A330/A340 2.60.1 Flight Controls
FCTM REV 1 (6 JUN 05)
GENERAL
The Airbus flight control surfaces are moved by commands from several flight control computers in response to pilot input. This system is referred to as "fly-by-wire" as there is no mechanical connection between the sidestick and the control surfaces. The relationship between sidestick input and the aircraft response is called the flight control law. Depending upon the status of the fly-by-wire system, three sets of control laws are provided, i.e. Normal Law, Alternate Law and Direct Law. In the unlikely event of a failure causing a complete loss of the fly-by-wire system, the aircraft can be flown safely through a backup system while the crew complete actions to recover one of the control laws.
Each law has a set of protections and/or warnings which are discussed below.
NORMAL.LAW
Under most circumstances, the aircraft is operated in Normal Law. Normal law is designed to accommodate single system failures and has three modes:
. Ground Mode . Flight Mode . Flare Mode
The transition from one mode to the next is transparent to the pilot.
Ground.Mode
On the ground and at low speeds, the sidesticks have full authority over the controls in pitch and roll. Ground mode is progressively blended out after take-off as the flight mode becomes active.
When the aircraft is on the ground, the PFD includes a symbol (1) that is the sum of the sidestick positions given to the flight control computers. It permits the PNF to check that the PF is making the appropriate control input during the take-off roll.
Small limit marks (2) indicate the limits of stick travel (±16° in pitch, ±20° in roll).
Do not use this display for flight control checks because it does not indicate flight control position.
2.60.2
A330/A340 General Information REV 1 (6 JUN 05)
FCTM Flight Controls
Flight.Mode
In pitch, when an input is made on the sidestick, the flight control computers interpret this input as a “g” demand/pitch rate. Consequently, elevator deflection is not directly related to sidestick input. The aircraft responds to a sidestick order with a pitch rate at low speed and a flight path rate or “g” at high speed. When no input is made on the sidestick, the computers maintain a 1g flight path. Pitch changes due to changes in speed, thrust and/or configuration, which in a conventional aircraft would require the pilot to re-trim the aircraft, are compensated for by the computers repositioning the THS. The pitch trim wheel moves as the control law compensates for these changes. Sometimes, changes of trim due to changes in thrust may be too large for the system to compensate, and the aircraft may respond to them in pitch in the conventional sense and then hold the new attitude at which it has stabilised after the trim change.
Due to its neutral static stability, the aircraft maintains the selected flight path. Should it deviate however, only small sidestick inputs are required to regain the desired flight path.
A330/A340 2.60.3 Flight Controls
FCTM REV 1 (6 JUN 05)
In roll, when an input is made on the sidestick, the flight control computers interpret this input as a roll rate demand. Consequently, aileron and/or spoiler deflection is not directly related to sidestick input. When no input is made on the sidestick, the computers maintain a zero roll rate. At bank angles less than 330 with no input being made on the sidestick, the computers maintain a zero roll rate and, consequently, the aircraft will maintain a constant bank angle. Within this range, there is no need to make a correction in pitch, as this will be compensated for by the computers. Beyond 330 angle of bank, pitch compensation is no longer available. On releasing the sidestick to neutral, the aircraft rolls back to 330angle of bank.
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