B777 Flight Controls

Question 1

What are the three flight control modes?

Answer 1

Normal, Secondary, Direct

Question 2

When do the PFC’s do a self test in the normal mode? What indications occur when this happens?

Answer 2

After engine shutdown, During the test,
various EICAS alert and status messages display, trim indicator information blinks,
and various failure indications display on the flight controls synoptic.

Question 3

How do you know the PFC’s have finished their self test?

Answer 3

EICAS messages disappear, and the trim indicator and
synoptic display return to normal. This happens about two minutes after the EICAS caution message HYD PRESS SYS L+C+R is displayed.

Question 4

Which envelope protections are there and in what modes are they available in?

Answer 4

• stall protection
• overspeed protection
• bank angle protection

In the normal mode only

Question 5

What causes the flight controls to go into secondary mode?

Answer 5

When the PFCs can no longer support the normal mode due to internal faults or lack of required information from other airplane systems, they automatically revert to the secondary mode.

Question 6

What does it mean when you see FLIGHT CONTROL MODE?

Answer 6

Flight controls are in Secondary mode

Question 7

Which functions are not available in the secondary mode (7 items)

Answer 7

• autopilot • auto speedbrakes • envelope protection • gust suppression • thrust asymmetry compensation • yaw damping (may be degraded or inoperative). HNR, KPA - KQZ • tail strike protection

Question 8

What causes the PFC’s to go into direct mode? Can you manually seclect direct mode, if so how?

Answer 8

The ACEs automatically transition to the direct mode when they detect the failure of all three PFCs or lose communication with the PFCs. The direct mode can also be manually selected by moving the PRIMARY FLIGHT COMPUTERS DISCONNECT switch to DISC.

Question 9

Where do pilot inputs get send to in direct mode?

Answer 9

They bipass the PFC’s and are send direct to the ACE’s to move the flight controls

Question 10

In the direct mode, which functions are not available? 8 items

Answer 10

• autopilot • auto speedbrakes • envelope protection • gust suppression • thrust asymmetry compensation • yaw damping (may be degraded or inoperative) • manual rudder trim cancel switch, HNR, KPA - KQZ • tail strike protection

Question 11

How does the mechanical backup work if there is a total failure of all three flight control modes?

Answer 11

Cables from the flight deck to the stabilizer and selected spoilers allow the pilot to fly straight and level until the electrical system is restarted.

Question 12

After what AOB is backpressure required in the normal mode?

Answer 12

More than 30

Question 13

What do the PFC’s command in the landing flare while in manual flight?

Answer 13

PFCs command a slight nose down pitch command to provide the landing characteristics of other Boeing airplanes. The nose down command allows the pilot to apply normal aft column force during landing flare

Question 14

When are the primary pitch trim switches are inhibited?

Answer 14

When the autopilot is engaged

Question 15

How does the primary pitch trim operate differently in the air and ground?

Answer 15

On the ground, the stabilizer is directly positioned when the pilot uses the pitch trim switches. In flight, the pitch trim switches do not position the stabilizer directly, but make inputs to the PFCs to change the trim reference speed. The trim reference speed is the speed at which the airplane would eventually stabilize if there were no control column inputs.

Question 16

In the normal mode do you need to trim if you increase pitch or roll without activating envelope protection in you maintain the same airspeed?

Answer 16

No

Question 17

How is the alternate trim different from the primary pitch trim?

Answer 17

The Alternate trim levels move the trim reference airspeed (normal mode) and also move the stabilizer (all modes). The alternate pitch trim levers are linked to the stabilizer trim control modules (STCM) via control cables, and then mechanically to the stabilizer.

Question 18

What are some limitations using the alternate ptich trim levers in flight?

Answer 18

The alternate pitch trim levers should not be used with the autopilot engaged, or during stall or overspeed protection.

Question 19

How does stall protection work?

Answer 19

Stall protection limits the speed to which the airplane can be trimmed. The trim reference speed is limited by inhibiting trim in the nose up direction when the airplane slows to a speed where maneuver margin is limited. This trim inhibit speed is approximately the minimum maneuvering speed (top of the amber band) at lower altitudes, and can be 10 to 20 knots lower than the top of the amber band at higher altitudes. The pilot must apply continuous aft column pressure, at higher than normal force, to maintain airspeed below trim inhibit speed.

Question 20

How does overspeed protection work?

Answer 20

Overspeed protection limits the speed to which the airplane can be trimmed. At VMO/MMO, overspeed protection limits the trim reference speed so that trim is inhibited in the nose down direction. The pilot must apply continuous forward column force to maintain airspeed above VMO/MMO.

Question 21

What is ‘Elevator Variable Feel’?

Answer 21

The PFCs calculate feel commands based on airspeed. In general, control column forces increase: • as airspeed increases for a given column displacement, or • as column displacement increases.

Question 22

How is Secondary and Direct Mode Pitch Control different from Normal mode?

Answer 22

In direct/ secondary mode, the control columns now command a proportional elevator deflection instead of a maneuver command.

Question 23

How does the pitch control feel change in secondary/ direct mode?

Answer 23

In secondary and direct modes, the elevator variable feel system provides two feel force levels instead of a continuous variation with airspeed. The force levels change with flap position. With the flaps up, the feel forces provide maneuver force levels that discourage overcontrol in the pitch axis at high speeds. With flaps out of up, the feel forces decrease to provide force levels appropriate for approach and landing.

In the secondary and direct modes, both the primary pitch trim switches and the alternate pitch trim levers move the stabilizer directly. There is no trim reference speed.