Flight Controls [Question Bank Airbus A320] – Page 2

21. What all protections are available in Normal Law?

Normal law provide the following protections:

  • Load Factor Protection
  • Pitch Attitude Protection
  • High Angle of Attack Protection (this is different from Alpha Floor Protection)
  • High Speed Protection
  • Bank Angle Protection

22. Rudder has no protection available and must be used with care. Is this statement correct?

This statement is partially correct. Although rudder travel limiter is available still it is advisable to use rudder with care. There is no direct protection available for rudder input under Normal or any other law.

23. How are ground mode, rotation mode and flight mode different from each other?

Ground Mode Rotation Mode Flight Mode Flare Mode
  • direct relationship between side stick deflection and control surfaces without auto trim
  • it automatically sets THS at 0 degree
  • as aircraft reaches 75 kt during take off maximum up elevator deflection reduces from 30 degree to 20 degree
  • provides homogeneous rotation for all weight, CG and config while minimizing risk of tail strike
  • active from 70 kt during takeoff roll until 10 s after lift off
  • load factor demand mode with auto-trim available
  • passing 50 feet RA, THS is frozen and flare mode become active
  • system memorize aircraft attitude at 50 feet and become initial reference for pitch attitude control
  • as aircraft descend through 30 feet system begins to reduce pitch attitude by -2 degree nose down over period of 8 seconds.

24. Under what all conditions automatic pitch trim freezes?

Automatic pitch trim freezes in following situations:

  • Manual trim input is given
  • RA is below 50 ft (100 ft with AP ON)
  • Load factor goes below 0.5 g

25. Under what all conditions THS setting gets limited?

Under following conditions THS setting gets limited. Neither pilot NOR system can apply additional destructive nose trim input:

  • When angle of attack protection is active – THS setting is limited between the setting at aircraft entry into this protection and 3.5 degree nose down. (no pitch up input possible)
  • When load factor is higher than 1.25 g or bank angle of 33 degree, THS setting is limited to values between actual setting and 3.5 degree nose down
  • When high speed or high mach protection is active, THS setting is limited between the setting at aircraft entry into this protection and 11 degree nose up

26. Explain load factor protection limits.

Under normal law aircraft  has following load factor protection limits:

  • +2.5 g to -1 g (in clean configuration)
  • +2 g to 0 g (other configuration)

27. What pitch attitude protections are available under normal law?

Following limits are applicable to pitch attitude under normal law:

  • 30 degree nose up in config 0 to 3 (progressively reduced to 25 degree at low speed)
  • 25 degree nose up in config FULL (progressively reduced to 20 degree at low speed)
  • 15 degree nose down
  • green = = symbols are present on PFD to indicate these limits

28. Explain the concept of  high angle of attack protection.

HIGH ANGLE OF ATTACK PROTECTION

When AOA increases above alpha-PROT, high angle of attack protection activates.

  • without pilot’s input flight control maintains angle of attack equal to alpha PROT
  • with pilot’s input maximum angle of attack equal to alpha max can be maintained
  • when high angle of attack protection is active normal law demand is modifies to correlate side stick input to angle of attack demand instead of load factor demand (angle of attack can be varied between alpha PROT and alpha Max)

alpha protection and alpha max

29. Pilot can make gentle turn while holding control stick full aft (assuming aircraft under normal law). Is this statement correct?

Yes this statement is correct. Under this condition angle of attack protection will be active. Aircraft will maintain alpha max which is less than alpha CL max (stalling angle) hence some margin is available for maneuvering the aircraft.

30. How can high angle of attack protection be deactivated?

To deactivate angle of attack protection pilot must push sidestick:

  • greater than 8 degree forward OR
  • greater than 0.5 degree for at least 0.5 s when alpha is less than alpha Max

In addition, below 200 ft, angle of attack protection is also deactivated, when: 

  • sidestick deflection is less than half nose up
  • actual alpha is less than alpha protection – 2 degree

31. What is alpha MAX and alpha PROT?

alpha PROT alpha MAX
It is the angle of attack above which high angle of attack protection becomes active and also aircraft maintains this angle when  side stick is in neutral position and protection is active It is the maximum angle of attack aircraft can achieve in normal law. Gentle turns are possible at alpha max angle.

32. Explain High Speed Protection.

Depending on flight conditions high speed protection is activated at or above VMO or MMO. This is designed for aircraft automatically recovery following high speed upset. Following are the key points for High Speed Protection:

  • when activated, THS setting is limited between the setting at the aircraft’s entry into protection and 11 degree nose up
  • positive spiral stability is introduced to 9 degree bank angle (instead of 33 degree in normal law) – when side stick is released, aircraft returns to bank angle of – degree
  • bank angle limit is reduced from 67 degree to 40 degree
  • as aircraft speed increases above VMO/MMO, sidestick nose down authority is progressively reduced, and a permanent nose up order is applied to aid recovery to normal flight conditions. (aircraft slightly overshoot VMO/MMO and fly back towards envelope)
  • if side stick is maintained full forward, aircraft significantly overshoot VMO/MMO. At approximately VMO +16/MMO +0.04, pitch nose-down authority is smoothly reduces to zero
  • high speed protection is deactivated when aircraft speed decreases below VMO/MMO and usual normal control laws are recovered
  • autopilot disconnects at VMO +15 kt and MMO +0.04

33. How is high speed protection symbol indicated?

High speed protection symbol is indicated by two green bars at VMO +6

34. How does lateral control behave under normal law in flight, ground and flare mode?

  • Flight Mode: Amount of control surface deflection that results from given amount of sidestick deflection depends on aircraft speed and maximum of 15 degree per second can be achieved
  • Flare Mode: In flare mode lateral control acts in same way as flight mode
  • Ground Mode: After touch down aircraft smoothly transit from in flight to ground mode. (direct control stick to control surface relation)

35. Explain bank angle protection available in normal law.

  • aircraft maintains positive spiral static stability for bank angles above 33 degree (bank angle automatic reduces to 33 degree if pilot release side stick at bank angle greater than 33 degree)
  • up to 33 degree, system hols the bank angle when side stick is neutral
  • maximum of 67 degree bank angle can be achieved with full sidestick deflection
  • if bank angle exceeds 45 degree, autopilot disconnects and FD bars disappear, FD bars return when bank angle decreases to less than 40 degree
  • when angle of attack protection is active maximum bank angle will not go beyond 45 degree
  • when high speed protection is active bank angle will not go beyond 40 degree

36. What is the normal range of rudder trim indication?

When aircraft is in normal cruise range (around M .77), with AP ON, symmetrical engine thrust and symmetrical fuel distribution, rudder trim should stay between 1 degree right and 2.3 degree left. Indicated rudder trim beyond this range is acceptable only if maintenance personal establishes that corresponding real rudder position is withing 1.5 degree left and 1.5 degree right.

37. What are the protections available in when aircraft is in alternate law?

Pitch Control Lateral Control
  • Flight Mode: same load factor demand as in normal law with reduced protections
  • Flare Mode: flight mode changes to flare mode when landing gear down
  • Ground Mode: becomes active on ground 5 seconds after touch down, same as normal law
  • Roll direct law (direct sidestick to control surface relation)
  • Yaw alternate law – yaw damping is available, damper authority is limited to +-5 degree of rudder deflection

38. What all reduced protections are available in flight control alternate law?

Following reduced protections are available in flight control alternate law:

  • Load Factor Limitation – same as normal law
  • Low speed stability – gentle nose down signal is introduced 5-10 kt above VSW, this can be overridden (STALL STALL & crickets nose is available)
  • High speed stability – above VMO and MMO nose up demand is introduced, this can be overridden, aural warning at VMO +4 and MMO + 0.006 is available

39. Only load factor protection is available in direct law. Is this statement correct?

Yes

40. What are ECAM indications for alternate and direct law?

Alternate Law Direct Law
FLT CTL ALTN LAW (PROT LOST)
MAX SPEED  320 kt
FLT CTL DIRECT LAW (PROT LOST)
MAX SPEED 320 kt
MAN PITCH TRIM USE