Flight control modes

[1][2][3][4] A reduction of electronic flight control can be caused by the failure of a computational device, such as the flight control computer or an information providing device, such as the Air Data Inertial Reference Unit (ADIRU).

In normal flight, the computers act to prevent excessive forces in pitch and roll.

[7] The flight mode of normal law provides five types of protection: pitch attitude, load factor limitations, high speed, high-AOA and bank angle.

Flight mode is operational from take-off, until shortly before the aircraft lands, around 100 feet above ground level.

When the stick is neutral and the load factor is 1g, the aircraft remains in level flight without the pilot changing the elevator trim.

Horizontal side stick movement commands a roll rate, and the aircraft maintains a proper pitch angle once a turn has been established, up to 33° bank.

[citation needed] Alpha protection (α-Prot) prevents stalling and guards against the effects of windshear.

There are two speed limitations for high altitude aircraft, VMO (maximum operational velocity) and MMO (maximum operational Mach) the two speeds are the same at approximately 31,000 feet, below which overspeed is determined by VMO and above which by MMO.

[citation needed] This mode is automatically engaged when the radar altimeter indicates 100 feet above ground.

All protections are lost, and the maximum deflection of the elevators is limited for each configuration as a function of the current aircraft centre of gravity.

[9] DIR is entered if there is failure of three inertial reference units or the primary flight computers, faults in two elevators, or flame-out in two engines (on a two-engine aircraft) when the captain's primary flight computer is also inoperable.

[3] The fly-by-wire electronic flight control system of the Boeing 777 differs from the Airbus EFCS.

The role of the PFC is to calculate the control laws and provide feedback forces, pilot information and warnings.

The design philosophy is: "to inform the pilot that the command being given would put the aircraft outside of its normal operating envelope, but the ability to do so is not precluded.

Full functionality is provided, including all enhanced performance, envelope protection and ride quality features.

[citation needed] Boeing secondary mode is comparable to the Airbus alternate law, with the PFCs supplying commands to the ACEs.

Modern aircraft designs like the Boeing 777 rely on sophisticated flight computers to aid and protect the aircraft in flight. These are governed by computational laws which assign flight control modes during flight
A330-200 in flight
Airbus A321 cockpit
Illustration of the air-data reference system on Airbus A330
A380 in take off
The cockpit of the 777 is similar to 747-400, a fly-by-wire control simulating mechanical control