The word 'Fidelity' is derive from the Latin word fid─ôlis (A III adjective), meaning "faithful or loyal". This perfectly describes one of the premiere requirements for a simulator where the words "faithful' and "loyal" pertain to the accuracy of the machine. Most of us think of a simulator as a machine that must do many things. The facts are quite different from this belief. A simulator has to do one thing only and it has to do it well. To make the person operating it believe that they are somewhere else or in another place and time. This mind manipulation process is called "suspension of disbelief". Suspension of disbelief is a phenomenon where the occupant (usually the pilot) stops thinking he/she is in concrete building in some suburb and starts believing that he/she is in a real flying aircraft somewhere over Europe or elsewhere. The depth to which this belief intensifies to is known as immersion. It could be likened to a type of hypnotic effect.
In simple terms a simulator is a box with a flightdeck built inside it. Once seated inside that flightdeck, there can be no clues to destroy the illusion that this is not an aircraft. Simulators are high in detail with nothing being overlooked. Every switch, knob and lever must look and feel the same as the ones in the real aircraft. Every label and rivet must be placed exactly as the aircraft it is simulating right down to the registration placard. Ergonomically the simulator must feel the same as the aircraft. On high level simulators, manufacturers go to great lengths to set the flightdeck up exactly the same as the original flightdeck. Experienced pilots are notoriously picky when it comes to detecting differences between a simulator and the real aircraft. If a pilot cant be convinced that the simulator is a close representation of a real aircraft, then the battle for immersion is lost. Pilots generally don't like simulators and will try to find any excuse to show up the simulator as being inadequate. This is not because pilots are generally arrogant, but because a simulator is usually a test and affront to their finely tuned senses and cognition skills. Besides that a simulator is often seen as a hi-tech torture chamber for pilots. Keep in mind that pilots like to fly and not practice things that probably wont happen.

The issue of fidelity is one of the driving forces that will make you spend way more money than you ever budgeted for.
While you may be content with certain compromises in the short term, your growing desire for fidelity perfection will make you push the boundaries of your financial ability to produce the perfect simulator.

The value of simulator practice
To demonstrate the value of simulator rehearsal just remember that incident when a BA Airliner en-route from Jakarta(Indonesia) to Perth(Australia) ran into a volcano dust cloud that turned a fully functioning B747 into a 300 ton glider after the dust cloud shut down all 4 engines. After the flight crew restarted the engines and returned the aircraft to normal operations narrowly avoiding a sea ditching. They were asked how they felt at the time and how they diagnosed the problem. In true British, stiff upper lip fashion the FO replied "it was nothing really, we just followed simulator procedure and got the whole show going again".

Control loading 
Often incorrectly called “force feedback”
What would you consider to be more important on a simulator; a motion system or a control loading system? Control loading is the simulation of flying forces generated by a variety of systems on the simulator. Control loading is considered to be one of the primary systems on the simulator, more so than a motion system. Why?
A pilot feels everything that his aircraft is doing through his control column, yoke or side-stick. Virtual forces acting on the virtual aircraft are transmitted through the control device to let the pilot understand such things as the aircraft trim and speed.

How do they work?
Control uses several key elements to simulate flying forces on an aircraft.To detect what the pilot is trying to do, it uses a load cell that proportionally measures which direction and velocity the user is trying to move the control and how much force they are using to do that. The forces acting on the load cell are sent to a computer running a control loading program. This program is hugely complex as it computes data such as flying speed, ambient air temperature, the surface area of the control. Some complex algorithms even take into account where the control is actually hinged and what type of static balancing is used. This data is usually computed at no less that 60hz. Once a result is obtained, the computer then commands the force actuator to move the control to x position. X position may be a new position or it may be to maintain the current position and not let any force move it. As previously mentioned, this all happens at about 60 times per second and is totally unnoticeable to the pilot. 
Contrary to popular understanding control loading uses a command-result paradigm and not a "I want to move the controls here, try and stop me" system. In simpler terms it means that the pilot requests a new control position and the control loading responds proportionally. For example, if the pilot pulls back on the control column using x amount of pressure, then the control loading's logic system moves the control to the new position if calculations allow the movement to be allowed. The force algorithm may calculate that the pilot needs to input x kilograms to move a control to a new position. This way of doing things mimics real life and the control systems on an aircraft. On a simulator, when you encounter an out of trim situation, the actuating device on the control loader will attempt to move the column to a new position, thus altering the pitch angle. If you attempt to fight this movement with out altering the pitch trim, then the control loading mechanism will continue to resist your forces. Although you can often overpower the control loading system temporarily, its persistence and continuous brute force will eventually have its way and you will weaken and relax your attempts to maintain a fixed control position.

Electric or Hydraulic?
There are two systems used to generate control loading in a simulator. The hydraulic control loading system consists of a load cell that is fitted in between a hydraulic piston and the control in question. Hydraulic pressure is fed to the actuator to move or maintain the piston's position. Pressure to the hydraulic actuator is controlled by a servo valve. Hydraulic control loading is an old and less desirable system on modern flight simulators giving way to the newer, more reliable and less complex electric systems. Electric control loading uses a very powerful DC motor to move or maintain a control position.The DC motors used are called static torque motors and are like the same motors used in those force feedback joysticks most of us own.They do not require any of the undesirable elements that hydraulic systems do such as oil, three phase power,a large noisy oil pump. The whole unit is installed directly on the simulator.

Passive Control Loading
For the non professional or Amateur constructor the Passive systems is probably the best and affordable option unless your surname is either Gates or Hilton. Passive control systems require no electronics or complex machinery to make a really basic system can be put together for as little as $200.
A basic passive control loading system consists of gas dampers mounted in such a way that they resist the rapid movement of any control axis in the same way that the gas dampers on your car hood resists the panel slamming shut. You can even get adjustable dampers that allow you to adjust how rapidly the piston in the damper can move in and out.
The advantage of the passive system is that it is;
  • very affordable
  • easy to set up.
  • makes controls feel infinitely more realistc.
  • requires no complex electronics.
  • doesnt need maintenance.

The disadvantage to a passive system is that it;
  • pressure does not change with airspeed or trim value.
  • wont feel realistic to experienced aviators
  • provides no usable feedback.

Essentially, a passive system is much, much better than nothing, but while it wont pass scrutiny by those who have flown an airliner, it is the first step to designing a system that is impressive and truly usable. Once you start to work on making a basic passive system reactive to trim and airspeed, you may end up with a really decent home built control loading system.

Breakout is a little known aspect of control loading. It is the forces required to move the control column from a stationary state during test. Breakout is a test of the control loading's sensitivity to force.It is a test of the control loadings ability to detect small forces and a test of its ultimate sensitivity.

What simulator controls have control loading?
In a level D simulator, the following items usually have control loading.
• Roll, Pitch,Yaw
• Brakes
• Thrust levers
• Landing gear lever
• Emergency gear release
Although some of these controls use a simplified version of control loading such as spring loading, they do however have to accurately replicate the forces expected on them during normal and abnormal flight.

When good control loading turns bad
A good control loading system is a finely tuned thing that provides the pilot with almost infinite sensitivity and range from fingertip control to bone jarring stick shaker action. If the relationship between computer, load cell and actuator is not in perfect sync, then the control loading system can experience 'neutral stability runaway'. This is a phenomenon where the control loading attempts to stabilise itself in a position, but overshoots. In an attempt to rectify the overshoot, it rapidly applies opposite force and overshoots the position again. This situation rapidly escalates to the point where if the control loading is not powered down or put out of action it will slam back and forth until it destroys itself and/or part of the flightdeck. Sim engineers have found themselves trapped in a seat with the control column bashing back and forth. Exiting the seat is not an option unless you want to run the risk of loosing part of your contribution to the gene pool.

Order of importance.
If you have ever asked yourself what is more important; control loading or a motion system.Consider this;A control loading system will tell you infinitely more about what your simulated aircraft is doing than a motion system.The FAA did some research to discover what system was more important and discovered that motion systems do not make pilots better pilots. On a fully certified level D simulator, you can turn off the motion system and after a few minutes, your mind will adjust and attempt to simulate motion (yes, this is a fact). If you eliminate or turn off the control loading system, the pilot essentially looses all feel and feedback from the airplane. A good control loading system will give the pilot lots of feedback about the air in which he is flying including aircraft trim.A motion system does very little of this.
Got a spare million laying around? For this bargain price, you can own a modern, state of the art, collimated visual system for your simulator. Before understanding the basics of visual systems, you need to be familiar with its acronyms and terms; Image Generators(IG) One of the great things about PC or Mac based flight simulators is that image generation is done within the simulation program with very little help from outside hardware. On an industrial strength simulator there are usually 2 to 4 projectors projecting a range of view angles that make up the complete field of view. It would be quite unrealistic to expect a single computer to be able to output and synchronise all of the visual data needed to display a full, hi fidelity 180 degree system. As you would be aware, a simulator really useful display can be 1.5 metres high by 3 metres wide on any channel, so the likelihood of pixellation and artefacts occurring is greatly heightened. An IG has to move lots of pixels around and do it quickly and smoothly. The volume of pixel manipulation a high end IG unit has to perform is in the order of terra-pixels per second. This requires massive computing power just too great for a single 'do it all' PC to achieve. Higher end simulators usually up to 4 IG units dedicated to displaying a single channel across the simulators field of view.

Most modern visual systems use DLP,CRT or LCD projectors to display the real world just outside of the flightdeck. Even the projectors have varying technologies that render varying advantages to the simulator;
CRT (cathode ray tube)
For a long time CRT has the standard in simulation projection. It rendered the blackest blacks and bright, accurate colours and was an extremely intense projection source. Unfortunately CRT projectors suffer several failings that have ultimately lead to their popularity in use.
Place a magnet near any CRT TV and you will see the effects of magnetism on the display in the form of shifting and wild colours. The CRT projector also suffered the effects of the earth's magnetic field and had to employ sophisticated electronics to compensate for even minor effects such as the change in position caused by the motion system. CRT projectors had a limited lifespan and needed to be replaced at regular intervals.CRT projectors used 3 guns to create an image on the visual system's screen.
LCD (liquid crystal display)
Powered by the evolution of domestic LCD projectors, these units have become, not only quite suitable for low end simulation, but very affordable. Initially LCD projectors had terrible light output and contrast ratios. Blacks were more like very dark greys and images looked flat and depthless. Modern LCD projectors are the most affordable selection for a low cost visual system with a reasonable, single channel solution costing under $1,000. Be warned that like inkjet printers, consumables for an LCD projector may cost more than the initial outlay for the projector. Some years ago, we purchased a bargain projector for a project. Its cost was $900. The lamp gave up after only 2,000 hours. A replacement lamp was $1,200, so we purchased a new model projector for only $820. Cheaper LCDs can be noisy due to the fan required to drag away heat. With continuous use cheaper LCD projectors can suffer from filter burn in which is characterised by a green patch on the projected area. this green patch will slowly get larger as the filter deteriorates and will reduce the effectiveness of the lamps output. 

DLP (digital light processing)
DLP is an entirely different technology to CRT and LCD. It is a complex system that produces high output and very high contrast ratios. In the past its high price tag ensured that it would not be used in lower end simulation.
When it was first released, the average DLP projector cost about $30,000. They can now be had for as little as $500.

Edge blending
When 2 projection channels are butted up next to each other, there is an overlap region between the two channels. To cover up the murky line that would normally exist. Edge blending dissolves the edge of one channel into the other producing a seamless continuous field of view. This means that if you have a 3 channel display, there is an un-broken field of view from left to right. In the edge blending process colour, tint, contrast and brightness are blended electronically and programatically by custom edge blending software. In the early days of edge blending, the joining point of 2 adjacent channels was quite obvious. Modern edge blending software renders the channel joins as almost invisible and not obvious to the pilot.

Calligraphic lightpoints
On older display systems, the FAA required that certain lighting being displayed needed to be intensified by the use of calligraphic projectors. That certain lighting was usually approach and high intensity runway lighting. A calligraphic projector would have the single task of overlaying high intensity lighting on an image to produce calligraphic light-points. With the advent of higher powered, higher contrast and higher output projectors, this extra expense on the development of the modern flight simulator has all but diminished.

Collimation is the process of straightening light rays and preventing their convergence. When these light rays are viewed head on they produce an effect that fools the human mind into thinking that a projected object is many feet or kilometres away. Collimation is the key to the simulator visual system. 2 pilots may be sitting in a simulator looking at the end of the runway which may appear to be several miles away, but the truth is very different from this illusion as the display images they are looking at are usually only several metres away from their viewing positions.

VFOV stands for Vertical field of view while HFOV stands for Horizontal field of view. HFOV is the angle a pilot can view when looking left to right. VFOV is how much of the world vertically the pilot can see.Most modern visual systems can display 45 degrees VFOV, but this is often restricted by the aircraft structure. Most modern visual systems can display at least 180 degrees of HFOV which is enough for a pilot to look left to right and see what they would normally see of the outside world while seated in the flying position.

DEP stands for design eye point, and represents the best position to view a visual system. Without a thorough understanding of visual systems it is hard to understand the importance of this aspect of visual system design. In early monitor based visual systems, head placement was so critical that if a pilot moved his/her more than a few inches the display would loose collimation and the pilot would start to see the edges of the curved mirror and support structure. Modern WAC systems are far less critical in pilot positioning and the even the instructor or observer sitting several metres back can still view effective collimation.

Differing Technologies
The two most used visual system technologies use in high end simulators are the monitor based visuals and the WAC or wide angle collimated system. WAC systems are recognised by the huge dome at the front of the simulator. This dome houses a huge Mylar mirror that is held in place by a vacuum. The visual data is projected onto a semi opaque, back projection screen which in turn reflects onto the large mylar mirror. Collimation is produced by a set of optic laws that allow the pilots to see their environment at infinity.
Now mostly a thing of the past, the monitor based visual system formed the basis for all high end visual systems. The system comprised of a high intensity monitor projecting its output onto a beamsplitter set at 45 degrees to a curved mirror. While the last sentence can hardly describe the workings of the monitor based visual system, it should be noted that this system had several failings and was eventually phased out in favour of the WAC system. One of the facts that caused to monitor based system to be phased out was that one vital aspect of the systems operation was not being manufactured any more. The monitor based system relied on a high output monitor as its visual source. due to the laws of collimation the surface of the monitor must have a radius of 50% of the main collimating mirror. This means that if the main collimating mirror has an effective radius of 3 metres, then the monitor must also have a corresponding radius of 1.5 metres. These monitors and their highly curved screens went out of production back in the early 80's and as a result of spare parts depletion, this type of visual system slowly went out of use and was replaced with the WAC system which had quite a few advantages over it.

What should I use?
CRT projectors are all but gone for domestic use. This just leaves LCD and DLP. LCD is cheap, but does have its problems. DLP is the pick of the bunch as it has superior, output, image and contrast. luckily its cost has reduced dramatically over the last 5 years although it is still generally more expensive than LCD. When choosing between brands look closely at image quality. Like modern Digital SLRs, much of the image comes down to the optics. Since there is a good chance that you may want to butt up 2 images to produce a nice wide display area, you really need to start out with 2 clean edges to butt up next to each other.Some brands may dazzle you with clean bright images, but will have horrible, distorted edges. Another aspect to consider is image correction. Most brands have keystone correction, but others can have pincushion, zoom and other correction electronics.

As with any simulator (including something you have constructed), there are a bunch of devices communicating with the host program and other devices. Think of the simulator as a whole as being just like an intranet. Each panel or device with communication abilities acts like a network node just the same way as all of the computers on an intranet do. In a simulator all of the devices are identified by a unique name or IP address. These devices are always 'listening' to the network to see if they are being sent messages. To understand this in simpler terms read this example. The IOS operator triggers a low fuel pressure malfunction to test pilots reaction. The IOS software immediately writes "ATT:Low fuel pressure Eng 1" to the network. In that instant every device listening to the network is now aware that there is a new message on the network. The message is usually not literal, but is expressed as codes that equates to the message. "ATT:Low fuel pressure Eng 1" may actually be transmitted as "##90642", where '##' means ATTENTION or wake up!!. 90642 may be the equivalent of Low fuel pressure Eng 1. On a properly designed system, the device issuing the command does not address the device it wants to send the message to, but rather relies on the device knowing that it is responsible for handling the alert. The software/ hardware process should work like this; The Master caution system is alerted by the ## or ATTENTION data appearing on the network and prepares to capture the next 5 bytes of data. The master caution system captures the next 5 bytes of data, decodes it and sees that it equates to 90642.  Using an internal lookup table MCS sees it is responsible for actioning this code. According to the MCS internal look up table, code 90642 means raise a visual alert and it correspondingly illuminates the captains 'Fuel' annunciator on the glareshield 6 pack. If 90642 is not in the MCS as a relevant lookup code then the MCS will ignore the code and do nothing. At the same time the fuel panel is also processing the new network data in much the same way and illuminates the appropriate annunciator on the fuel panel. The EICAS does exactly the same thing except it displays red text saying "Alert- Low fuel pressure Engine #1' This of course happens in less than the blink of an eye. Using this system, every device is made aware of a command or alert. whether the device acts upon the alert all depends on the modelled behaviour of the device. The other way that most first time simulator programmers do it is like this; The IOS operator triggers a low fuel pressure malfunction to test pilots reaction. The IOS software immediately writes "Master Caution System:Low fuel pressure Eng 1" to the network. The IOS software then writes "Fuel Panel:Low Fuel pressure Eng 1" Form this point it is the responsibility of the addressed device to process the action. The network technology used by our computers is called Ethernet. In an aircraft the networking system is called ARINC. Arinc comes in many versions and flavours with the most popular being Arinc 429. Although Arinc 429 is not native to the PC, adaptors can be purchased that will convert Ethernet to Arinc protocol. As previously discussed aircraft and simulators make all status and critical information including warnings available on the network to all devices 

Motion in a simulator is a complex task requiring precise co-ordination between a plethora of devices to create the sensation of flight motion in a simulator which is in fact, fixed to the earth. 

Motion cues The most popular form of motion has 6 degrees of freedom and is usually called a 6DOF. Those 6 degrees are; Acceleration. Deceleration. pitch. Roll. Heave. yaw. Acceleration This is achieved by retracting the rear jacks so that the simulator sits back on its haunches. The occupants are pressed back in their seats, thus creating the sensation of almost 1g of acceleration. Deceleration Deceleration is just the reverse of acceleration and is created by tilting the occupants forward so that their bodyweight strains against their harness. Pitch Pitch is usually associated with acceleration and deceleration, but is more subtle and produces a distinct sensation of either tilting forward or backward. Roll Jacks on the left or right side of the simulator extend to create the sensation of a roll. For a more dramatic roll, jacks on the opposite of the extending side can retract to deepen the roll and heighten the roll sensation.  Heave This is one of the most dramatic motion cues with all 6 jacks rapidly extending to thrust the simulator vertically Creating the illusion  Since the occupants of the simulator are visually isolated from what position or action the motion system is actually performing, the only positioning cue is via the visual system. If the visual system displays the horizon dropping away at V2 and this is coupled with a heave cue, then the simulator occupants receive strong visual and motion stimuli that the aircraft is actually taking off. Sustaining the cue Typically motion systems have jacks that are 36 or 42 inches long, obviously it would be impossible to sustain a motion cue exceeding the length of the motion system jack. The motion system coupled with the visual system provides the "onset cue", which is the information the body and brain need to believe that the simulator is performing some kind of manoeuvre. The visual sustains this visual information, making the occupants believe that the manoeuvre is ongoing far beyond the point where the motion system has stopped providing actual motion.  Stewart platforms Named after its inventor, the Stewart platform is also known as a hexapod platform. Whatever the name, a motion system platform comprises of 6 hydraulic or electric "jacks" (see definition below) attached to a platform where the simulator cabin is located. The movement up and down of the jacks is known as excursions, thus a 42 inch hydraulic jack has a 42 inch excursion. Metering of jack position is accomplished by the use of linear measuring devices which are similar to huge slider pots. Another type of metering device works not unlike a tape measure which extends and retracts along with the movement and position of the jack. This linear position is fed back to the host computer to provide feedback as to the position of each jack.  Washout Washout is an operation performed by the jacks on a motion system to provide a means of readiness for the next motion cue. If a jack has extend to its full length of say 36 inches then it is quite impossible to extend any further and perform another motion cue because it simply has run out of physical length. To combat this, the motion platform is programmed to "washout" in readiness for another motion cue. This involves the jacks slowly returning to a halfway point or a fully retracted point in their excursion limit. This operation is performed slowly and subtly, so that the simulator occupants are not made aware of the motion. Washout is also a pre-emptive action that relies on very particular programming to ensure that the motion system is in readiness for the next demanding motion cue.  Hydraulic systems Hydraulic systems are the oldest of motion systems with some designs dating back to the late 40's. They comprise of hydraulic rams or jacks to provide movement of the motion platform. Each jack is powered by a huge hydraulic pump that feeds an array of 6 jacks. Pressurised hydraulic fluid is constantly fed into large cylinders called accumulators. From the accumulators fluid is fed to computer controlled servo valves that regulate how quickly and what direction the jacks more in. The servo valves are the heart of the jacks operation since they are capable of providing minute control over their operation. These jacks are so precise that they can even provide rumble and pavement texture to the simulator platform.Hydraulic systems are slowly being phased out because they are high maintenance, require a lot of infrastructure and are messy due to the use of hydraulic fluids.  Electric systems Pioneered by FCS, Electric systems are slowly taking over from the older, more maintenance intensive hydraulic systems. Electric systems work just like linear actuators that you can easily purchase, except each one is about 8 foot (2.5m)long. They have the ability to extend and retract rapidly in near silence.Electric motion systems have the advantage of requiring very little infrastructure to operate since no large pump room is required. Most older hydraulic systems have metal drip trays positioned under the simulator to catch the constant leaks and drips coming from the system, since electric systems dont use oil or hydraulic fluids, leaks are not an issue.The disadvantage of electric systems is that they do not have a load capacity as large as their hydraulic counterparts. One final note A lot more can be said regarding motion systems and while they are impressive and add a lot of realism to a simulator, they may be due for extinction. In a recent FAA study, it was shown that motion systems do not make for a better pilot and the question was raised as to why they should continue to form such a huge part of a simulators expense. If you want to incorporate the elements of fidelity into a simulator, then control loading should be a high priority rather than motion.

Human hearing is one of our most acute senses. We are able to discern sound source direction in minute fractions of degrees due to the brain's ability to measure the timing difference between delivery of sounds between the two ears. This was clearly demonstrated by the advent of stereo encoding in domestic hi-fi equipment which took music from a flat wall of sound to a spatial, precise medium with real depth and clarity. It also took full advantage of the humans brain and its ability to process audio. A simulator must have the ability to make us believe that we are hearing an aircraft operating in an environment. Not only is it required to reproduce wind and weather noises, but it is also required to accurately produce accurate aircraft operational sounds.

Engine noises
If you have ever looked at the sound files of a program such as MSFS, you will see that there is no singular engine sound file. To its credit this program actually combines 3 engine noises to create the engine noises. The sound of an engine comprises mainly of 3 noise sources;N1,N2 and the exhaust section. These are recorded separately and electronically blended to product a true turbine engine sound. This technique also allows for differing noises when the aircraft is observed from different locations. On the flightdeck with the cabin door shut the sound of the engines starting or spooling up is very different from what is heard in the cabin or from your passenger seat. When seated in your comfy chair with an inflight magazine in front of you, the sound of the starting engines is quite obvious whereas on the flightdeck the engines starting can be barely heard.The fact that anything at all is happening is only apparent by the rising engine RPM and EGT indications. Having said this, what is heard on the flightdeck can alter greatly when the aircraft is in proximity to buildings and other aircraft.Engine sounds should be processed before being reproduced for the flightdeck. A 5.1 sound system is a great way of creating the illusion that the engines are 40 or 50 foot aft of your position. Speakers should also be placed behind and centre of the pilots position.

The fact that wind is coming head on from the flying position indicates that speakers reproducing wind noise should be placed in proximity of the windshield . Since it is not practical to have 2 large speakers positioned on the windshield, the next most practical place is in the pilots footwell. On commercial speakers are often placed outside near the windshield and near the DV windows. Wind noise is usually modulated Brown noise and is produced from looped samples of Brown noise.

Thunder is sampled from real thunder and is reproduced by a subwoofer mounted on or near the flightdeck shell. Because thunder can occur either close or many miles from the flying aircraft its intensity can vary greatly. The white noise produced by the wind of the flying aircraft can greatly obscure and attenuate the sound pressure wave produced by thunder. For this reason, reproduction of thunder is treated with great care. For people setting up simulator audio systems, there is the tendency to make thunder too loud or boomy. This is not how it sounds in reality. Thunder should be subtle yet audible with its lower frequencies being obvious yet not overbearing.

A malfunction such as an engine failure or tyre burst is not a huge or deafening event. You can certainly tell that something has gone wrong usually by the screaming warnings on the flightdeck, but other than that there is usually no other warnings except for a thump and an aircraft that now handles like a bag of S***.Keep in mind when designing malfunction sounds, that between the pilot and that blown CFM-56 engine there is a huge amount of aircraft structure and insulating material to cushion and attenuate the sound. This tends to make sounds dull an muffled. As an example of the attenuation, look at UAL flight 232 which was a DC-10 that lost its centre engine fan disk near Sioux City, USA. This massive explosion of the engine caused catastrophic failure of not only the engine, but also the controls hydraulic system, yet on the flightdeck al, that was heard was a muffled 'thump' followed by the usual flightdeck warnings and alerts.

Sound design on a simulator flightdeck should not be treated as an afterthought and is every bit as important as the hardware that makes the simulator work. Keeping speakers out of sight yet very functional is harder than it looks. Sound depth perception and fidelity play a huge part in convincing pilots that they are hearing actual flying sounds.
This is an often overlooked and mis-calculated aspect of simulation and is responsible for most simulator fidelity failures. In essence, latency is a time delay caused by the components of a system. Those components can be software, network, hardware. Latency is often hard to pinpoint and track down in a simulator system as the slow component may not be obvious. A good example of latency can often be found in amateur concoctions of the MCP (mode control panel). When the rotary encoders for a particular display were cranked rapidly, the display would show obvious lag and take time to catch up to the positioning of the encoder. The reason for this type of latency can be discovered by following the logical steps used to alter the display indications.

(1) once the encoder knob was turned, signals were sent through the network to the MCP encoding logic.
(2) poorly written logic interpreted the pulses from the encoder and determined the direction and positioning of the encoder.
(3)The MCP program sends updated display information to the MCP display over the network.
(4)The display logic receives the new display settings over the network and updates accordingly.

By looking at this breakdown in how early logical systems worked it is plain to see how many things can go wrong and cause delays in an action being carried out. In Most modern systems, the logic and network are integral to the actual device using embedded computing. A dedicated program may look at only controlling a display by monitoring an input device such as a rotary encoder.

Latency is usually measured in milliseconds MS or thousands of a second. On higher level simulators latency is set to tolerances of 300 or 150ms which means that updates and changes have to occur at high speeds with delays being only 150 thousands of a second. Any higher cannot be tolerated.

Vomit comet
Latency can have particularly undesirable consequences when introduced into a motion or visual system. The synchronisation between sight and movement must be strictly adhered to. If visuals and motion become un-synchronised during manoeuvres due to latency then the occupants will become rapidly nauseous due to the mis-coordination between sight and motion sensing in humans. This is a phenomenon produced by the inner ear's balance mechanism