Given that most modern aircraft are controlled using the fly by wire system, what is the likelihood or the drawbacks of transmitting those fly by wire instructions from the cockpit and or cockpit computer wirelessly? Wires add weight to the aircraft and hence increase the net fuel burn. I'm assuming a totally wireless system is not already in use today.
The fly-by-wire is absolutely vital for control of the aircraft, and the three dominating factors here are safety, safety and safety. Weight is not one of them. The fly-by-wire system is triple or quad redundant: instead of removing a set of cables, the manufacturers are installing 3 more cable looms, just to make sure that the system always works.
Wires are safer than wireless!. There are active transmitters and receivers in wireless systems, which can fail. Signal reception depends on the quality of the space between transmitter & receiver: can the signal always penetrate the aluminium bulkhead? What happens to the wireless signal when flying past airport radar or in the weather radar field of another aircraft?
Shielded wires are passive and relatively immune to electro-magnetic radiation, and are the means of choice for such a safety critical system.
The OP was on fly-by-wire. In a sense, the flight control system is the most safety critical system on board and must be immediately available at all times. The presentation linked to by @mins in a comment reports on the progress of on-board wireless communication, for systems with a less critical safety aspect:
Examples of Potential WAIC Applications
Low Data Rate, Interior Applications (LI):
- Sensors: Cabin Pressure - Smoke Detection - Fuel Tank/Line – Proximity Temperature - EMI Incident Detection - Structural Health Monitoring - Humidity/Corrosion Detection
- Controls: Emergency Lighting - Cabin Functions
Low Data Rate, Outside Applications (LO):
- Sensors: Ice Detection - Landing Gear Position Feedback - Brake Temperature - Tire Pressure - Wheel Speed - Steering Feedback - Flight Controls Position Feedback - Door Sensors Engine Sensors - Structural Sensors
High Data Rate, Interior Applications (HI):
- Sensors: Air Data - Engine Prognostic - Flight Deck/Cabin Crew Images/Video
- Comm.: Avionics Communications Bus - FADEC Aircraft Interface - Flight Deck/Cabin Crew Audio / Video (safety-related)
High Data Rate, Outside Applications (HO):
- Sensors: Structural Health Monitoring
- Controls: Active Vibration Control
From the same presentation: An A380 has 5,700 kg of wires on board, and 30% of them are potential candidates for a wireless substitute. So wireless communication on board of aircraft does make sense, starting with the non-safety critical systems first.
That will be very unlikely simply because wireless is much less reliable by several order of magnitude.
considering the current day an age of terror threats if the encryption (and you will need encryption) is ever compromised this would allow a passenger to hack into the datastream and Man in the Middle the controls for a hijack without ever entering the cockpit.
You also have not considered the power requirement of the wireless communication, that will also increase fuel cost.
To save a few hundred kilograms of weight this is never going to happen.
Although technically feasible, having wireless communication between cockpit and the various end-points around the aircraft produces significant issues.
Channels: Unless you use multiple frequencies, each sensor or driver would need it's own radio channel. Add in redundancy and you need like three channels per sensor or actuator station.
Bandwidth: Wireless communication is limited in how much data you can transfer at a time. Since you would be sharing the channels over multiple devices, this further limits how fast you can communicate with it.
Interferance: Assuming you can even get all these devices working at the same time, you are very susceptible to electrical noise. Whether that be Timmy using his little game-boy, or dad using his electric razor in the washroom, or travelling through an electrical storm, a sudden loss of communications in any form would be detrimental to the passenger and crews flight experience.
Security, Hacking / Blocking: It would be rather too easy for a would be terrorist to turn on a transmitter to block the wifi or hi-jack the control system.
As such, wireless communication would be a rather dangerous road to venture down.
As for harnesses. When it comes to control systems, harnesses can be significantly reduced by using a different method. By using distributed smart controllers located around the aircraft, a single wire communication system can be used to connect them to the main flight computers. That is, you really don't need a wire in a harness for every switch in the cockpit.
As always, there needs to be redundancy here, you design it with two or three communication cables routed through the roof, floor etc. for redundancy in case one fails or is severed. You would still need a power distribution system of course.
However, the issue with all these methods is that of channelling too many functions through a single point. Although it may be a simpler system and more reliable, the consequences of a failure are far more significant.
In my opinion, the most important issue would be that of immunity towards the interference to wireless signals (from the FCS to the actuators) from external sources or impact of environmental factors on the transmission of the signals - what is the reliability of the wireless signal transmission in all the imaginable situations. Until we have a technology which eliminates these issues the industry would be very sceptical of use of wireless FCS. As of today, the next thing coming up in FCS is Fly-by-Light i.e. signal transmission using fibre optics. There are a number of pros of FBL over conventional FBW such as high speed, immunity to EM interference etc, but at the same time it may not be significantly lighters than copper wires as a over-all system which could trigger the switch to FBL in civil domain for example.
While wireless communication could help to reduce the number of cables, the remote control units and remote terminals still require cabling for power.
Advantages of wireless systems include mobility and flexibility. These could be driving factors for some early prototypes, but clearly not for certified airliners. The side effect of harness reduction is not significant.
Thus, doing with less wires is possible, but wireless is not.
There are several pros and cons to the system, and several great links to existing research have been provided by others here. Manufacturers like Gulfstream and Boeing have prototyped some examples of wireless avionics and it's an area of active research with plenty of papers proposing different strategies. So I wouldn't go so far as to say that fly-by-wireless is unworkable or a horrible idea, although it's telling that it hasn't been widely deployed yet in other industries for in-vehicle networks to my knowledge. Like many ideas posted here, it has its merits but the benefits may not be enough to overcome the challenges.
Pros to wireless control:
- Less cabling weight, maybe by as much as over a thousand kilograms
- Reduced engineering cost for harness design, cable routing, and shielding
- No wires that you have to shield from electrical interference (instead you have an antenna picking up interference)
- Fewer issues due to broken connectors, snapped wires, transmission line effects from faulty terminations, etc.
- Increased engineering cost in wireless transmitters
- Increased complexity (think of how Wi-Fi has more connection issues than LAN)
- Greater chance of single-point-of-failure issues. Aircraft have several redundant buses routed through different points in the aircraft. It's easier to jam or take out all wireless communications than all these redundant wires.
- You need to use a secure architecture with encryption and authentication signatures because you no longer have a guarantee that intruders aren't on the data bus. The military already uses similar technology in a variety of radio applications.
- Extra security software and hardware to detect network intruders, prevent dangerous interference, etc.
- Impossible to completely protect from jamming, even if using military-grade anti-jamming techniques like spread spectrum and frequency hopping.
As an interesting point related to hacking, most modern flight control computers are immune to nasty Byzantine General errors. These errors are situations where one of several sensors or control computers fails and misleads the others, including even lying to one and telling the truth to another. Even in these situations, the system is designed to detect the liar and still reach full and correct agreement between the functioning computers. To take down these systems you'd have to impersonate two, or sometimes even three, flight control computers or servos at once.
Also, many systems are designed to prevent hardover. For example, the if the rudder is detected to deflect fully, the avionics might revert to a simpler backup control system (which is possibly mechanical). These systems can be circumvented with the right techniques of course, but to imply that its trivial for one system to go rogue and take down the whole plane is like implying a bridge will fail if you cut one support beam. You shouldn't ignore the extensive safety analysis and redundancy that goes into these designs.
Wires are far more resistant to electromagnetic interference, either intentional or situational, than radio signals.
Also, transmitting radio signals to remote receivers that are encased in either aluminum or carbon fiber would pose some difficulties. One could use the aluminum skin of the aircraft as an antenna, but that would be supplying a great antenna for external radio signals, too, and you have a potential interference issue again, one that could be applied external to the aircraft.
A more practical approach has been to replace metal wires with fiber optics. Fiber optics have a higher speed and much wider bandwidth that can carry multiple signals per strand, as well as weighing a lot less.
Some years ago, the Lockheed C130 was redesigned with a fiber optic based system. The result removed so much wire and weight from the cockpit area that the previously optional cockpit armor became standard, to keep the plane in balance when it had no cargo.
Something I haven't seen any other answer touch on is this: Wireless transmitters require wires to power them. Instead of running a wire from cockpit to system, you're running a wire from the planes power grid to the transmitter, then another wire to the receiver.
Congratulations, by not using wires, you've doubled the number of wires.