What is lost when
FCOM DSC-27-20-10 · DSC-27-20-20 P 10–22
| Function | Normal | Alternate | Direct |
|---|---|---|---|
| Pitch | Load factor demand, auto trim | Load factor demand, auto trim | Stick to elevator, manual trim |
| Roll | Roll rate demand, 15°/s maximum | Stick to surface, about 30°/s clean | |
| Yaw | Turn coordination and yaw damping | Yaw damping only | Pedals only |
| Load factor | +2.5 to −1 g clean, +2 to 0 g otherwise | None | |
| Pitch attitude | 30° up, 15° down | None, or a limitation in clean | None |
| Low speed | High AOA protection, alpha floor | Low speed stability, no alpha floor | Stall warning only |
| High speed | High speed protection | High speed stability | Overspeed warning only |
| Bank angle | 33° held, 67° maximum | None | |
| Gear down | Flare mode near the ground | Pitch changes to direct law | No change |
- PFD: amber crosses replace the green protection symbols.
- PFD: amber USE MAN PITCH TRIM when auto trim is lost.
- ECAM, alternate: FLT CTL ALTN LAW (PROT LOST), maximum 320 kt.
- ECAM, direct: FLT CTL DIRECT LAW (PROT LOST), maximum 320 kt / M 0.77, MAN PITCH TRIM USE.
Computers and surfaces
FCOM DSC-27-10-10 P 1–4
- 2 ELAC
- Elevators, stabilizer, ailerons
- 3 SEC
- Spoilers, standby elevators and stabilizer
- 2 FAC
- Electrical rudder control
- 2 FCDC
- Data to the displays and maintenance
- Every surface: electrical command, hydraulic actuation.
- Mechanical path: stabilizer through the trim wheels, rudder through the pedals.
- The two sidesticks are not coupled.
- Protections act in pitch and roll only, never on the rudder.
Normal law
FCOM DSC-27-20-10-20 P 1–9 · DSC-27-20-10-30 P 1–2
- Ground mode
- Stick to elevator, no auto trim
- Flight mode
- Load factor demand, auto trim
- Flare mode
- From 50 ft RA, stabilizer frozen
- Stick neutral, wings level
- 1 g, corrected for pitch
- Turns without pitch input
- Up to 33° of bank
- Maximum roll rate
- 15°/s
- Auto trim stops below
- 50 ft RA, 100 ft with AP
- Auto trim stops under
- 0.5 g
- Stick released: flight path and bank are held, and the aircraft trims itself.
- No rudder needed in turns: turn coordination and dutch roll damping are automatic.
- Auto trim also stops on manual trim and in high speed protection.
- Flare: attitude memorised at 50 ft, then lowered 2° over 8 s from 30 ft, so pull gently.
- Some standards enter flare mode at 100 ft.
Normal law protections
FCOM DSC-27-20-10-20 P 10–17 · DSC-27-20-10-30 P 3
- Load factor, clean
- +2.5 to −1 g
- Load factor, slats or flaps out
- +2 to 0 g
- Pitch up, CONF 0 to 3
- 30°, 25° at low speed
- Pitch up, CONF FULL
- 25°, 20° at low speed
- Pitch down
- 15°
- Bank, stick released
- Held to 33°, then back to 33°
- Bank, full stick
- 67°
- Bank, in AOA or pitch protection
- 45°
- Bank, in high speed protection
- 40° or 20° by standard
- Nose-down authority gone at
- About VMO + 16 kt / MMO + 0.04
- Overspeed warning
- VMO + 4 kt / MMO + 0.006
- Autopilot off
- Above 45° bank or VMO + 15 kt
- High AOA protection has priority over all the others.
- Above alpha prot the stick commands angle of attack: released, it holds alpha prot; full back, alpha max, just below the 1 g stall.
- Nose-up trim is inhibited in alpha prot.
- Alpha floor usually sets TOGA just after alpha prot. To exit, ease the stick forward, then cancel alpha floor with the instinctive disconnect.
- High speed: a nose-up order brings the aircraft back; released, the bank returns to wings level.
- With the autopilot engaged, every protection stays except pitch attitude.
- Not structural limits: no deliberate excursions, no opposite rudder inputs.
Alternate law
FCOM DSC-27-20-20 P 10–21
- Pitch
- Load factor demand, auto trim
- Roll
- Direct law
- Yaw damper authority
- ±5° of rudder
- Load factor limitation
- As in normal law
- Low speed stability starts
- 5 to 10 kt above stall warning
- High speed stability starts
- Above VMO / MMO
- Alpha floor
- Lost
- Bank angle protection
- Lost
- Landing gear down
- Pitch changes to direct law
- Gear position unknown
- Direct law from CONF 2
- Protections become stabilities the crew can override.
- Near the stall: gentle nose-down order, red and black barber pole, aural STALL warning.
- Some standards add a pitch limitation in clean (about 20° at sea level to 8° at maximum altitude) and a BANK BANK alert above 45°. Neither prevents a stall.
- Without reduced protection, only the load factor limitation remains.
- The autopilot disconnects above VMO / MMO or 45° of bank.
Direct law
FCOM DSC-27-20-20 P 22
- Pitch
- Elevator proportional to stick
- Pitch trim
- Manual
- Roll rate, clean
- About 30°/s
- Roll rate, slats out
- About 25°/s
- Roll surfaces
- Ailerons, spoilers 4 and 5
- Yaw
- Pedals, no yaw damping
- Maximum elevator deflection depends on the CG.
- No protection, no alpha floor. Overspeed and stall warnings remain.
- Spoiler 3 replaces a failed spoiler 4. With the ailerons failed, all roll spoilers are used.
- No turn coordination: use the pedals.
Which failure, which law
FCOM DSC-27-20-20 P 3–9
| Failure | Pitch law | Yaw |
|---|---|---|
| Both ELACs | Alternate | Alternate |
| All three SECs | Alternate | Alternate |
| Two ADRs or IRs, second self-detected | Alternate | Alternate |
| Green and yellow hydraulics | Alternate | Mechanical |
| Green and blue hydraulics | Alternate, no reduced protection | Alternate |
| Both SFCC slat channels | Alternate, no reduced protection | Alternate |
| All three ADRs | Alternate, no reduced protection | Mechanical |
| All three IRs | Direct | Mechanical |
| Both radio altimeters, at gear extension | Direct | Alternate |
| Batteries only | Alternate | Mechanical |
| Emergency generator | Alternate | Alternate after FAC 1 reset |
- Roll is direct in every row.
- A single failure keeps normal law, so the table starts at double failures.
- Reconfiguration depends on the aircraft standard. Check your own FCOM.
Abnormal attitude law and mechanical backup
FCOM DSC-27-20-20 P 23–24
- Bank
- Above 125°
- Pitch, two air data sources valid
- Above 50° up or 30° down
- Pitch, otherwise
- Above 40° up or 20° down
- Speed
- Below 70 to 90 kt or above 440 kt
- Mach
- Above 0.91
- Angle of attack
- Above 40°
- Engaged: pitch alternate with no protection at all, roll direct, yaw mechanical, no auto trim. ECAM shows DIRECT LAW.
- After recovery: alternate law without reduced protection for the rest of the flight.
- Mechanical backup: pitch with the trim wheel, roll and yaw with the pedals, red MAN PITCH TRIM ONLY.
- It covers a temporary total electrical loss, five computers lost or both elevators lost.
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Questions about A320 flight control laws
What is the difference between normal, alternate and direct law?
In normal law the sidestick commands a load factor in pitch and a roll rate in roll, with full flight envelope protection. Alternate law keeps the pitch load factor demand but flies roll in direct law and replaces most protections with weaker stabilities. Direct law moves the surfaces in proportion to the sidestick, with no protection and no automatic pitch trim.
When does alternate law change to direct law?
When the landing gear is selected down, pitch control changes from alternate to direct law, so the landing is flown with manual pitch trim. If landing gear information is lost, the change happens at CONF 2 instead.
What is the maximum bank angle in normal law?
With full lateral sidestick the bank angle stops at 67°. With the sidestick released the aircraft holds any bank up to 33° and rolls back to 33° from beyond it. In high angle of attack or pitch attitude protection the maximum is 45°.
Do the protections stay active with the autopilot engaged?
Yes, all normal law protections remain active except pitch attitude protection. The autopilot disconnects above 45° of bank and at about VMO + 15 kt or MMO + 0.04.