B777 Secondary Mode V. A330 Alterante Laws 1 & 2

[Kimon]

What does B777's Secondary Mode equate in A330's Alternate Laws 1 & 2?
Does Secondary Mode = ALT 1 , ALT 1A, ALT2, ALT2A, ALT2B?
Or all the ALT Laws in one?

[Bpalmer]

The B777 in its "direct" mode attempts to do the same thing it does in its normal mode but with less data.
That is a g-load pitch with speed stability and roll direct .

The A330 Alternate 2 is a g-load pitch WITHOUT speed stability (indeed, the Airubs FBW does not use speed stability and thus requires no manual trimming), and roll direct.

On the A330, in roll direct the roll rate is increased to potentially 25°/sec (from the normal 15°/sec), even though there is some damping of the controls to limit the roll response.

The submode of 2A or B depend on the availability of angle of attack protection in each aircraft's situation.

So, there really is no point where the two are identical due to the design of the two control laws (speed stability , vs. g-load stability - which is pretty close to pitch stability)

[Kimon]

I thought that Airbus were vector-stable only and Boeing speed-stable only.
Or is it just the amount of bias because both speed and vector are needed so say Airbus is 80% vector and 20% speed and Boeing the opposite.
Understood that these stabilities whether speed or vector are part of flight-axis parameters that are heavily augmented but are they mutually-exclusive?
Can one mix speed-stability and vector-stability?

[A33Zab]

B777 Secondary mode:

The secondary mode cannot be manually selected.

The EICAS caution message FLIGHT CONTROL MODE is displayed.



... The following functions are not avaialble:

autopilot
auto speedbrakes
envelope protection
gust suppression
tail strike protection
thrust asymmetry compensation
Yaw damping (may be degraded or inoperative)
Elevator and rudder are more sensitive at some airspeeds.

The control column command a proportional elevator deflection instead of a maneuver command, there is no automatic pitch compensation for:


Thrust changes
Gear configuration changes
Flap and speedbrake configuration changes
Turbulence
Turns to 30 bank angle.
The elevator variable feel system provides two force levels instead of a continuous variation with airspeed.

Roll control is similar to roll control in normal mode.
Bank angle protection is not available
Spoilers 4,5 & 10,11 are locked out.

Yaw control is similar to normal mode, rudder response is slightly different, the rudder ratio changer is degraded to two fixed positions.

[Kimon]

Many thanks for your insight!
Are the following statements true on the B777 if it were an AF447?
1) Turning off the ADRs so as to force it in Secondary Mode à la A330 Alternate 1?
2) B777 is w/o aural SW only yokeshakers so it is not subject to the 60KNS / 30 KNS cut-out set-up?
3) B777's equivalent of THS AutoTrim is that trims for speed only not pitch.
Pitch authority is always driven via the elevators that command the stabs as opposed to the A330's separate - "divorced" - authority i.e. THS AutoTrim is separate entity that does not rely on elevator authority at all?

[A33Zab]

Cannot answer in detail, there is far more Airbus information available than Boeing.

AFAIK,

1// No, the OFF selection (ADIRU) is inhibited if airspeed > 30kts.
2// Yes IMO it is, AoA is compared to the AoA strip value, AoA is an ADIRU/SAARU output to WEU.
SAARU quits if airspeed < 50kts & ADIRU quits if airspeed < 30Kts.
3// IMO Auto trim only for configuration changes and bank angle compensation (in normal), PF needs to unload the elevator by manual pitch trim but I lack 777 in-depth system knowledge so I could be wrong.

A330 auto pitch trim will unload the elevators.

[Kimon]

Do you fly the A333ADV w/electrical rudder?

[A33Zab]

as SLF,
Once a year I 'fly' CAT 'D' simulator, in between those occassions my role is 'to keep them flying'. maintenance & engineering.
I'm familiar with both the mechanical as the enhanced (electrical) rudder.