B777 EICAS 'flight controls' msg

[agg_karan]

In the QRH, it says for FLIGHT CONTROLS EICAS MSG...

1 Handling qualities are degraded. Pitch and roll control capability is reduced with fewer operating control surfaces.

2 Plan to land at the nearest suitable airport.

3 GND PROX FLAP OVRD switch . . . . . . . . . .OVRD

Note: Use flaps 20 and VREF 30 + 20 for landing. Higher approach speeds improve airplane maneuvering characteristics.


The question is,
Why is it that Boeing wants us to use FLAPS 30 VREF and add 20 knots and NOT use directly FLAPS 20 VREF?

Usually almost everywhere whenever we land with flaps 20 in a non-normal situation and QRH says use Flaps 20 VREF.

[Wizofoz]

You'll find Vref30+20 is slightly higher than Vref 20, and is used in some non-normals where control authority is an issue.

[No Fly Zone]

I think Wizofoz nailed it:ok:: improved control with degraded or possibly unknown control surface action. For most approaches/landings on a RWY that can reasonably accept your B777, the +20kt speed won't hurt you and it may help, perhaps when you most need it. (Brakes and tires cost a lot less than airframes etc.) Why the difference? Best guess (and only that) is that this is one of the few QRH issues where control may be seriously limited. Again, the +20K gives you more effective authority, perhaps when you most need it. I'm not a 777 driver, but when control becomes an issue, *slightly* higher speed usually helps, so land a little hot, stand on the brakes (4/MAX) and buy new tires later. (If pax aboard, you might also warn them. Not many have been through a MAX braking effort and it can be a shock if not prepared.)

[Pitch Up Authority]

The landing will be with Flaps 20 and Vref 30 + 20 selected in the FMC.
The app speed for F20 is for normal landing weights about the same as Vref 30 + 20. The difference is that all manoeuvring speeds are 20 kts higher to compensate for the loss of control.

Landing with F20 is also less demanding on the trim capacity.