Side-stick

Prevalence

The side-stick is used in many modern military fighter aircraft, such as the F-16 Fighting Falcon, Mitsubishi F-2, Dassault Rafale, and F-22 Raptor, F-35 Lightning 2, Chengdu J-20, AIDC F-CK 1 Ching-Kuo and also on civil aircraft, such as the Sukhoi Superjet 100, Airbus A320 and all subsequent Airbus aircraft, including the largest passenger jet in service, the Airbus A380.

It is also used in new helicopter models such as the Bell 525.

Compared to centre sticks

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 allows HOTAS and increases ejection seat safety for the pilot as there is less interference amongst flight controls.

Handling of dual input situations

In Airbus's implementation, input values of both side-sticks are normally added up,{{cite web | work = Airbus Safety First #03 December 2006 p. 5/5 | series = Airbus Safety First Magazine | title = Dual Side Stick Inputs | date = 2024-11-23 | url = https://safetyfirst.airbus.com/app/themes/mh_newsdesk/documents/archives/dual-side-stick-inputs.pdf | quote = "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."}} except when the "priority takeover button" is held down, causing any inputs on the other side-stick to be ignored.{{cite web | work = Airbus Safety First #03 December 2006 p. 5/5 | series = Airbus Safety First Magazine | title = Dual Side Stick Inputs | date = 2024-11-23 | url = https://safetyfirst.airbus.com/app/themes/mh_newsdesk/documents/archives/dual-side-stick-inputs.pdf | quote = "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."}} Holding this button down for a minimum of 40 seconds will disable the other side-stick, which can be reversed by pressing the button on either side-stick again. If one stick is disabled a red light will show on it, and a green light on the active one.{{cite web | work = Airbus Safety First #03 December 2006 p. 5/5 | series = Airbus Safety First Magazine | title = Dual Side Stick Inputs | date = 2024-11-23 | quote = "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." | url = https://safetyfirst.airbus.com/app/themes/mh_newsdesk/documents/archives/dual-side-stick-inputs.pdf}}

While the inputs are added up, the sum is clamped to the value of the maximum possible deflection a single side-stick;{{cite web | work = Airbus Safety First #03 December 2006 p. 5/5 | series = Airbus Safety First Magazine | title = Dual Side Stick Inputs | date = 2024-11-23 | url = https://safetyfirst.airbus.com/app/themes/mh_newsdesk/documents/archives/dual-side-stick-inputs.pdf | quote = "The total is limited to the signal that would result from the maximum deflection of a single sidestick."}} but this still means that when both side-sticks are deflected 50% in the same direction, the resulting effective input will be that of a fully deflected side-stick. Also, because the inputs are added, 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. For example, if two inputs have opposite directions but equal magnitudes, the sum will be zero, and the flight control surfaces will not move.

In addition to visual indications,{{cite web | work = Airbus Safety First #03 December 2006 p. 5/5 | series = Airbus Safety First Magazine | title = Dual Side Stick Inputs | date = 2024-11-23 | url = https://safetyfirst.airbus.com/app/themes/mh_newsdesk/documents/archives/dual-side-stick-inputs.pdf | quote = "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"}} detection of more than a single side-stick deflection greater than 2°{{cite web | work = Airbus Safety First #03 December 2006 p. 5/5 | series = Airbus Safety First Magazine | title = Dual Side Stick Inputs | date = 2024-11-23 | url = https://safetyfirst.airbus.com/app/themes/mh_newsdesk/documents/archives/dual-side-stick-inputs.pdf | quote = "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°."}} from neutral without the priority takeover button being held down results in an aural "DUAL INPUT" warning repeated every five seconds.{{cite web | work = Airbus Safety First #03 December 2006 p. 5/5 | series = Airbus Safety First Magazine | title = Dual Side Stick Inputs | date = 2024-11-23 | url = https://safetyfirst.airbus.com/app/themes/mh_newsdesk/documents/archives/dual-side-stick-inputs.pdf | quote = "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."}} This aural warning has the lowest priority, and is overridden by a warning of higher priority, such as from the EGPWS,{{cite web | work = Airbus Safety First #03 December 2006 p. 5/5 | series = Airbus Safety First Magazine | title = Dual Side Stick Inputs | date = 2024-11-23 | url = https://safetyfirst.airbus.com/app/themes/mh_newsdesk/documents/archives/dual-side-stick-inputs.pdf | quote = "Note: This audio has the lowest priority among the synthetic voice audio alerts."}} posing a potential risk. Examples of this occurring include the 2009 crash of Air France Flight 447 (an Airbus A330 flying from Rio de Janeiro to Paris), the 2010 crash of Afriqiyah Airways Flight 771 an Airbus A330 from flying Johannesburg to Tripoli and the 2014 crash of Indonesia AirAsia Flight 8501 (an Airbus A320 flying from Surabaya to Singapore)..

Comparison of passive and active side-sticks

Passive side-sticks

In the centre stick design, like traditional airplane 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 .

Active side-sticks

However a later, significant, development is the "active" side-stick, used in the Gulfstream 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 to the pilot during manual flight. In 2015, the three largest avionics manufacturersHoneywell, Rockwell Collins and Thaleswere predicting this would become the standard for all new fly-by-wire aircraft. In 2015, Ratier-Figeac, a subsidiary of UTC Aerospace Systems and supplier of passive side-sticks to Airbus since the 1980s, became the supplier of active side-sticks for the Irkut MC-21. This is the first airliner to use them.

Such an active side-stick can also be used to increase adherence to a safe flight envelope by applying force 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 their situational awareness.

References

References

1. Crane, Dale: ''Dictionary of Aeronautical Terms, third edition'', page 463. Aviation Supplies & Academics, 1997. {{ISBN. 1-56027-287-2
2. "Fly-by-wire - A CIVIL AVIATION FIRST". [[Airbus]].
3. Ranter, Harro. "ASN Aircraft accident Airbus A330-202 5A-ONG Tripoli International Airport (TIP)".
4. Page 81 "Conclusions" [https://reports.aviation-safety.net/2010/20100512-0_A332_5A-ONG.pdf Final Report of AFRIQIYAH Airways Aircraft, Airbus A330-202, 5A-ONG Crash], Occurred at Tripoli (LIBYA)on 12/05/2010 Published February 2013.
5. (2009-06-12). "Is Flight 447's 'Fly-by-Wire' Aircraft Technology Safe?". Fox News.
6. Ross, Nick. (2012-04-28). "Air France Flight 447: 'Damn it, we're going to crash'". [[The Daily Telegraph]].
7. "Commercial Active Sticks - An Active Role".
8. "BAE Brochure".
9. Dubois, Thierry. (29 June 2015). "Cockpits of the Future". Skies magazine.
10. https://www.youtube.com/watch?v=3sXXx8rgeeE, How Collins Active Control Sidesticks Work – Aviation International News Aug 13, 2019
11. https://www.flightglobal.com/mc-21-ushers-active-sidesticks-into-commercial-aircraft-cockpits/116609.article MC-21 ushers active sidesticks into commercial aircraft cockpits By Stephen Trimble 22 April 2015.
12. (2015). "Tactile Feedback and Situation Awareness-Improving Adherence to an Envelope in Sidestick-Controlled Fly-by-Wire Aircrafts.[sic]". 15th AIAA Aviation Technology, Integration, and Operations Conference.