SEALED position ), then when you select FLAPS 5 the trailing edge flaps move from their up position to the 5 unit position, but during their motion the EICAS "FLAPS PRIMARY FAIL" appears, then immediately followed by "FLAPS DRIVE".

So why would you move the FLAP LEVER to the FLAPS 1 detent ?
The leading edge slats are already in the "extended" mid-range ( Sealed position ).

The last sentence of the note confuses me.:confused:

Just a note, remember the PRIMARY MODE of flap sequence for EXT is SLATS move then FLAPS and vice-versa for RET.

Looking forward to what is probably a simple answer that I can't see.:ugh:

[Roj approved]

I'm guessing the 777 and the 787 have a similar system, as we are all now rated on both

On the 787 below 225kts and with a high angle of attack you will get Autogap, ie: slats will fully extend.

So the Vref 30+40 will keep you below 225kts, and allow the Autogap function to work.

Why move the flap selector back to 1?

In the section about UNCOMMANDED FLAP OR SLAT MOTION -it states the conditions that have occurred to get the EICAS messages "Flaps Primary Fail" then "Flaps Drive".

Move away from commanded position

Continue to move once reaching command position

Move in opposite direction to commanded

So leaving the lever in 5 may allow the flaps to move, (highly unlikely as it also says the system will go to secondary mode and shutdown if there is any further movement)

but if the lever is in 1, there is no danger of movement as you haven't asked anything of the flap system.

Just my take on it

[Long Haul]

That's right, once you're committed to a flaps 1 landing, you don't want them moving to 5 when you least expect it.

[JammedStab]

Something still doesn't make sense. If the flaps were at 5 and 20 was selected but they did not move, then using the above reply, we wouldn't want them to suddenly move to flaps 20 once you are comitted to a flaps 5 landing. So why is the selector not moved to flaps 5 from 20.

I think that there is another reason.

[Roj approved]

Look at the NNC procedure, it's got a provision to cover that.

Flap between 5 and 20, use current flap.

So if the flaps were at 5, and failed when you selected 20, match the lever to the flap position, ie: 5, and there can be no movements as there is nothing selected.

[sleeve of wizard]

Buckshot, you are considering that the failure occurs during extension. What about during retraction?
Scenario - flaps are retracting on schedule and you get the EICAS message after you have selected flaps up. The Flaps Drive checklist must cater for all scenarios.