## What is wake turbulence?

WHAT IS WAKE TURBULENCE

Why is it necessary for the aircraft to have some minimum separation between each other while they are flying or they are approaching a runway to land? There are many factors which determine the minimum separation required between two aircraft to have a safe flight. The primary reason for the requirement of a minimum separation is to avoid wake turbulence. This article would provide the analysis of wake turbulence formation and its avoidance.

How is wake turbulence created?

Lift is generated through the wings because of the pressure differential between the lower and the upper surface of the wing. Air pressure below the wing is higher than air pressure above the wing, which in turn generates the lift required by the aircraft to fly in the air.

If the behavior of flow at the wingtips is analyzed, it could be observed that the high-pressure air from the lower surface would try to come to the upper surface by following a circular path. This would result in wing tip vortices which would trail behind the wing. While the aircraft is generating lift, at the same time it also results in wingtip vortices.

Factors affecting the intensity of wake turbulence:

The intensity of these vortices is directly dependent upon the magnitude of lift generated by the wing. Therefore the intensity of wingtip vortices varies with angle of attack, weight, and speed of the aircraft. These vortices are strongest when aircraft is heavy, slow and in a clean configuration.

As these vortices are invisible pilots must learn to visualize and avoid them. If a smaller aircraft has to land behind a heavier one, it must always fly above the flight path of the heavier aircraft to avoid the encounter with wake turbulence. It should be ensured that the touchdown point of the aircraft is aft of the aircraft which has previously landed.
Sometimes the wake turbulence created by an aircraft during take-off may travel to another runway due to cross-winds. Therefore the crosswinds must also be analyzed before taking off.

Different wake turbulence weight categories:

Wingtip vortices or wake turbulence has a sink rate (that is the rate at which it comes down) of about 400 feet per minute. These vortices come to rest at about 800 feet below the flight path of the aircraft.

Different aircraft would require different minimum separation, therefore it is necessary to categorize the aircraft based upon their weight. Lightweight category i.e. category L is for aircraft weighing less than 7 tons. Medium weight category is for aircraft weighing between 7 to 136 tons. Aircrafts weighing more than this are categorized as heavy. There is yet another category which used for aircraft with a take-off weight of about 550 tonnes and this category is called super heavy category.

Regulations related to minimum separation:

ICAO (International Civil Aviation organization) regulates the minimum separation between two aircraft. The minimum separation depends upon the weight categories of the aircraft. If a medium weight category aircraft follows a heavy aircraft then there must be a separation of 5 nautical miles. The minimum separation required could even go up to 8 nautical miles if a lightweight category aircraft follows a heavy aircraft.

When a heavy aircraft follows a lightweight category aircraft the minimum separation required is only 4 nautical miles. It is not only the duty of an ATC controller to guide the airliner about the wake turbulence but it is also a duty of the pilot to ensure that the aircraft is flying at a safe distance.

Therefore it could be concluded that wake turbulence is the primary factor determining the minimum gap required between the two aircraft to fly safely. If any aircraft encounters this turbulence then it would roll and could even cause a crash if not controlled properly.

There was a crash caused due to wake turbulence on 12th November 2001. This accident was accounted for the excessive rudder input provided to the American Airlines Flight 587 in response to the wake turbulence caused by Japan Airlines Boeing 747.

A weather radar or a weather surveillance radar (WSR), is installed in aircraft in order to determine certain weather conditions in the atmosphere like, locating precipitation or calculating its motion and even estimate the weather situations like rain, snow, hail etc.
Most of the weather radars installed in aircrafts today can determine the motion of water droplets and also the level of intensity of the rain.

A typical aircraft uses basically three kinds of aids to help determine the weather, which is usually referred to as weather radars. They are categorized into;
1. The on-board radar for detection and displaying the weather conditions.
2. Lightning detectors.
3. A weather radar receiving information from an outside source.

#### How Aircraft weather RADAR works?

These weather radars are present in almost all airborne vehicles regardless of their sizes. The functioning of a weather radar is quite similar to that of an Air Traffic Control system, the only difference being that instead of the radio waves which bounce after intercepting with an aircraft, they bounce back from precipitation. The level of reflection of these radio waves is dependent on the intensity of the precipitation. A display is installed on the flight deck to aid the pilots indicating the level of intensity of precipitation, depicting heavy fall with a red signal, moderate with yellow and light with a green signal. Water vapor or clouds do not contribute in creating these signals. However, in case of turbulence or extreme precipitation which requires additional pilot intervention is depicted using a magenta signal. In order to economize the panel space, in most of the aircraft, the weather radar displays are integrated into the navigation display.

A weather radar typically used radio waves in the SHF range. These radio waves are directed through a non-metallic nose cone in the forward direction by a directional antenna. A constant cycle runs throughout this process and uses a receiver to process a two-dimensional image which is displayed. This process is carried on and facilitated using a control panel.

To increase the versatility of the weather detection system of an aircraft, it is designed with the capability of distinguishing turbulence, wind shear and hail which are some of the major concern to the pilot. The movement patterns help to correlate the wind shear and turbulence while hail provides a return on the weather radar. It is not possible to detect and display dry air turbulence. This is also facilitated using a control panel.

Fact : An aircraft weather radar is also capable of detecting another aircraft in flight. The weather radars are capable of detecting wet hail, rain, and wet snow but not dry now or dry hail. Which proves its ability to detect moisture in the atmosphere and make conclusions accordingly.

#### PRECAUTIONS

There are additional precautions and care that is kept in mind while designing and constructing the weather radar system. For example, specially approved paint is used to cover the radome which covers the antenna so that there is no obstruction for the passage of radio signals.

There are also some instructions that need to be followed to help the pilots retain their performance. As the eyes and testes are very vulnerable to physical harm by the high energy radiation emission. It is also advised to not look directly into the transmitting radar. These radio signals can lead to high interference and cause casualties which is why they are not operated when the aircraft are placed in hangars unless special arrangements are made like signal absorbers in the hangar. It's also preferred to not point these radar signals towards any building or so.

Identification of potentially dangerous weather is made possible using lightning detection. This lightning detection is achieved by studying the electromagnetic signals which are given out by the lightning itself. ADF antennas are most commonly used in lightning detectors.

Suggested article: Endoscopy of the Aircraft!

## Borescopy- The Endoscopy of an Aircraft Engine

At some of the other point in your life, you must have gone through the word endoscopy. In simple words, the endoscopy of an aircraft engine is known as boroscopy. Let us understand this in a more practical way. A person X is walking on the road and unfortunately, he meets an accident. He was immediately taken to the hospital where the doctor after an investigation found that he has got an injury on his left knee. Now what the doctor can see is an external injury from which a small amount of blood is dripping out!

The doctor carries out the first aid procedure of the injured location. Now X tries to stand on his legs again but he feels immense pain in his knee. Is this pain only due to the external injury? Not exactly there may be some internal injury also.  How would the doctor find out what is exactly the matter? The answer that would pop up to your mind is an X-ray test.

Now let us relate this to an aircraft engine, the engine is not producing the thrust as per the standard values, ripping of all the engine components apart and then reassembling just for one problem would take some two-three days. Is this justifiable? In this world SMART activities, this practice is completely against the T.

SMART here means Significant, Measurable, Attainable, Realistic and Time-based.

Here comes our superhero of the night, “BORECOPY”. In simple words, boroscopy is a method of inserting a small camera inside the engine body to get the live image of all the inaccessible components inside the engine on an LCD screen and analyze their actual condition.

Now I think the root cause behind less thrust production can be found out without even opening a single screw.

Basic Components of a Borescope setup

#### 1. Eye Piece or Monitor

This is a simple LCD screen on which the magnified image of the component being viewed is displayed which is termed as a monitor.

An eyepiece is a viewing device in which the magnified image can be seen, the way as it is used in a telescope or a microscope.

#### 2. Optical System

This is a system consisting of various components such as relay lenses, rod lens system, fiber optic setup etc. apart from them, there is one component of this system which of our interest a CMOS camera. This is a small camera lens which is fitted at one end of the rigid/flexible cable which goes inside the engine. This camera is special because it has the capability to produce very consistent images despite its very tiny size.

#### 3. Rigid or Flexible cable

This is the cable connecting the eyepiece/LCD screen to the small CMOS camera. This cable can be rigid or flexible based on the work which has to be carried out using the borescope. A rigid cable would restrict the motion of the CMOS camera in linear directions only while the flexible cable can be bent at any orientation to carry out the required work.

#### 4. Light Source

The most important of all is the light source which will illuminate the area under inspection.

How to operate a Borescope

Though we have talked about the working of a borescope the operational procedure of borescope would help us better understand the working of a borescope.

1. The operator would insert the borescope camera end into the engine through various insertion points which are provided on the engine dedicated for borescope inspection only. Apart from the insertion points the holes provided for inserting the spark plugs are also used for this purpose at an average we have 10-15 borescope insertion points for varying according to the models. The small CMOS camera would produce a magnified image on the eye piece/ lcd monitor of the part under observation.

2. After inserting the camera part of the borescope setup the operator would start getting a magnified image of the part under observation on the LCD screen/ eyepiece provided in the setup.

3. Now the operator can simply use his hand to view the different components inside engine such as the turbine blades, compressor blades, combustion chamber etc. Though various SOP(s) are defined for carrying out the borescope inspection but using the borescope in an art and not science. The operator’s efficiency in using borescope would increase with experience.

Let us take a practical example to strengthen our learning about boroscopy.

Pilot after landing flight ABCD at the IGI terminal 3 complaints to the technical department that he felt a certain jerk in engine 2 on the left wing while he was flying over New York. The concerned person of technical department gives these remarks to his team working on that particular engine. The team starts the borescope inspection and inserted borescope camera though port number 9 and finds that there is twisting damage on the turbine blades, they carry out the inspection through all the ports and find out that the twisting damage is present on all the blades of the compressor section also. They give the same input to the data analytics team and after analyzing the flight data they come to know that there was a certain drop in thrust produced by the same engine when it was flying over New York. Hence the team concludes that the damage may be caused due to some sort of birds hit. So in this way boroscopy works.

As the technology is progressing forward, these days companies use boroscopy to inspect the part before and after a certain test run or an experiment so that the before and after conditions of that component can be used to analyze any testing carried out.

So far we have discussed the use of horoscope in the field of aviation only but it used in some other industries such as:
·        Internal Combustion Engines
·        Pipes
·        Heat exchanger tubes
·        Gearboxes
·        Welds
·        Foreign Object Retrieval
·        Cast Parts
·        Manufactured or machined parts

Before closing this article I would like to tell you about the three basic engine checks which are carried out according to the situation.

1. The emergency inspection- This inspection is carried out in case of some emergency conditions only such a bird hit etc.

2. Routine inspection- This is carried out on a regular basis to keep a check on engine health no matter how good an engine performing it has to undergo a routine check.

3. The full inspection- This is the inspection in which the complete engine is ripped off in pieces to check each and every component.

To conclude boroscopy is not just the part of the first two checks as it is very easily understandable but it is the part of the third inspection also, no matter the engine is ripped into pieces but there are still some inaccessible locations.

Thank You!

Suggested article: How helicopter hover in the air?

## HOW DO HELICOPTERS HOVER

### “Aviation is the proof that given the will , We have the capacity to achieve the impossible”                                                 -Eddie RickenBacker

Photo: SAC Faye Storer/MOD

A few decades ago , if someone would have said that Man can fly , no one would have believed him. But on December 17 , 1903 , the Wright Brothers proved everyone that indeed man can achieved the impossible. After years of technological advancements, man was able to build such aircraft called Helicopters that can takeoff and land vertically on any surface and can also remain stationary in air!

## A Brief History About Helicopters :

 Olden day Helicopter

The world’s first practical helicopter had its first flight on 14th September 20818 at Stratford, Connecticut. It was designed and piloted by the infamous Igor Sikorsky. He was then working with the Vought - Sikorsky Aircraft Division of the United Aircraft Corp. It has 3 blade rotor which had a diameter of 28 foot and a blade speed of 300mph. Today , the Sikorsky Aircraft Corporation is owned by the American aircraft manufacturer giant ”Lockheed Martin”  who acquired them for a whooping \$9 Billion USD. Today , they manufacture over 15 different models of helicopters.

 Hovering

## Helicopter Flight Controls :

 Flight Controls

Helicopters don’t have the same set of controls that of a fixed wing aircraft. A Helicopter has the following as flight controls :
1. Cyclic
2. Collective
3. Throttle
4. Rudder Pedals

#### Cyclic :

A Cyclic is a stick which is used to manage the pitch of the aircraft. It allows the pilot to fly the aircraft in any direction (forward,backward,left,right). The rotor tilts in the same direction the cyclic is moved.

#### Collective :

The collective is a lever which is used to make simultaneous changes to the pitch angle. When the lever is raised, there is an equal increase in pitch angle of all rotor blades. When it is lowered , there is an equal decrease in pitch angle of all rotor blades.

#### Throttle :

The function of throttle is to manage the engine RPM. Unlike the throttle in a fixed wing aircraft , the one in a helicopter is designed to work like a motorcycle throttle. Twisting action to the left increases the RPM and the the right decreases the RPM.

#### Rudder Pedals :

Rudder pedals or “anti-torque pedals” allow the pilots to control the pitch angle of the tail rotor. They are called “anti-torque” because they help to compensate the torque generated due to Newton’s Third Law of Motion.

 Physics behind Hovering

In a fixed wing aircraft, the forward motion of the aircraft creates airflow over the wings, which results in generating lift. In helicopters, the rotating rotor blades itself generate airflow over the blades. But the rotation of the blades causes a torque to act on the helicopter, which is balanced by the tail rotor of the helicopters.

## How Helicopters manage to remain stationary in Air?

 Hovering

The act of remaining stationary in air, on a fixed position is called “Hovering”. It is an extremely difficult maneuver and requires a lot of skill for a pilot to hover a helicopter.. The ability of the helicopter to hover comes from the both the lift component and the thrust component.
To hover, a helicopter must balance out all the forces which are acting against it. For doing this , the helicopter :

• must produce lift perpendicular the rotor planes and which is equal to the force of gravity or weight.
• must produce drag which is opposite to the thrust of the helicopter.

When all the opposing forces are in balance, the helicopter remains stationary in air.
Photo Credits :
1. Wikimedia Commons
2. Kinja
3. Royal Air Force , Ministry of Defence

## HOW DOES TRIM WORK

 How does trim work?

To trim an aircraft is a skill that pilots use to ease flying an aircraft. It helps maintain a constant pressure on the various flight controls , often used to maintain a constant pitch or rudder. It reduces the pilot’s workload significantly which allows them to focus on other tasks such as talking with the ATC, observing traffic around them, etc. Trim also proves to be a lifeline in case of an engine failure because it helps the pilots to fly the airplane with asymmetric thrust. Pilots can trim in any phase of the flight except for landing. Since it helps in maintaining level flight, constant rate of climb/descent or direction without the help of computers, it is popularly known as “Poor Man’s Auto Pilot” .

## Surfaces that can be trimmed :

Elevator Trim : Used to maintain pitch of the aircraft
Rudder Trim : Used to maintain direction of the aircraft
Aileron Trim : Used to maintain bank angle
In most of the light aircraft , you will only find an elevator trim control in the cockpit. Rudder and Aileron trim controls are usually found on larger aircraft and only exist as a permanently deflected surface that needs to be altered by hand during the outside check of an airplane. Trim tabs come under secondary control surfaces

## How does it work ?

Trimming is done by small surfaces usually connected to the trailing edge of the ailerons, rudder and elevator called Trim Tabs. In a Cessna 172, the elevator trim is adjusted by a wheel which is located in the pedestal area. The wheel has a marking which clearly indicates the point where the elevator trim will be in neutral or take-off position. The trim wheel is moved in the same direction as the control column. For instance, if the pilots wants to maintain a pitch up attitude, the wheel is to be moved in the same direction. The trim tab on the surface is set up to mimic the  opposite direction thereby nullifying  the force on the control column. For example, if a pilot were to maintain constant pitch up, he/she would keep persistent pressure on the control column while setting the trim wheel to nullify the force to a point where the pilot is no longer required to apply force to the control column anymore.

## Trim during Takeoff and Landing

 Trim during takeoff and landing

In Light aircraft , Trim is always set to neutral position during takeoff and landing phase. Do you know why?
Since they are the most critical phases of flight , pilots need to have full control of the aircraft.
Imagine during the the Final Approach phase, you have trimmed the aircraft to maintain a pitch down attitude and for some reason you need to “Go Around”. Even if you pull the yoke to climb , the elevator being trimmed restricts this action to a certain degree and may not give you the required pitch up attitude to climb. Hence, during take off and landing, the trim is set to neutral so that pilots can have full movement of the control surfaces.

Picture Credits :
1. Pilot's Handbook of Aeroautical Knowledge
2. Wikimedia Commons

## What is Aircraft holding pattern?

WHAT IS A HOLDING PATTERN?

Imagine that you are on an aircraft and about to reach your destination but suddenly you hear the voice of the pilot saying "because of holding we would be about 15 minutes ahead of schedule". This mainly happens either due to busy runways or if a runway is undergoing snow removal procedure. What does an aircraft do during this time, this question shall be addressed through this article in a systematic procedure.

Action taken by ATC (Air Traffic Controller):

What would happen if a traffic light stops working? It would definitely result in a huge traffic Jam. Similarly, if one of the runways of a busy airport gets contaminated due to heavy snowfall, there would be a Traffic Jam in the sky.  Helicopters could easily stay at the same position but the same is not possible for an aircraft, so how would the aircraft be able to stay in the sky and how would they get the command to do so.

As soon as the ATC recognizes the unavailability of a particular runway, it orders the aircraft to enter a holding pattern to prevent a potential Traffic Jam. After this request from ATC, the aircraft starts to loiter and wait for its turn to land. Holding is the time period during which the aircraft is loitering in mid-air and waiting for its turn to land. The procedure used to assure a safe and orderly flow of traffic into and out of busy terminal is called holding.

The shape of a holding pattern:

There could be many ways to enter a holding pattern but all the holding patterns are designed in a similar fashion. The top view of any holding pattern looks similar to that of a race track, with two parallel and two semi-circular paths. These patterns are designed to maintain the aircraft within a specified space for a specific period of time.

Most of the holding patterns are published on an airway chart or approach and landing chart, but sometimes they are unpublished and specified by the ATC. There are various stationary points which could be considered as a holding fix, which is an essential part of the holding pattern. These stationary points include navigational aids like VOR, NDB, an airway intersection and a GPS waypoint.

Components of a holding pattern:
 Hold Parallel Entry
There are mainly three types of entries possible to a holding pattern; these include teardrop entry, parallel entry and direct entry. To understand about the entry procedure to a holding pattern one should be clear about various components of a holding pattern.

 Hold Teardrop Entry
Holding pattern consists of four components. The fixed end is a 180 degree turn and is started at the holding fix. It is then followed by an outbound leg, outbound end and inbound leg which is again joined to the holding fix. In this way, a holding pattern is constructed which resembles a racing track with outbound and inbound legs parallel to each other.

 Hold Direct Entry

Understanding Missed Approach:

The landing approach is terminated if the pilot determines before the decision height or missed approach point, that the runway is not clearly visible and a safe landing could not be accomplished. In such cases, pilot elaborates the situation to the ATC.

ATC then analysis the situation immediately and describes a remedy plan. ATC would either command the aircraft to loiter and wait for land on a different runway or to move to a nearby airport to land. Therefore in case of a missed approach, aircraft might have to enter a holding pattern to wait for its turn to land on a different runway.

Rules monitoring the motion in a holding pattern:

The inbound leg should be one minute long, and the aircraft should be loitering with the holding speed of 230 knots. If the effects of air are neglected, both inbound and outbound legs should be one minute long.

The pilot has to include wind correction angle and time calculation, to counter to the effects of wind. The type of entry to the holding pattern depends upon the current position of an aircraft. A standard holding pattern consists of rights turns.

To conclude, holding could be visualised as a queue where aircraft is waiting for its turn to land.

Suggested article: How does Airbus A320 fuel system work?

## Airbus A320 Fuel System

### TERMINOLOGIES

Fuel storage: Fuel (Aviation Turbine Fuel or ATF) is stored in tanks within wings/fuselage/empennage.
Engine feed: It is the fuel piping and flows control from tanks to engines.
Fuel transfer: Inter-tank movement of fuel to maintain c.g. balance.
Fuel pressurization: Pressurization of fuel tanks by air/inert gas to facilitate fuel flow from tank to engines.
Fuel gauging: Measurement of fuel remaining in tanks
Venting systems: To expel air from fuel tanks during filling.
Refuel/ Defuel: Refilling / dumping of fuel as required.
In-flight refueling: Refueling of flying aircraft from a flying tanker
Fuel jettison: Dumping of fuel to reduce the mass of aircraft during emergency landing.
Cooling using fuel: Use of ATF itself as a coolant to take away excess heat from hot systems.
Fuel tank inerting: Fill emptied fuel tanks with an inert gas (N2) for long inactive storage of aircraft.

#### FUEL CAPACITY AND FEED SEQUENCING

Total fuel capacity : 42,000 pounds
Wing tank inner cell: 12,200 lbs
Wing tank outer cell: 1,500 lbs
center tank: 14,500 lbs

Sequencing:

(a) The Center Tank
(b) The Inner Tanks
(c) The Outer Tanks

### Working of the Airbus A320 fuel system

 Airbus A320 refueling
The fuel board panel indicates the pilot about the current and past status of fuel during the flight. The FOB indicates the fuel on board in Kgs. Further, the fuel tanks are divided into three categories; two wing tanks and one center tank. The wing tanks are further divided into inner and outer wing tanks summing to a total of five fuel tanks in an A320 aircraft.

Each fuel tank is incorporated with a fuel pump connected through fuel lines and valves extending up to the two engines. The display is also used to indicate the temperatures of the wing tanks that they are exposed to during flight conditions. As the fuel from inner wing fuel tanks is consumed and reaches around 750kgs a transfer occurs and the fuel consumed from the outer wing tanks using gravity. This is done in order to avoid wing futter and wing bending which can result in catastrophic events.

Normally, the two sides of the fuel systems are kept isolated from one another, but, in case of any abnormality, the isolation can be removed to enable the flow of fuel from heavier locations to lighter locations. There are a total of 6 fuel pumps, 2 in each wing tank and 2 in the center tank.

#### FUEL RE-CIRCULATION SYSTEM

A fixed amount fuel supplied to each engine is transferred from the high-pressure fuel lime in that engine, through the IDG heat exchanger (where it absorbs heat), to the fuel return valve, and to the outer fuel tank. This process brings about the IDG cooling when the oil temperature is high or when at low engine power. The fuel re-circulation system moves the warm fuel from the IDG cooling system back to the related wing tank.

#### A Fuel leak may either be detected by

(a) Passenger observation (Fuel spray from engine or wing tip), or
(b) Net Fuel quantity decreases at an abnormal rate, or
(c) A Fuel imbalance, or
(d) A Tank emptying too fast (leak from engine, or a hole in tank), or
(e) A Tank overflowing (due to a pipe rupture in a tank), or
(f) An excessive fuel flow (leak from engine), or
(g) A Fuel smell in cabin

Suggested article: How is an aircraft engine operated by electronics?

## Full Authority Digital Electronic/Engine Control

As the world is moving towards automation, so is the aviation industry. Gone are those days when a pilot used to push and pull mechanical levers with all their might to actuate the various functions on the aircraft. Pratt and Whitney JT8D is a good example of the complete engine being controlled by mechanical linkages.

During the early development of aircraft control systems mechanical linkages were the most common method used by almost all the major aviation manufactures around the globe but as the electronics age kicked in researches were carried around all the globe to use electronics in aircraft controlling system. The first major advancement was the analog electronic control system in which simple electronic signals bearing either of the values 0 or 1 were used, though more efficient than the mechanical control system this system was not was reliable.

After the mechanical and analog electronic engine control systems, came the digital electronic engine control system. In diginal electronic control system electronic signals were used to control the aircraft. Lets take a very simple example to understand this, you want to ask a question in the comment section at the end of this article what would your brain do it will frame the question with help of your eyes by reading the article it means it is collectinv signals from your eyes and then it will direct your hand accordinly to write, so it will send a signal to your hand muscles through your nerves.

Kudos! You got it right EEC being the brain of the aircraft, airlerons being the hands and temprature and pressure sensors being the eyes. Let's understand the working of FADEC in a more technical way.

What is FADEC and how does it works?

As the name suggests FADEC is concerned about some very sophisticated and precise combinations of various electronic devices together. FADEC is a computer system coupled with sensors and actuators which is completely capable of controlling the complete engine by itself.

The most common confusions which blow up the mind of almost all the nerds who read about FADEC, What is EEC? How it is related to FADEC? and many more.....!

Let's get a bit technical

The electronic engine control or the engine control unit is an electronic computer system which performs all the computation in the FADEC system. In simple language if we use EEC alone then the pilot can override the decision taken by the EEC hence manual controlling is available but when the EEC becomes a part of the FADEC system, then decision of EEC cannot be overridden by the pilot making it the supreme controller of the aircraft.

#### Sensors

Sensors in aviation industry are nothing but devices which are used to collect data about various operating conditions of the aircraft such as pressure and temperature at various engine stations. The other types of sensors are the ones which give the information about the exact location of various components of the aircraft such as the control surfaces.

Actuators

Actuators are the devices which are used to control the various components of the aircraft such as the control surfaces, bleed valves etc. For example if the pilot wants increase the angle of attack he would use the torque motor actuator to move the aileron accordingly.

Now you can easily understand the working of a FADEC system, consider an example that the pilot wants to change the angle of rudder by some degrees the FADEC computer would use its sensor to get the exact information about the location of the rudder at that instant and would use various computing operations to analyze the data coming from the sensor as well as given by the pilot and then use its actuator to move the rudder accordingly. You may think that this process is time consuming but it is very quick as the FADCEC computer has the capability of computing at a speed of 70 times per seconds.

The example given here is a simpler one, I am providing an image with the block diagram depicting working of FADEC system.

1.  Power Management Control- Always making the aircraft engine to work at most optimum speeds so that engine works at the most optimum levels i.e. max power in min fuel consumption.

2. Starting Shut down and Ignition Control and the fuel system - The complete starting shut down and ignition of the engine is controlled by the FADEC system after sensing the various thermodynamic and chemical aspects of the air and fuel mixture.

3. Active Clearance Control- The ACC system is also controlled by the FADEC system in which cold bleed air is circulated around the turbine casing so that the expansion of casing due to hot exhaust is compensated.

4. Variable Geometry Control

5. Thrust Reversal Control- Apart from the braking action provided by the flaps, thrust reversing technique is also used for aerodynamic braking. The Thrust Reversal braking is also controlled by the FADEC system.

All in all the prime function of the FADEC system is minimum Fuel consumption minimum Operating costs and minimum Emissions into the environment.

Always stay away from the FOE.

Though FADEC is a fabulous advancement in the field of aviation but every coin has two faces sk let us look at some of the disadvantages of FADEC.