Flight Controls
Boeing 787 / 777 Flight Control Summary – ATA 27
ACE’s (Actuator Control Electronics)
The Number of ACEs Are 4 (L-C1-C2-R), The System Is Designed So That A Single ACE Does Not Control All Surfaces In Any Axis, To Improve Reliability
PFC’s (Primary Flight Controls)
The Number Of PFC’s Are 3 They Provide A High Level Of Computing That Enhance flight Control Operation And flight Envelope Protection In Normal Mode
Pilot Trim Inputs Are Minimized Due To The PFCs Automatically Controlling Pitch In Response To Flaps/Speedbrake, Gear Configuration, Thrust Changes, And Up To 30° Of Bank.
The PFCs, Decrease Elevator Deflection, To Reduce The Potential Of A Tail Strike If Detected* The PFCs Provide Enhance Crew Awareness Of Approach To Stall Protection, It Limits The Speed To The Minimum Manoeuvring Speed. (Top Of The Amber Band)
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Primary Flight Controls Mode’s
Normal Mode
It Provides The Highest Level Of Enhanced Flight Control
The Autopilot Is Available In Normal Mode
Other Features provided Such As:
- Gust Suppression
- Automatic Speed Brake
- Yaw Damping
- Flight Envelope protection (Tail Strike Protection, Bank Angle Protection, Overspeed Protection, Stall Protection)
- Roll/Yaw Asymmetry
- Cruise Flaps
- Autodrag
Secondary Mode
(ACEs To PFCs To ACEs To Actuators), The Actuators Are Either Hydraulically OR Electrically Powered.
Autopilot And Flight Envelop Are Not Available.
The PFCs Automatically Revert To The Secondary Mode, When Unable To Maintain The Normal Mode. (Lack Of Required Information Such As Inertial Data, OR Flap/Slat Position), If The Condition That Caused The Degradation Is Temporary, The System Will Automatically Upgrade To The Normal Mode. (Manual Selection To Secondary Mode Is Not Possible)
All Flight Surfaces Remain Operable. Yaw Damping Is Degraded.
An Additional Feature, Wheel To Rudder Cross-Tie, Is Available And Reduces Sideslip And Vertical Fin Loads.
If All 3 PFCs Fail OR Communication To The PFCs Fail, The System Can Automatically Revert To Direct Mode.
Direct Mode
(ACEs to Accumulators)
Autopilot And Flight Envelop Are Not Available
The Direct Mode Can Be Manually Selected, By Moving The PRIMARY FLIGHT COMPUTERS Disconnect Switch To DISC. If The Switch Is Returned To The Auto Position And The PFCs Are Operative, Automatically will Revert To The Highest Available Mode (Normal OR Secondary).
An Additional Feature, Wheel To Rudder Cross-Tie, Is Available And Reduces Sideslip And Vertical Fin Loads
EICAS Message FLIGHT CONTROLS, Displayed If Multiple ACEs And/ OR Hydraulic System Failures, That Cause The Loss Of Significant Number Of Control Surfaces OR Other Control System Faults Are Detected
High Lift Devises
Flaps
Two Single Slotted Flaps1 Inboard And 1 Outboard
- 10 Flap lever positions UP-1-5-10-15-17-18-20-25-30
- Actual Movement Of The Flaps 5-10-15-17-18-20-30
- Take-Off Flaps 5-10-15-17-18-20 Landing Flaps In Normal Conditions 25 or 30
Cruise Flaps
TEVC, Trailing Edge Variable Camber, They Are An Automated Function That Optimizes Performance In Cruise By Varying The Camber Of The Wing To Reduce Drag, And Reduces Fuel consumption, Operates Only Above 25,000 feet, And Between .54 to .87 Mach In Normal flight Control Mode (Flaps, Ailerons, Flaperons And Spoilers Are Used As Cruise Flaps)
Krueger flap
1 On Each Wing
Provides a seal between the inboard slat and the engine nacelle to increase lift. They have 2 PositionsRetracted OR Deployed
Flaperon
1 On Each Wing Operated By 2 Actuators
Flaperons Are Always Active Regardless Of Speed During Flight, However During Takeoff, They Are Hydraulically Pressurized At 85 to 100 knots.They Are Used As Cruise flaps, Above 25,000 Feet And A Speed Between .54 to .87 And In The Vertical Gust Suppression feature
Slats
1 Inboard & 5 Outboard
Slat positions: (Retracted)- (Middle)- (fully Extended)
Actual Movement Of The Slats, Flap Lever Positions 1-25
Spoilers
Total 14-(7 On Each Wing). 4 Outboard & 3 Inboard Of The Flaperons 1 Actuator To Each Spoiler
Used As Speed Brakes And To Assist In Roll Control, Spoilers On Opposite Wings Are Symmetrically Paired.
Speedbrakes Automatically Extend When, The Landing Gear Is Fully On The Ground & Thrust Levers Not In Takeoff Range.
Used In The Auto Drag Function By, Raising The Most Outboard Spoilers During Approach.
The Spoilers Automatically Move Up Slightly During Engine Start And Taxi To Prevent Contact With Moving Flaps.*The Spoilers Drooping Decreases The Gap Between The Trailing Edge Of The Spoilers And The Upper Surface Of The Flaps
Aileron
1 On Each WingEach Aileron Is Operated By 2 Actuators
Has An Auto Drag Function Operates By Deflecting The Ailerons Upward And Raising The Most Outboard Spoilers, While Maintaining Airspeed To Assist In Glideslope/Glidepath Capture. Functions Only When In Landing Config, Flaps 25 OR 30 And Thrust Levers At Idle. This Function Is Gradually Removed Below 500 Feet, Also Used In The Vertical Gust Suppression feature. The Ailerons Droop Symmetrically To Improve Slow Speed Performance, When Drooped The Ailerons Provide Roll Control, And The Flaperons When Drooped Still Provide Roll Control.
Elevators
Powered By 2 Actuators, Each Powered By A Different Hydraulic System.
Right side (R/ Hyd sys– C/Hyd sys)Left side (L/ Hyd sys- C/Hyd sys)
Each Elevator is Hinged On The Rear Spear Of The Horizontal Stabilizer. Also Used In The Vertica Gust Suppression feature
Provides Conventional Short-Term Pitch Control Until The PFCs Automatically Trim The Horizontal Stabilizer To Neutralize The Elevator Loads.
Horizontal Stabilizer
Provides pitch control
Powered By 2 Independent Electronic Motors, With 2 Brakes Per Motor, (1 Electronic And 1 Mechanical), It Is Positioned Using Two Different Channels.The Channels Are Powered By the L2 And R2 AC buses.
Column Cutout Is Designed To Stop The Effects Of An Uncommanded Pitch Trim Input From Jammed OR A Failed Pitch Trim Switches. If A Nose Up OR Nose Down Opposed By Either Control Column For More Than 2 Seconds, The Column Cutout Function Disables The Pitch Trim Switch Commands Until Input Indicates No Trim Input. If Cutout Function Remains Active For More Than 20 Seconds, The Uncommanded Input Is Removed By System Shut Down. Only Available In Normal And Secondary Modes.
Rudder
One Single Rudder
Becomes Active At 60 knots During Takeoff. A Rudder Ratio Changer Automatically Reduces Rudder Deflection As Airspeed Increases. Sufficient Rudder Authority Is Maintained In Cross Winds And Single Engine Operation.Rudder Features, Yaw Damping, Lateral Gust Suppression And Asymmetry Compensation.
- The Ailerons, Flaperons And Spoilers Move Down When Flaps Extend Past Flaps 1
- Bank Angle Protection Is Active When The Bank Angle Exceeds 35°, The Airplane Will Bank Back To 30°
- A Separate Sensing System Is Used To Alert The Crew If The Aircraft CG Is Different From The Values Entered In The FMC, 2Pressure Transducers On The Nose Gear Measure The Actual Gross Weight. If A Disagreement Will Result In An EICAS Advisory Message GREENBAND.
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Modes Of The Flap And Slats Computers
Primary
Flaps And Slats Are Computer Controlled Based On Flap Lever Position And Are Powered By The Centre Hydraulic System.
The Flap/Slat System Is Equipped With Autoslats, Load Relief, And Skew/Asymmetry Protection
The Meaning Of Asymmetrical, Symmetrical Means Both Sides Of Something Are Identical, Asymmetric Means The opposite.
Flap/Slat Extension Inhibit Protection Against Deployment During Cruise | IF Speed Greater Than 260 KTS OR Altitude Above 20,000 |
Autogap Only Available When The Flap lever Is In Flaps 1-5-10-15-17-18-20 positions. (Only When Slats In The Middle Position And Airspeed Is Below 240 KTS | At High Angles Of Attack Extends Slats Automatically From Middle Position To The Fully Extended Position. This Increases Wing Camber, Lift, And The Margin To Stall. They Return Again To The Middle Position After AOA Decreases. |
3–Flap Load Relief If Flap Airspeed Placard Limits Exceeded With Flaps In 15 Through 30, LOAD RELIEF Is Displayed. It Protects The Flaps From Excessive Air Loads | Flaps will Automatically Retract To An Appropriate Position To Airspeed, when Airspeed is Reduced the Flaps Automatically Re-Extend As Airspeed Allows And Only To The Maximum Flap Position Commanded |
Asymmetry/Skew Detection EICAS Message FLAPS DRIVE or SLATS DRIVE | The Flap and Slat Systems Automatically Shut down when Skew Condition OR Asymmetric Deployment Is Detected. |
Uncommanded Motion Detection EICAS Message FLAPS OR SLATS PRIMARY FAIL If Motion Continues, The System Will Shut Down, With An EICAS Message FLAPS OR SLATS DRIVE. | Is Detected when the Slats OR Flaps Move Away From The Commanded Position OR Continue To Move After Reaching A Commanded Position OR Move In A Direction Opposite To The Command Position. |
Flap OR Slat Disagree Detection EICAS Messages FLAPS or SLATS DRIVE In The Primary Mode, Will Cause An Automatic Transfer To Secondary Mode, With An EICAS Caution FLAPS PRIMARY FAIL or SLATS PRIMARY FAIL, if the Motion Continues, The System Will Shutdown, With An EICAS Caution FLAP DRIVE or SLAT DRIVE | If Flaps OR Slats Do Not Move When Commanded OR They Move Too Slowly. |
Secondary Mode
A Degradation Of The Normal System
An Automatic Switch To Secondary Mode Occurs In Case Of
- The Centre Hydraulic System Fails
- The Primary Mode Fails To Move The Flaps OR Slats To The Selected Position
- The Flaps OR Slats Primary Control Fails
Note: In Secondary Mode The Flaps And Slats Are Still Computer Controlled Based On flap Lever Position, But May Be Powered Either Hydraulically, OR Electrically. If The Rate Of Control Surface Movement Decreases Significantly The Operation Switches To The Electric Motors. Because The Flap And Slats Are Separate Systems, One System Could Be Operating In The Secondary Mode, While The Other System Operating In The Primary Mode.
The Position Of The Flaps And Slats Are Shown Independently, The Display Is Divided Into LEFT And RIGHT. The Line And Number Are Magenta while the Flaps And Slats Are In Transit; And Turn Green When They Reach The Commanded Position
Sequencing Of FLAPS/SLATS In The Secondary Mode
| SLATS | Flaps 1 Commands The SLATS To Move To The Fully Extended Position. |
| FLAPS | FLAPS 5, 10, 15, 17, 18 and 20, Commands The FLAPS To Move To The Selected Position. (In The Secondary Mode Flap Operation Is Limited To Flaps 20) |
Automatic Protection Features In Secondary Mode
| Flap/Slat Extension Inhibit Protection Against Deployment During Cruise | IF Speed Greater Than 260 KTS OR Altitude Above 20,000 |
| Pregap Only Available When The Flap lever Is In Flaps 1-5-10-15-17-18-20 positions. (Only When Slats In The Middle Position And Airspeed Is Below 240 KTS | The Movement Of The Slats Are Too Slow To Respond To The Autogap Function, From The Middle Position To The Fully Extended Position To Compensate The Slats Are Pre-Positioned To The fully Extended Position. |
| 3–Slat Load Relief The Airspeed Limit For The Fully Extended Slats Position Is 240 knots. In Primary Mode The Highest Airspeed Exposure With Fully Extended Slats Is To The Flap Load Limit Speed (180 knots) for flaps 25. If Slats Are Fully Extended And Speed Becomes Greater Than 240 knots They Will Retract To The Middle Position And The LOAD LIMIT Displays | (if Flap’s 1 Is Selected Just Below It’s limits 260 KTS In The Primary Mode, And A Failure Occurred Resulting In The Switching To Secondary Mode, The Pregap Function Will Attempt To Fully Extend The Slats To The Fully Extended Position, Resulting In An Overspeed Exceedance, This Is Why Slat Load Relief Is Required Only In The Secondary Mode) |
| Asymmetry/Skew Detection EICAS Message FLAPS DRIVE or SLATS DRIVE | The Flap and Slat systems Automatically Shut down when Skew Condition OR Asymmetric Deployment Is Detected. |
| Uncommanded Motion Detection EICAS Message FLAPS OR SLATS PRIMARY FAIL If Motion Continues, The System Will Shut Down, With An EICAS Message FLAPS OR SLATS DRIVE. | Is Detected when the Slats OR Flaps Move Away From The Commanded Position OR Continue To Move After Reaching A Commanded Position OR Move In A Direction Opposite To The Command Position. |
| Flap or Slat Disagree Detection EICAS Messages FLAPS or SLATS DRIVE In The Primary Mode, Will Cause An Automatic Transfer To Secondary Mode, With An EICAS Caution FLAPS PRIMARY FAIL or SLATS PRIMARY FAIL, if the Motion Continues, The System Will Shutdown, With An EICAS Caution FLAP DRIVE or SLAT DRIVE | If Flaps or Slats do not move when commanded or they move too slowly. |
Alternate Mode
There Is No Automatic Switching To Alternate Mode.
There Are No Automatic Protection Features
When Directed By The Non-Normal Procedure, The Alternate Mode Must Be Manually Selected By The Crew.
Alternate Mode Is Selected By Pressing The ALTN FLAPS ARM Switch On The Control Stand. In Alternate Mode Flaps And Slats Are Electrically powered And Directly Controlled By The Flight Crew Using The ALTN FLAPS RET/EXT Switch. (Flap Lever Is Disabled)
Slats Will Only Be Extended To The Middle Position And The Flaps to 20.
In Alternate Mode Flaps And Slats Are Electrically Powered And Directly Controlled By The Flight Crew Using The ALTN FLAPS RET/EXT Switch. (Flap Lever Is Disabled)
Slats Will Only Be Extended To The Middle Position And The Flaps To 20.