Flight Controls Laws and Protections

Question 1

What is Normal law ?

Answer 1

During normal operation, the flight control logic protects the aircraft from exceeding the flight enveloppe.
The flight control characteristics and protections depend on the stage of the flight (ground - flight and flare modes)

Question 2

What is the GROUND mode ?

Answer 2

For pitch control :
- sidestick has direct stick to surface relationship

For roll :
- the sidestick controls the ailerons and spoilers 2-3-4 and 5

For yaw :
- the rudder pedals control the rudder

The THS is automatically resets to zero and no autotrim (pilot can manually sets the THS to the green band before takeoff)

Question 3

What is the maximum deflection of the elevator during takeoff in Ground mode ?

Answer 3

When speed reaches 70kt, the elevator deflection is reduced from 30° nose up to 20° nose up.

Question 4

When does the GROUND mode transition to FLIGHT mode ?

Answer 4

When pitch > 8°.
It takes 5 seconds for pitch and 0,5 seconds for roll

Question 5

What is the FLIGTH mode ?

Answer 5

For pitch control :
- sidestick is based on load factor demand. When sidestick at neutral, wings level, the load factor is maintained at 1g. Pitch trim is also automatic.

For roll :
- the sidestick commands a roll rate proportional to sidestick deflection. The maximum roll rate is 15°/sec when full deflection on the sidestick

Question 6

When does the FLIGHT mode transition to FLARE mode ?

Answer 6

It occurs upon landing when the aircraft reaches 50ft RA.
It takes 1 second to transition.

Question 7

What is the FLARE mode ?

Answer 7

The aircraft memorizes and maintains the pitch attitude through 50ft RA, then the pitch attitude is reduced to -2° nose down over a period of 8 seconds. This requires the pilot to gently flare the aircraft before touchdown.

Question 8

When does the FLARE mode transition to GROUND mode ?

Answer 8

After touchdown, when pitch < 2,5°, flare mode transitions to GROUND mode over a period of 5 seconds for pitch, and 0,5 second for roll.

Question 9

How many flight enveloppe protections in normal operations are there ?

Answer 9

5 protections in total :

• Load factor limitation
• Pitch attitude protection
• High AoA protection
• High speed protection
• Bank angle protection

Question 10

What is the Load Factor limitation ?

Answer 10

It limits the load factor to :

+2.5g to -1g in CLEAN configurations
+2g to 0 when flaps/slats extended

When load factor limitation is active, autotrim is inhibited or limited

Question 11

What is the Pitch attitude protection ?

Answer 11

It limits the pitch attitude to :

30° nose up in CONF 0 to 3 (progressively reduced to 25° at low speed)
25° nose up in CONF FULL (progressively reduced to 20° at low speed)
15° nose down in all configurations

Question 12

When do the FDs bars disappear/reappear with pitch attitude protection ?

Answer 12

They disappear when pitch exceeds 25° nose up or 13° nose down
They reappear when pitch goes below 22° nose up or 10° nose down

Question 13

What is the High AoA protection ?

Answer 13

In normal law, aircraft is protected against stall.
When the current AoA becomes greater than alpha prot, the protection activates.
The protection is active from liftoff to 100ft RA.

Question 14

What happens when AoA reaches V alpha prot ?

Answer 14

When AoA approaches V alpha prot, AP disconnects.
If the AoA reaches V alpha prot, the elevator switches to protection mode in which the AoA is proportional to sidestick deflection (instead of load factor demand)

Question 15

Can alpha MAX be exceeded in normal law ?

Answer 15

No, even with full backstick. When the sidestick is released, the AoA is reduced to maintain V alpha prot.

Question 16

What can we do to deactivate the pitch attitude protection ?

Answer 16

Push the sidestick more than 8° forward

Question 17

What happens if the pilot continues to pull the sidestick during the pitch attitude protection ?

Answer 17

At some point, the AoA continues to increase, until the Alpha Floor activates, which triggers full thrust regardless of the position of the thrust levers or the autothrust modes.

Question 18

When is Alpha Floor available ?

Answer 18

It is available from liftoff to 100ft RA.
It is NOT available in case of engine out when flaps/slats are extended to prevent VMC loss of control.

Question 19

What is the High Speed protection ?

Answer 19

It protects the aicraft for high speed buffet when exceeding VMO / MMO

Question 20

Where is displayed the high speed protection on the PFD ?

Answer 20

By the double green band at VMO +6kt

Question 21

What happens when speed exceeds VMO +6kt or MMO +0.01 ?

Answer 21

• AP disconnects
• Sidestick nose down demand is progressively reduced
  (if no input on the sidestick - aircraft will fly towards the flight enveloppe - pitch up effect)
  (if input sidestick forward - aircraft will limit VMO to VMO+16kt or MMO +0.04 with pitch autjority reduced to yzero)

Question 22

What is the Bank Angle protection ?

Answer 22

It protects the aircraft from high bank angle.
In normal operationm with wings level up to 33° bank, the bank is maintained if the sidestick is released. Autotrim is provied to maintain roll attitude.

If the bank is increased beyond 33° bank, positive static stability will bring the bank to 33° is sidestick is released. Autotrim will not trim anymore but will trim if pilot pushes down.

If the pilot holds full backstick, the bank will stop at 67°.

If the bank exceeds 45°, FD disappear and AP disconnects.

Question 23

When does the AP disconnect with the protection in normal law ?

Answer 23

High speed protection at VM0+15 or MMO+0.04
High AoA at V alpha prot threshold
Bank angle exceeds 45°

Question 24

What are the reconfiguration laws ?

Answer 24

Depending of the failures, there are 3 laws of reconfiguration :

• Alternate law (with and without reduced protections)
• Direct law
• Mechanical

Question 25

What is the difference between the Ground mode in Alternate law VS Normal law ?

Answer 25

No difference, there are identical

Question 26

What is the difference between the Flight mode in Alternate law VS Normal law ?

Answer 26

The aircraft follows a load factor demand similar to normal law but with reduced protections.
Pitch rate is limited to 5°/sec and roll rate is identical to Direct law (direct sidestick to surface relationship)

The maximum roll rate is 30°/sec in CLEAN conf and 25°/sec with slats extended.

Question 27

What is the difference between the Flare mode in Alternate law VS Normal law ?

Answer 27

It changes to FLARE mode when landing gear is down.

Question 28

What are the protections available in Alternate law ?

Answer 28

In alternate law with reduced protections :
- Load factor protection
- Low speed stability
- High speed stability

In alternate law without reduced protections :
- Load factor protection is only available

Question 29

What is the difference between the Load factor protection in Alternate law VS Normal law ?

Answer 29

No difference, there are identical

Question 30

What is the difference between the High AoA protection in Alternate law VS Normal law ?

Answer 30

High AoA protection is lost and is replaced by the Low Speed Stability

Question 31

What is the Low Speed Stability ?

Answer 31

The low-speed stability replaces the V alpha prot AoA protection.
The low speed scale is replaced with VSW.
Alpha floor mode is lost

Question 32

When is the low-speed stability available ?

Answer 32

Available for all slats/flaps configurations and is active from 5kt up to 10kt above stall warning speed (depending of the A/C weight)

Question 33

What does mean “USE MAN PITCH TRIM” ?

Answer 33

No autotrim is available ! Pilot must trim the aircraft

Question 34

What does mean “MAN PITCH TRIM ONLY” ?

Answer 34

During temporary and total loss of electricity, the pitch is controlled by using the THS wheel manually.
The roll is controlled by using the rudder pedals.