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{{Short description|Aircraft control computer software}}
[[File:Aeroflot Boeing 777 inflight.jpg|thumb|upright=1.14|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.]]▼
A '''flight control mode''' or '''flight control law''' is a computer software algorithm that transforms the movement of the [[Yoke (aeronautics)|yoke]] or [[joystick]], made by an aircraft pilot, into movements of the aircraft control surfaces. The control surface movements depend on which of several modes the flight computer is in. In aircraft in which the [[Aircraft
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 [[
▲[[File:Aeroflot Boeing 777 inflight.jpg|thumb|upright=1.14|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]]
▲Aircraft with [[fly-by-wire]] flight controls usually have automatic flight control modes, in which flight control laws<ref>{{Cite web|url=https://www.skybrary.aero/index.php/Flight_Control_Laws|title=Flight Control Laws - SKYbrary Aviation Safety|website=www.skybrary.aero|access-date=2019-07-03}}</ref><ref>{{Cite web|url=https://leehamnews.com/2016/03/25/bjorns-corner-flight-control-part-3/|title=Flight control part 3|website=Bjorn's corner}}</ref> determine the functional transformation of input signals, read from sensors and other sources, to output signals, feeding actuators and other destinations; they are an application of [[Mode (user interface)|modes in user interfaces]]. Their purpose is to modify the way in which human control inputs are translated to the [[flight control surfaces]], and ultimately its path of movement, in a way appropriate to different situations or flight regimes.<ref name="urlCrossing the Skies » Fly-by-wire and Airbus Laws">{{cite web |url=http://www.crossingtheskies.com/fly-by-wire-airbus-laws/ |title=Crossing the Skies » Fly-by-wire and Airbus Laws |work= crossingtheskies.com|accessdate=|archiveurl = https://web.archive.org/web/20090308133740/http://www.crossingtheskies.com/fly-by-wire-airbus-laws/|archivedate =8 March 2009}}</ref><ref name="Boeing 777">{{cite web |url=http://euler.ecs.umass.edu/ece655/Boeing777.ppt |title=The Boeing 777 |format=powerpoint |work= by Saurabh Chheda |accessdate=}}</ref>
▲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 [[ADIRU]].<ref name="Skybrary: Flight Control Laws">{{cite web |url=http://www.skybrary.aero/index.php/Flight_Control_Laws |title=Skybrary: Flight Control Laws}}</ref>
[[Aircraft flight control systems|Electronic flight control systems]] (EFCS) also provide augmentation in normal flight, such as increased protection of the aircraft from overstress or providing a more comfortable flight for passengers by recognizing and correcting for [[turbulence]] and providing [[yaw damper|yaw damping]].{{Citation needed|date=October 2013}}
Two aircraft manufacturers produce commercial passenger aircraft with primary flight computers that can perform under different flight control modes
These newer aircraft use electronic control systems to increase safety and performance while saving aircraft weight. These electronic systems are lighter than the old mechanical systems and can also protect the aircraft from overstress situations, allowing designers to reduce over-engineered components, which further reduces the aircraft's weight.{{Citation needed|date=October 2013}}
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[[File:Gulfair.a330-200.a40-kc.arp.jpg|thumb|right|A330-200 in flight]]
Airbus aircraft designs after the [[Airbus A300|A300]]/[[Airbus A310|A310]] are almost completely controlled by fly-by-wire equipment. These newer aircraft, including the [[Airbus A320 family|A320]], [[Airbus A330|A330]], [[Airbus A340|A340]], [[Airbus A350|A350]] and [[Airbus A380|A380]] operate under Airbus flight control laws.<ref name="SmartCockpit - A330 Flight Controls">{{cite web|url=http://www.smartcockpit.com/pdf/plane/airbus/A330/systems/0010/ |title=Airbus 330 – Systems – Flight Controls |work=SmartCockpit – Airline training guides, Aviation, Operations, Safety |
[[File:Airspeed indication system - fly by wire.png|thumb|Illustration of the
The aircraft is controlled by three primary control computers (captain's, first officer's, and standby) and two secondary control computers (captain's and first officer's). In addition there are two flight control data computers (FCDC) that read information from the sensors, such as air data (airspeed, altitude). This is fed along with GPS data, into three [[redundancy (engineering)|redundant]] processing units known as [[air data inertial reference unit]]s (ADIRUs) that act both as an air data reference and inertial reference. ADIRUs are part of the air data inertial reference system, which, on the Airbus is linked to eight [[air data module]]s: three are linked to [[pitot tubes]] and five are linked to static sources. Information from the ADIRU is fed into one of several flight control computers (primary and secondary flight control). The computers also receive information from the control surfaces of the aircraft and from the pilot's aircraft control devices and autopilot. Information from these computers is sent both to the pilot's primary flight display and also to the control surfaces.{{Citation needed|date=October 2013}}
There are four named flight control laws, however ''alternate law'' consists of two modes, ''alternate law 1'' and ''alternate law 2''. Each of these modes have different sub modes: ground mode, flight mode and flare, plus a back-up ''mechanical
===Normal law===
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====Ground mode====
The aircraft behaves as in direct mode: the autotrim feature is turned off and there is a direct response of the elevators to the sidestick inputs. The horizontal stabilizer is set to 4° up <!-- Stab nose up? Clarify--> but manual settings <!-- Manual settings, keyed in to the FMS? Clarify -->(e.g., for center of gravity) override this setting. After the wheels leave the ground, a 5-second transition occurs where ''normal law – flight mode'' takes over from ''ground mode''.<ref name="SmartCockpit - A330 Flight Controls"/>
====Flight mode====
The flight mode of ''normal law'' provides five types of protection: pitch attitude, load factor limitations, high speed, high-[[angle of attack|AOA]] and [[bank angle]]. ''Flight mode'' is operational from take-off, until shortly before the aircraft lands, around 100 feet above ground level. It can be lost prematurely as a result of pilot commands or system failures. Loss of ''normal law'' as a result of a system failure results in ''alternate law 1'' or ''2''.<ref name="urlAirbus Flight Control Laws">{{cite web |url=http://www.airbusdriver.net/airbus_fltlaws.htm |title=Airbus Flight Control Laws
Unlike conventional controls, in ''normal law'' vertical side stick movement corresponds to a load factor proportional to stick deflection independent of aircraft speed. 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. The system prevents further trim up when the [[angle of attack]] is excessive, the load factor exceeds 1.3g, or when the bank angle exceeds 33°.{{Citation needed|date=October 2013}}
Alpha protection (α-Prot) prevents stalling and guards against the effects of windshear. The protection engages when the angle of attack is between α-Prot and α-Max and limits the angle of attack commanded by the pilot's sidestick or, if autopilot is engaged, it disengages the autopilot.{{Citation needed|date=October 2013}}
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====Flare mode====
[[File:Airbus A380.jpg|thumb|right|A380 in take off]]
This mode is automatically engaged when the [[radar altimeter]] indicates 100 feet above ground. At 50 feet the aircraft trims the nose slightly down. During the [[landing flare]], ''normal law'' provides high-[[angle of attack
===Alternate law===
There are four reconfiguration modes for the Airbus fly-by-wire aircraft: ''alternate law 1'', ''alternate law 2'', ''direct law'' and ''mechanical law''. The ground mode and flare modes for ''alternate law'' are identical to those modes for ''normal law''.
'''Alternate law 1''' (ALT1) mode combines a ''normal law'' lateral mode with the load factor, bank angle protections retained. High angle of attack protection may be lost and low energy (level flight stall) protection is lost. High speed and high angle of attack protections enter
ALT1 may be entered if there are faults in the horizontal stabilizer, an elevator, yaw-damper actuation, slat or flap sensor, or a single air data reference fault.<ref name="SmartCockpit - A330 Flight Controls"/>
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===Direct law===
''Direct law'' (DIR) introduces a direct stick-to-control surfaces relationship:<ref name="SmartCockpit - A330 Flight Controls"/> control surface motion is directly related to the sidestick and rudder pedal motion.<ref name="urlCrossing the Skies » Fly-by-wire and Airbus Laws"/> The trimmable horizontal stabilizer can only be controlled by the manual trim wheel. 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. This aims to create a compromise between adequate pitch control with a forward
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.<ref name="SmartCockpit - A330 Flight Controls"/>
===Mechanical
In the ''mechanical
==Boeing 777
[[File:Boeing 777-200ER cockpit.jpg|thumb|right|The cockpit of the 777 is similar to 747-400, a fly-by-wire control simulating mechanical control.]]
The fly-by-wire electronic flight control system of the Boeing 777 differs from the Airbus EFCS. The design principle is to provide a system that responds similarly to a mechanically controlled system.<ref name="Boeing B-777: Fly-By-Wire Flight Controls">{{cite web |url=http://www.davi.ws/avionics/TheAvionicsHandbook_Cap_11.pdf |title=11 Boeing B-777: Fly-By-Wire Flight Controls
The electronic system is subdivided between
===Standard protections and augmentations===
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===Secondary mode===
Boeing ''secondary mode'' is comparable to the Airbus ''alternate law'', with the PFCs supplying commands to the ACEs. However, EFCS functionality is reduced, including loss of flight envelope protection. Like the Airbus system, this state is entered when a number of failures occur in the EFCS or interfacing systems (e.g., ADIRU or [[SAARU]]). Moreover, in case of a complete failure of all PFCs and ACEs, the ailerons and selected roll spoilers are connected to the pilot controls by control cable, permitting mechanical control on a temporary basis.<ref name="Skybrary: Flight Control Laws" /><ref name="Boeing 777"/>
==See also==
*[[Index of aviation articles]]
*[[Dual control (aviation)]]
==References==
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{{Aircraft components}}
[[Category:Technology systems]]▼
[[Category:Aircraft instruments]]▼
[[Category:Aerospace engineering]]
▲[[Category:Aircraft instruments]]
[[Category:Flight control systems]]
▲[[Category:Technology systems]]
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