Aside-stick orsidestick controller is anaircraft control stick that is located on the side console of thepilot, usually on the righthand side, or outboard on a two-seatflightdeck. Typically this is found in aircraft that are equipped withfly-by-wire control systems.[1]
The throttle controls are typically located to the left of a single pilot or centrally on a two-seat flightdeck. Only one hand is required to operate them; two-handed operation is neither possible nor necessary.
The side-stick is used in many modern militaryfighter aircraft, such as theF-16 Fighting Falcon,Mitsubishi F-2,Dassault Rafale, andF-22 Raptor,F-35 Lightning 2,Chengdu J-20,AIDC F-CK 1 Ching-Kuo and also on civil aircraft, such as theSukhoi Superjet 100,Airbus A320 and all subsequentAirbus aircraft,[2] including the largest passenger jet in service, theAirbus A380.
It is also used in new helicopter models such as theBell 525.
A side-stick arrangement contrasts with the more conventional design where the stick is located in the centre of the cockpit between the pilot's legs, called a "centre stick". A side-stick arrangement allowsHOTAS and increasesejection seat safety for the pilot as there is less interference amongst flight controls.[citation needed]
In Airbus's implementation, input values of both side-sticks are normally added up,[3] except when the "priority takeover button" is held down. In such a scenario, any inputs on the other side-stick will be ignored.[4] Holding this button down for a minimum of 40 seconds will result in the other side-stick being disabled. This can reversed by pressing the button on either side-stick again. A green light will activate on the side of the pilot currently on control. In contrast, on the side of the other pilot, a red light will turn on to indicate that their side-stick's inputs are being ignored.[5]
While the inputs are added up, the sum isclamped to the value of the maximum possible deflection a single side-stick;[6] but this still means that when both side-stick are deflected 50% in the same direction, the resulting effective input will be that of a fully deflected side-stick, despite neither one being deflected over 50%. In addition, because the inputs are added up, any deflection of the other side-stick in the opposite direction will in effect be subtracted, resulting in the inputs partially cancelling each other out. In fact, if two inputs have opposite directions but equal magnitudes, the sum will be zero, and thus the flight control surfaces would remain in their current positions.
In addition to visual indications,[7] detection of more than a single side-stick deflection greater than 2°[8] from neutral without the priority takeover button being held down results in an aural "DUAL INPUT" warning being played every five seconds.[9] Due to this aural warning having the lowest priority, it will not be played if there are warnings with a higher priority, such as those from theEGPWS, as those will take precedence,[10] posing a potential risk for pilots.Examples of this occurring include the 2009 crash ofAir France Flight 447 (anAirbus A330 flying fromRio de Janeiro toParis), the 2010 crash ofAfriqiyah Airways Flight 771 an Airbus A330 from flyingJohannesburg toTripoli[11][12] and the 2014 crash ofIndonesia AirAsia Flight 8501 (anAirbus A320 flying fromSurabaya toSingapore).[13][14].
In the centre stick design, like traditionalairplane yokes, both the pilot flying, PF's, and pilot not flying, PNF's, controls are mechanically connected together so each pilot has a sense of the control inputs of the other.
In aircraft with passive side-sticks, on the other hand, they move independently from each other, and do not offer any haptic feedback on what the other pilot is inputting. This can lead to "dual input" situations, which should be avoided(see:§ Handling of dual input situations).
However a later, significant, development is the "active" side-stick,[15] used in theGulfstream G500/G600 series business jet aircraft. In this system, movements in one side-stick produce the same actions in the other side-stick and therefore provide valuable feedback to the other pilot. This addresses the earlier criticisms of the "passive" side-stick. The active side-stick also provides tactile feedback[16] to the pilot during manual flight. In 2015, the three largest avionics manufacturers – Honeywell, Rockwell Collins and Thales[17] – were predicting this would become the standard for all newfly-by-wire aircraft. In 2015,Ratier-Figeac, a subsidiary ofUTC Aerospace Systems and supplier of passive side-sticks to Airbus since the 1980s,[18] became the supplier of active side-sticks for theIrkut MC-21.[19] This is the firstairliner to use them.
Such an active side-stick can also be used to increase adherence to a safe flight envelope by applyingforce feedback when the pilot makes a control input that would bring the aircraft closer to (or beyond) the borders of the safe flight envelope. This reduces the risk of pilots entering dangerous states of flight outside the operational borders while maintaining the pilots' final authority and increasing theirsituational awareness.[20]
The two sidesticks are not mechanically linked as they are on older types of aircraft. This means that both sticks may be operated independently one of the other. When one sidestick is operated it sends an electrical signal to the Fly By Wire computers. When both sticks are moved simultaneously, the system adds the signals of both pilots algebraically.
To avoid both signals being added by the system, a priority P/B is provided on each stick. By pressing this button, a pilot may cancel the inputs of the other pilot. An audio signal will indicate which sidestick has priority.
A green light will come on in front of the pilot who has taken control if the other stick is not in neutral popsition, and a red light comes on in front of the pilot whose stick is deactivated.
The total is limited to the signal that would result from the maximum deflection of a single sidestick.
When a dual input situation is detected, the two green priority lights located on the cockpit front panel flash simultaneously. The visual indication is an ADVISORY of a dual input situation
In order to warn the crew in case of dual sidestick operations, Airbus has designed a package of dual input indicators and audio warning. These operate when both side sticks are deflected simultaneously by more than 2°.
After the visual indication has been triggered, a synthetic voice "DUAL INPUT" comes up every 5 sec, as long as the dual input condition persists. The synthetic voice is a WARNING of a dual input situation.
Note: This audio has the lowest priority among the synthetic voice audio alerts.
It seems surprising that Airbus has conceived a system preventing one pilot from easily assessing the actions of the colleague beside him. And yet that is how their latest generations of aircraft are designed. The reason is that, for the vast majority of the time, side-sticks are superb.