FLIGHT CONTROL LAWS

Question 1

What are the different Control laws and their characteristics ?

Answer 1

• Normal law
  • Pitch: Vertical load factor
  • Bank: Roll rate
• Alternate law
  • Pitch: Vertical load factor
  • Bank: Roll rate in ALTN1 / Direct control of ailerons in ALTN2
• Direct law
  Direct relationship between stick and flight control surfaces
• Ground law (before lift-off and after touch-down):
  Same as Direct law
• Flare law (allow conventional flare):
  • Pitch: Stick orders a pitch attitude increment to a reference attitude
  • Bank: Direct control of ailerons

Question 2

What are the protections in normal law ?

Answer 2

• Load factor protection
• High speed protection
• High angle-of-attack protection
• Pitch attitude protection
• Bank angle protection
• Low energy warning

Question 3

What protections are available in alternate law?

Answer 3

• Load factor protection
• Bank angle protection (in ALTN1 only)
• Low speed stability:
  • VSW replaces αPROT and αMAX
  • When speed reduces to VSW, AP disconnects and a nose down pitch input is introduced
• High speed stability:
  • Amber dashes replaces the Green dashes on speed scale
  • When speed increases to VMO, AP disconnects and a nose up pitch input is introduced
• Aural stall
• Overspeed warning

Question 4

What protections are available in Alternate law without stability ?

Answer 4

• Load factor protection
• Aural stall
• Overspeed warning

Question 5

Load factor protection

Answer 5

Load factor limitation :
+ 2.5 g, -1 g for clean configuration
+ 2 g, 0 g when slats are extended

Rapid pull-up to 2.5 g is immediately possible.

Question 6

High speed protection

Answer 6

- VMO + 4 kt /  MMO+ 0.006:
Overspeed Ecam warning 
- VMO +6 kt / MMO + 0.01:
Automatic, progressive pitch up applied (.1 g max)
Pilot nose-down authority reduced.

Maximum stabilized speed with stick maintained nose-down : VMO + 16 kt / MMO +0.04

Question 7

High angle-of-attack protection

Answer 7

• VLS: Minimum allowed speed, A/THR in speed mode will not allow the speed to drop below VLS even if lower speed is selected.
• Vα Prot: AP disengages, Auto Pitch trim stops
• Vα Floor: TOGA thrust is automatically set
• Vα Max: Speed is maintained with full aft stick, speed brake retract if previously extended

Question 8

Pitch attitude protection

Answer 8

Pitch attitude limited :

• nose-down 15°
• nose-up 30°, to 25° at low speed

Question 9

Bank angle protection

Answer 9

• Bank angle limited to 67°
• Above 33° :
  . Stick released, aircraft rolls back to 33°
  . Stick maintained, bank angle maintained
• When overspeed protection is triggered :
  . Spiral stability is introduced regardless of angle
  . Max bank angle is limited to 45°
• When angle-of-attack protection is triggered:
  . Max bank angle is limited to 45°

Question 10

Low energy warning

Available between 100 ft and 2000 ft RA
Conf 2, 3 and Full

Answer 10

Aural warning, “SPEED SPEED SPEED” :

Informs the pilot that the aircraft energy becomes lower than a threshold under which, to recover a positive flight path angle through pitch control, the thrust must be increased.

Question 11

What protections are available in Direct law ?

Answer 11

• Aural stall

- Overspeed warning