Flight Controls & Flight Control Laws

Question 1

What type of flight control system does the A320 family aircraft utilize?

Answer 1

• Fly-By-Wire system

Question 2

Describe how the flight controls are controlled and activated.

Answer 2

• Electrically Controlled and Hydraulically Activated

Question 3

How is NORMAL LAW indicated on the PFD?

Answer 3

• Green “=” for pitch, bank, and over speed limits

* Amber/black (ALPHA PROT) airspeed tape

Question 4

How is ALTERNATE LAW indicated on the PFD?

Answer 4

• Amber Xs (indicating lack of NORMAL LAW protections)

Question 5

How is DIRECT LAW indicated on the PFD?

Answer 5

• Amber “USE MANUAL PITCH TRIM”

* Amber Xs (indicating lack of NORMAL LAW protections)

Question 6

How is MECHANICAL BACKUP indicated on the PFD?

Answer 6

• Red “MAN PITCH TRIM ONLY”

* Amber Xs (indicating lack of NORMAL LAW protections)

Question 7

When operating in NORMAL LAW in “flight” mode, what does the side stick command for pitch and roll?

Answer 7

• Pitch – G load

* Bank – Roll rate

Question 8

What is the significance of the Side Stick Priority (Red Arrow) Light?

Answer 8

• The other pilot has gained side stick authority

Question 9

Name the Flight Control Computers and the number of each.

Answer 9

• ELAC – Elevator Aileron Computer (2)
• SEC – Spoiler Elevator Computer (3)
• FAC – Flight Augmentation Computer (2)

Question 10

What are the some of the ELAC functions?

Answer 10

• Normal elevator
• Normal aileron
• Normal pitch and roll
• Alternate pitch
• Direct pitch and roll
• Abnormal alt
• Aileron droop
• Autopilot orders

Question 11

What are some of the SEC functions?

Answer 11

• Normal roll
• Speed brakes
• Alternate pitch
• Direct pitch
• Direct roll
• Abnormal altitude

Question 12

What does SEC 3 control?

Answer 12

• Spoiler Control – one flight spoiler and one ground spoiler on each wing

Question 13

What are some of the FAC functions?

Answer 13

• Rudder Trim
• Rudder travel limit
• Yaw control
• Flight Envelope Protection – vertical
• Windshear Protection
• Low Energy Warning Protection
• Alpha Floor Protection
• PFD speed scale

Question 14

What should happen to the THS after landing?

Answer 14

• Reset to zero

Question 15

Describe some of protections a pilot will have in NORMAL LAW.

Answer 15

• High Speed
• High Angle of Attack (AOA Alpha Protection)
• Load Factor Limitation (+2.5G / -1.0G)
• Pitch Attitude (30° UP/15° DN)
• Bank Angle (67°)

Question 16

Describe High Speed Protection.

Answer 16

• If VMO/MMO plus a predetermined factor is exceeded, the system induces a pitch-up input to limit aircraft speed.

Question 17

What, if anything, can a pilot do to override high-speed protection pitch up?

Answer 17

• It is not possible to override a protection while still in NORMAL LAW. In this case the aircraft would need to be forced into ALTERNATE LAW (by turning 2 ADRs off, for example)

Question 18

What is ALPHA MAX?

Answer 18

• The maximum angle of attack allowed in NORMAL LAW, indicated by the top of the red strip on the airspeed scale.

Question 19

How does High Angle of Attack Protection operate?

Answer 19

• When the angle of attack exceeds ALPHA PROT, pitch trim ceases and angle of attack is now proportional to side stick deflection, not to exceed ALPHA MAX even with full aft side stick deflection.

Question 20

What protections, if any, does a pilot have in ALTERNATE LAW?

Answer 20

• Load Factor
• High-speed stability
• Low speed stability

Question 21

What protections, if any, does a pilot have in DIRECT LAW?

Answer 21

• None

Question 22

When, if at all, does flare mode activate in ALTERNATE LAW? Describe the whole process.

Answer 22

• There is no flare mode if operating in ALTERNATE LAW. The aircraft proceeds directly from ALTERNATE LAW to DIRECT LAW when the gear is selected down, and flare mode will not be available.

Question 23

If in ALTERNATE LAW, when will the aircraft revert to DIRECT LAW?

Answer 23

• If the controls degrade to ALTERNATE LAW for any reason other than recovery from abnormal attitude, DIRECT LAW automatically becomes active with gear extension and autopilots not engaged. In this case, full use of autopilot is recommended until they must be disconnected.

Question 24

When is there a direct relationship between side stick and flight control surface deflection?

Answer 24

• When in DIRECT LAW

* When below 100 feet

Question 25

It’s common Airbus philosophy that the Airbus cannot stall in NORMAL LAW. However, there are conditions in which it can. Describe how this can happen.

Answer 25

• Faulty Radio Altimeter
• A good pilot will operate under the philosophy that anything can happen.
Preventative systems such as (ALPHA PROT, ALPHA MAX, etc.) could interpret bad data as valid data and subsequently fail to recognize the actual angle of attack or flight path of the airplane. Therefore, it is hard to point to exact scenarios when the Airbus can stall in NORMAL LAW. We need to understand anything is possible and we should recognize stall indications and recover regardless of the active control law.

Question 26

After recovery from an unusual attitude, what control law would the aircraft likely be in?

Answer 26

• ABNORMAL ATTITUDE LAW

Question 27

How would the aircraft enter ABNORMAL ATTITUDE LAW?

Answer 27

• By exceeding approximately double the NORMAL LAW limits.

Question 28

What is the purpose of ABNORMAL ATTITUDE LAW?

Answer 28

• Allows the aircraft to be recovered from an unusual attitude.

Question 29

If the flight crew is flying at 300 knots and they happen to pull full back on the side stick, how high can they pitch up?

Answer 29

• 30°up

Question 30

If the flight crew selected 100 knots on the speed knob, how slow would the
aircraft fly?

Answer 30

• VLS

Question 31

Describe, in detail, what would happen if the flight crew slowly pulled the thrust levers to idle.

Answer 31

• As airspeed decays, the THS adjusts the pitch attitude to maintain altitude.
• If the angle of attack increases to a threshold value, known as ALPHA
PROT, the pitch function of the side stick changes. Stick movement commands a specific angle of attack instead of a G load change.
• Since auto trimming is inoperative, the pilot must hold continuous back pressure in order to fly slower than the speed for ALPHA PROT.
• The side stick no longer provides a “G demand.” Instead, the pilot is requesting a specific angle of attack with the side stick.

Question 32

Continuing the scenario above, describe what would happen if the flight crew continued to pull back on the side stick. How slow would the aircraft go?

Answer 32

• The speed corresponding to ALPHA MAX
• With the stick full aft, the elevators will adjust the pitch attitude to maintain a
maximum safe angle of attack (ALPHA MAX). This maximum angle of attack, induced by the pilot, is slightly lower than the stall angle of attack; therefore, the aircraft theoretically cannot be stalled in NORMAL LAW.

Question 33

At some point during this demonstration the AUTOTHRUST automatically applies TOGA power. What is this protection, and how does it work?

Answer 33

• ALPHA FLOOR is a function of AUTOTHRUST. It will activate at any airspeed based on angle of attack and automatically apply TOGA thrust regardless of thrust lever position.
• ALPHA FLOOR is available if the AUTOTHRUST is functional (it does not need to be active), an engine is running (not both), and the aircraft is in NORMAL LAW.
• Angle of attack protection does not depend on ALPHA FLOOR to function.

Question 34

Describe what would happen if a flight crew attempted to overstress the aircraft while in NORMAL LAW.

Answer 34

• Maneuver protection prevents a pilot from over stressing the aircraft by limiting flight control inputs.
• If G loads become greater than normal, they are displayed in amber on the lower ECAM above the digital clock.
• When the side stick is pushed forward, less than 1G is commanded. A given pitch input always results in the same pitch response regardless of airspeed.
• When the stick is returned to neutral, the new pitch is held constant regardless of airspeed changes.

Question 35

What will happen if the pilot over speeds the aircraft? Are there any protections that are available to the flight crew?

Answer 35

• An over speed causes the flight control computers to provide a nose up input to reduce aircraft damage due to excess speed. This protection limits the maximum airspeed by increasing the pitch attitude even if full forward stick is held.
• The speed at which this protection activates is shown on the airspeed indicator as a green “=” sign.
• An over speed warning is generated as VMO is exceeded (specifically at VMO+4). This warning can only be silenced by the EMER CANCEL pushbutton.
• If the stick is released, the speed will return to VMO/MMO. The protection will allow a momentary increase in airspeed to permit any necessary maneuvering but then the speed will again slow to the limit.
• If high-speed protection is active, bank angle is limited to 45°. Bank angle is also limited to 45° if angle of attack protection is active, in either case the limit marks do not move.
• If high-speed protection is active, positive spiral stability occurs at all bank
angles, and control pressure is required to hold any bank angle greater than
zero.
• It is possible to over speed the aircraft. The computers merely limit the maximum attainable speed.

Question 36

When a pilot rolls into a bank, what is provided by the Flight Control Laws?

Answer 36

• In “flight” mode of NORMAL LAW, roll control is a roll rate demand. Side stick inputs commands the ailerons, spoilers 2-5, and the rudder to achieve the commanded roll rate with bank angle protection, turn coordination, and Dutch roll damping.
• The roll rate demanded by the pilot is proportional to side stick deflection. When the side stick is neutral, the ailerons and spoilers are positioned to maintain the roll rate at 0° per second. This results in a constant bank angle.
• When the side stick is displaced laterally, increasing roll rates are commanded. At full deflection, a roll rate of 15° per second is commanded in NORMAL LAW. The ailerons and spoilers are positioned as necessary to achieve the commanded roll rate.
• The side stick position cannot be used as a reference to determine the actual positions of flight control surfaces.
• In normal turns (up to 33°) pitch trim is automatic and assists the pilot in maintaining altitude (pitch inputs may still be needed to maintain altitude).
• If the bank is increased beyond 33° and the side stick is released, the aircraft would return to 33° of bank. This is known as positive spiral stability.
• Positive spiral stability is a characteristic programmed into the flight control computers, which returns the aircraft to a more stable condition (0° if high speed or angle-of-attack protection is active).
• Beyond 33°of bank, positive spiral stability is active and automatic pitch trim is inhibited. To maintain a bank angle greater than 33°, continuous side stick pressure must be used. Also, continuous back pressure will be needed to maintain altitude since automatic pitch trim is inhibited.

Question 37

The pilots find themselves in ALTERNATE LAW. Describe the indications and available protections, and flight control logic.

Answer 37

• In most cases, a single system of component failure will not cause a flight control degradation (jammed stabilizer causes a degradation).
• Indications would be amber Xs and an EW/D message. The ECAM states PROT LOST, but maneuver protection is still available.
• Autopilot availability in ALTERNATE LAW depends on the failures thatcaused the degradation. Generally speaking, if the failures DO NOT affect a primary flight control surface, the autopilot should be available.
• Pitch is the same as NORMAL LAW, roll is direct (not roll rate demand), and yaw loses turn coordination.
• Attitude, high speed, and angle of attack protections are lost. They are replaced by high speed stability and low speed stability, respectively.
• High speed stability activates just prior to the over speed warning. Nose down trim is inhibited.
• Low speed stability activates just prior to the stall warning. Nose up trim is inhibited.
• The pilot can override the stabilities and over speed or stall the aircraft.
• Instead of commanding a specific roll rate, there is a direct relationship
between side stick position and control surface position. As a result, roll sensitivity now changes with aircraft speed and amount of side stick deflection.
• Bank angle protection is not available in ALTERNATE LAW. Roll commands are carried out directly without modification.
• Depending on the failure combination, the maximum roll rate may be as much as twice as it was in NORMAL LAW.
• Attitude protection is lost and the green “=” signs on the PFD are replaced with amber Xs. There are now no limits on how far a pilot can pitch or roll the aircraft. The aircraft can roll beyond the amber Xs. Positive spiral stability is also lost.
• In ALTERNATE LAW, turn coordination is always lost regardless of FAC status. Yaw damping, rudder trim and rudder limiting is available if a FAC is operational.

Question 38

The pilots find themselves in DIRECT LAW. Describe the indications, protections, and flight control logic.

Answer 38

• When in ALTERNATE LAW, there is no landing mode that would provide consistent control during landing for all possible failure combinations. Consequently, the flight controls transition to DIRECT LAW when the landing gear is extended.
• DIRECT LAW is very unlikely in flight. It usually results from lowering the gear while in ALTERNATE LAW.
• An ECAM message is generated and says “PROT LOST”. Unlike in ALTERNATE LAW, this is now true. There are no protections or stabilities available in DIRECT LAW.
• The message “USE MAN PITCH TRIM” in amber is displayed on the FMA because automatic pitch trim is lost.
• Pitch control is direct. Load factor demand is lost. Pitch sensitivity or control is a factor of airspeed and the amount flight control deflection. Roll control is the same as ALTERNATE LAW (direct relationship with no protections).

Question 39

The pilots find themselves in MECHANICAL BACKUP. What functions are available?

Answer 39

• MECHANICAL BACKUP control is provided for the rudder and THS in the event of a complete loss of flight control computers or electrical power.
• Although the aircraft can be flown indefinitely in this condition, it is intended to be used only as long as it takes to restore the computers.
• Note the EW/D warning message and red “MAN PITCH TRIM ONLY” indication on the FMA. There isn’t a specific mechanical backup ECAM message.
• The side sticks are inoperative. Pitch is controlled with the trim wheel via the mechanical connection to the pitch system.
• Roll and yaw are controlled through the rudder pedals and the mechanical connection to the rudder.
• In reality, the failure of only four flight control computers may result in mechanical backup: Both ELACs and SEC 1 and 2 fail, all computerized pitch control is lost. In this case, because SEC 3 is still available, the side sticks can control roll using one spoiler on each wing, but pitch control is mechanical.