AIR TRAFFIC CONTROL - Your pilot inspects your plane and files a flight plan with the tower. Once the flight plan has been approved, the flight data person gives clearance to your pilot and passes the strip to the ground controller who directs your pilot to push the plane back from the gate. The ground controller him instructions, such as which way to taxi and which runway to go to for takeoff. Once clearance is given, your pilot accelerates the plane down the runway. Your pilot now talks with the departure controller. The departure controller monitors your flight during ascent to the en route portion. Your plane gets passed from sector to sector and center to center. Your pilot then aligns your plane with the runway. When you are 10 miles (16 km) from the runway, the approach controller passes your plane off to the local controller in the airport tower. When the local controller determines that it is safe, he gives your pilot clearance to land.

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Air Traffic Control

How Air Traffic Control Works

BY CRAIG FREUDENRICH, PH.D.

Durin­g peak air travel times in the United States, there are about 5,000 airplanes in the sky every hour.

This translates to approximately 50,000 aircraft operating in our skies each day.

How do these aircraft keep from colliding with each other?

How does air traffic move into and out of an airport or across the country?

The task of ensuring safe operations of commercial and private aircraft falls on air traffic controllers.

They must coordinate the movements of thousands of aircraft, keep them at ­safe distances from each other, direct them during takeoff and landing from airports, direct them around bad weather and ensure that traffic flows smoothly with minimal delays.

When you think about air traffic control, the image of men and women in the tower of an airport probably comes to mind.

However, the air traffic control system is much more complex than that.

In this article, we will examine air traffic control in the United States.

We'll follow a flight from departure to arrival, looking at the various controllers involved, what each one does, the equipment they use and how they are trained.

Airspace and Air Traffic Control

The United States airspace is divided into 21 zones (centers), and each zone is divided into sectors.

Also within each zone are portions of airspace, about 50 miles (80.5 km) in diameter, called TRACON (Terminal Radar Approach CONtrol) airspaces.

Within each TRACON airspace are a number of airports, each of which has its own airspace with a 5-mile (8-km) radius.

The air traffic control system, which is run by the Federal Aviation Administration (FAA), has been designed around these airspace divisions.

The air traffic control system divisions are:

·       Air Traffic Control System Command Center (ATCSCC) - The ATCSCC oversees all air traffic control. It also manages air traffic control within centers where there are problems (bad weather, traffic overloads, inoperative runways).

·       Air route traffic control centers (ARTCC) - There is one ARTCC for each center. Each ARTCC manages traffic within all sectors of its center except for TRACON airspace and local-airport airspace.

·       Terminal radar approach control - TRACONhandles departing and approaching aircraft within its space.

·       Air traffic control tower (ATCT) - An ATCT is located at every airport that has regularly scheduled flights. Towers handle all takeoff, landing, and ground traffic.

·       Flight service station (FSS) - The FSS provides information (weather, route, terrain, flight plan) for private pilots flying into and out of small airports and rural areas. It assists pilots in emergencies and coordinates search-and-rescue operations for missing or overdue aircraft.

The movement of aircraft through the various airspace divisions is much like players moving through a "zone" defense that a basketball or football team might use.

As an aircraft travels through a given airspace division, it is monitored by the one or more air traffic controllers responsible for that division.

The controllers monitor this plane and give instructions to the pilot.

As the plane leaves that airspace division and enters another, the air traffic controller passes it off to the controllers responsible for the new airspace division.

Some pilots of small aircraft fly by vision only (visual flight rules, or VFR).

These pilots are not required by the FAA to file flight plans and, except for FSS and local towers, are not serviced by the mainstream air traffic control system.

Pilots of large commercial flights use instruments to fly (instrument flight rules, or IFR), so they can fly in all sorts of weather.

They must file flight plans and are serviced by the mainstream air traffic control system

Up next, we'll check in with a commercial airline flight before it takes off.

Flight Profile and Preflight

Suppose you are flying across the United States, perhaps from New York to San Francisco.

Your flight, like every other commercial airline flight, follows a typical profile:

1.  Preflight -This portion of the flight starts on the ground and includes flight checks, push-back from the gate and taxi to the runway.

2.  Takeoff - The pilot powers up the aircraft and speeds down the runway.

3.  Departure - The plane lifts off the ground and climbs to a cruising altitude.

4.  En route - The aircraft travels through one or more center airspaces and nears the destination airport.

5.  Descent - The pilot descends and maneuvers the aircraft to the destination airport.

6.  Approach - The pilot aligns the aircraft with the designated landing runway.

7.  Landing - The aircraft lands on the designated runway, taxis to the destination gate and parks at the terminal.

Preflight

While you prepare for your flight by checking your bags and walking to the gate, your pilot inspects your plane and files a flight plan with the tower -- all IFR pilots must file a flight plan at least 30 minutes prior to pushing back from the gate.

Your pilot reviews the weather along the intended route, maps the route and files the plan.

The flight plan includes:

·      Airline name and flight number

·      Type of aircraft and equipment

·      Intended airspeed and cruising altitude

·      Route of flight (departure airport, centers that will be crossed and destination airport)

Your pilot transmits this data to the tower.

In the tower, a controller called a flight data person reviews the weather and flight-plan information and enters the flight plan into the FAA host computer.

The computer generates a flight progress strip that will be passed from controller to controller throughout your flight.

The flight progress strip contains all of the necessary data for tracking your plane during its flight and is constantly updated.

Once the flight plan has been approved, the flight data person gives clearance to your pilot (clearance delivery) and passes the strip to the ground controller in the tower.

The ground controller is responsible for all ground traffic, which includes aircraft taxiing from the gates to takeoff runways and from landing runways to the gates.

When the ground controller determines that it is safe, he or she directs your pilot to push the plane back from the gate (airline personnel operate the tugs that actually push the aircraft back and direct the plane out of the gate area).

As your plane taxis to the runway, the ground controller watches all of the airport's taxiways and uses ground radar to track all of the aircraft (especially useful in bad weather), ensuring that your plane does not cross an active runway or interfere with ground vehicles.

The ground controller talks with your pilot by radio and gives him instructions, such as which way to taxi and which runway to go to for takeoff.

Once your plane reaches the designated takeoff runway, the ground controller passes the strip to the local controller.

The local controller in the tower watches the skies above the airfield and uses surface radar to track aircraft.

He or she is responsible for maintaining safe distances between planes as they take off.

The local controller gives your pilot final clearance for takeoff when it is deemed safe, and provides the new radio frequency for the departure controller.

Once clearance is given, your pilot must decide if it is safe to take off. If it is safe, he accelerates the plane down the runway.

As you leave the ground, the local controller hands your plane off electronically to the departure controller at the TRACON facility that services your departure airport, but still monitors the plane until it is 5 miles from the airport.

Your pilot now talks with the departure controller.

Departure, En Route and Descent

Once your plane takes off, your pilot activates a transponder device inside the aircraft.

The transponder detects incoming radar signals and broadcasts an amplified, encoded radio signal in the direction of the detected radar wave.

The transponder signal provides the controller with your aircraft's flight number, altitude, airspeed and destination.

A blip representing the airplane appears on the controller's radar screen with this information beside it. The controller can now follow your plane.

An airplane's transponder transmits flight data to incoming radar signals.

The departure controller is located in the TRACON facility, which may have several airports within its airspace (50-mile/80-km radius).

He or she uses radar to monitor the aircraft and must maintain safe distances between ascending aircraft.

The departure controller gives instructions to your pilot (heading, speed, rate of ascent) to follow regular ascent corridors through the TRACON airspace.

The departure controller monitors your flight during ascent to the en route portion.

When your plane leaves TRACON airspace, the departure controller passes your plane off to the center controller(ARTCC controller).

Every time your plane gets passed between controllers, an updated flight progress slip gets printed and distributed to the new controller.

En Route and Descent

Once your plane has left TRACON airspace, it enters a sector of the ARTCC airspace, where it is monitored by at least two air traffic controllers.

The radar associate controller receives the flight-plan information anywhere from five to 30 minutes prior to your plane entering that sector.

The associate controller works with the radar controller in charge of that sector.

The radar controller is in charge of all air-to-ground communication, maintains safe separation of aircraft within the sector and coordinates activities with other sectors and/or centers.

The controllers must monitor the airspace at high altitude (above 24,000 ft/7320 m) and low altitude (below 24,000 ft).

The center controllers provide your pilot with updated weather and air-traffic information.

They also give directions to your pilot regarding such aspects as speed and altitude to maintain a safe separation between aircraft within their sector.

They monitor your plane until it leaves their sector. Then they pass it off to another sector's controller.

Another controller, called the radar hand-off controller, assists the radar and associate radar controllers during times of heavy traffic, watching the radar screen and helping to maintain smooth air-traffic flow.

While you are enjoying your meal, snack, in-flight movie or the view outside the window, your plane gets passed from sector to sector and center to center.

In each sector, center controllers radio instructions to the pilots.

The path of your plane may have to be changed from the original flight plan to move around bad weather or avoid a congested sector.

Your pilots may request a change in altitude to avoid or reduce turbulence.

This back and forth between pilots and center controllers continues until you are about 150 miles (241 km) from San Francisco (your destination).

At this point, the center controller directs all planes flying into San Francisco to move from high altitudes to low altitudes and merges the descending aircraft into a single file line toward the airport.

The controller gives instructions to your pilot, such as changes in heading, speed and altitude, to place your plane in line with these other aircraft.

Depending on traffic conditions, the controller may have to place your plane into a holding pattern, which is a standard route around each airport, where you wait until the airport can handle your arrival.

The controller continues to give directions to your pilot until your plane is within TRACON airspace.

Approach and Landing

When your descending plane is 50 miles from the San Francisco airport, it is within TRACON airspace.

An approach controller directs your pilot to adjust the aircraft's heading, speed and altitude to line up and prepare to land along standard approach corridors.

Your pilot then aligns your plane with the runway.

When you are 10 miles (16 km) from the runway, the approach controller passes your plane off to the local controller in the airport tower.

Landing

The local controller in the airport tower checks the runways and the skies above the runways with binoculars and surface radar (local and ground controllers are the only controllers licensed to use visual information in performing their duties).

When the local controller determines that it is safe, he or she gives your pilot clearance to land.

The local controller also updates weather conditions for your pilot and monitors the spacing between your plane and other landing aircraft.

Once you've landed, the local controller directs your plane to an exit taxiway, tells your pilot the new radio frequency for the ground controller and passes your plane off to the ground controller.

The ground controller watches the runways and taxiways and uses ground radar information to ensure that your taxiing aircraft does not cross active runways or interfere with ground vehicles.

He or she directs your plane to the appropriate terminal gate.

Ground personnel from the airline use hand signals to assist your pilot in parking the airplane at the gate.

Careers and Concerns

What does it take to be an air traffic controller?

To be a ground controller, you have to memorize the position of aircraft on the runways and taxiways with a single, short glance.

Local, TRACON and ARTCC controllers must be able to think and visualize in three dimensions.

All controllers must be able to gather information from what they hear, make decisions quickly and know the geography of their own airspace, as well as that of others.

They must be able to read and interpret symbols as well as predict the whereabouts of aircraft from course headings and speeds, and they must be able to concentrate intensely..

Air traffic controllers at all levels are employed by the FAA.

Air traffic control positions are highly competitive jobs, and the controller workforce is relatively young (most were hired after the air traffic controller strike in the 1980's, when President Ronald Reagan ordered that all striking controllers be fired).

Air Traffic Control Problems

Air travel has increased dramatically since the U.S. federal government deregulated the airline industry in the 1970's.

However, the construction of new airposts and runways has not kept pace with the increase in air traffic.

This has put excessive pressure on the air traffic control system to handle the nearly 50,000 flights per day, a number projected to increase in the near future.

To handle these flights and avoid delays and collisions, the FAA and NASA have developed modern software, upgraded existing host computers and voice communications systems and instituted full-scale GPS (global positioning system) capabilities to help air traffic controllers track and communicate with aircraft.

The FAA is currently redesigning U.S. airspace to make more room for increased traffic. For example, the U.S. military has freed previously restricted airspace off the coast of North Carolina for use by commercial aircraft.

These efforts should help ease traffic and minimize delays in the short term; however, increasing airport capacity by building new runways and airports is ultimately the way to handle the problem.

Craig C. Freudenrich, Ph.D., Contributing Writer 
Craig Freudenrich, Ph.D., is a freelance science writer and former senior editor at HowStuffWorks. He earned a B.A. in biology from West Virginia University and a Ph.D. in physiology from the University of Pittsburgh School of Medicine before completing eight years of postdoctoral research at Duke University Medical Center.

https://science.howstuffworks.com/transport/flight/modern/air-traffic-control.htm

 

ELECTROMAGNETS - An electromagnet is created when electrical currents flow around some ferromagnetic core. The Earth’s core is iron, and we know it has a North Pole and a South Pole. A compass always points north because the metal needle is attracted to the pull of the North Pole. There's a wide range of electromagnet applications between small, homemade science experiments and the Earth itself. Many electromagnets have an advantage over permanent magnets because they can be easily turned on and off, and increasing or decreasing the amount of electricity flowing around the core can control their strength.

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Electromagnets

How Electromagnets Work

BY MARSHALL BRAIN & LANCE LOOPER

What do a wrecking yard, a rock concert and your front door have in common? They each use electromagnets, devices that create a magnetic field through the application of electricity.

Wrecking yards employ extremely powerful electromagnets to move heavy pieces of scrap metal or even entire cars from one place to another.

Your favorite band uses electromagnets to amplify the sound coming out of its speakers.

And when someone rings your doorbell, a tiny electromagnet pulls a metal clapper against a bell.

Mechanically, an electromagnet is pretty simple.

It consists of a length of conductive wire, usually copper, wrapped around a piece of metal.

Like Frankenstein’s monster, this seems like little more than a loose collection of parts until electricity comes into the picture.

But you don’t have to wait for a storm to bring an electromagnet to life. A current is introduced, either from a battery or another source of electricity, and flows through the wire.

This creates a magnetic field around the coiled wire, magnetizing the metal as if it were a permanent magnet.

Electromagnets are useful because you can turn the magnet on and off by completing or interrupting the circuit, respectively.

Before we go too much farther, we should discuss how electromagnets differ from your run-of-the-mill "permanent" magnets, like the ones holding your Popsicle art to the fridge.

As you know, magnets have two poles, "north" and "south," and attract things made of steel, iron or some combination thereof.

Like poles repel and opposites attract (ah, the intersection of romance and physics).

For example, if you have two bar magnets with their ends marked "north" and "south," the north end of one magnet will attract the south end of the other.

On the other hand, the north end of one magnet will repel the north end of the other (and similarly, south will repel south).

An electromagnet is the same way, except it is "temporary" -- the magnetic field only exists when electric current is flowing.

The doorbell is a good example of how electromagnets can be used in applications where permanent magnets just wouldn’t make any sense.

When a guest pushes the button on your front door, the electronic circuitry inside the door bell closes an electrical loop, meaning the circuit is completed and “turned on.”

The closed circuit allows electricity to flow, creating a magnetic field and causing the clapper to become magnetized.

The hardware of most doorbells consist of a metal bell and metal clapper that, when the magnetic charges causes them to clang together, you hear the chime inside and you can answer the door.

The bell rings, the guest releases the button, the circuit opens and the doorbell stops its infernal ringing. This on-demand magnetism is what makes the electromagnet so useful.

In this article, we’ll take a closer look at electromagnets and discover how these devices take some pretty cool science and apply it to gizmos all around us that make our lives easier.

The History of Electromagnets

The relationship between electricity and magnetism wasn’t thoroughly studied until 1873 when physicist James Maxwell observed the interaction between positive and negative electrical charges [source: Mahon].

Through continued experimentation, Maxwell determined that these charges can attract or repel each other based on their orientation.

He was also the first to discover that magnets have poles, or individual points where the charge is focused.

And, important for electromagnetism, Maxwell observed that when a current passes through a wire, it generates a magnetic field around the wire.

Maxwell’s work was responsible for many of the scientific principles at work, but he wasn't the first scientist to experiment with electricity and magnetism. Nearly 50 years earlier Hans Christian Oersted found that a compass he was using reacted when a battery in his lab was switched on and off [source: Gregory].

This would only happen if there were a magnetic field present to interfere with the needle of the compass, so he deduced that a magnetic field was generated from the electricity flowing from the battery.

But Oersted gravitated toward the field of chemistry and left the research of electricity and magnetism to others [source: Mahon].

The granddaddy of electromagnetism is Michael Faraday, a chemist and physicist who architected many of the theories later built upon by Maxwell.

One reason Faraday is so much more prominent in history than Maxwell or Oersted is probably due to his being such a prolific researcher and inventor.

He is widely heralded as a pioneer in the area of electromagnetism, but he is also credited with discovering electromagnetic induction, which we will discuss later when we explore some real-world applications.

Faraday also invented the electric motor, and besides his influential work in physics he was also the very first person to be appointed the prestigious position of Fullerian Professor of Chemistry at the Royal Institution of Great Britain. Not too shabby.

So what did the work of these men uncover? In the next section, we’ll look at how electromagnets work.

Putting the “Electro” in “Electromagnet”

Since an electrical current is required to operate an electromagnet, where does it come from?

The quick answer is that anything that produces a current can power an electromagnet.

From the small AA batteries used in your TV remote to large, industrial power stations that pull electricity directly from a grid, if it stores and transfers electrons, then it can power an electromagnet.

Let’s start with a look at how household batteries function.

Most batteries have two easily identifiable poles, a positive and a negative. When the battery isn't in use, electrons collect at the negative pole.

When the batteries are inserted into a device, the two poles come into contact with the sensors in the device, closing the circuit and allowing electrons to flow freely between the poles.

In the case of your remote, the device is designed with a load, or exit point, for the energy stored in the battery [source: Grossman].

The load puts the energy to use operating the remote control. If you were to simply connect a wire directly to each end of a battery with no load, the energy would quickly drain from the battery.

While this is happening, the moving electrons also create a magnetic field. If you take the batteries out of your remote, it will likely retain a small magnetic charge.

You couldn’t pick up a car with your remote, but maybe some small iron filings or even a paper clip.

On the other end of the spectrum is the Earth itself.

By the definition we discussed earlier, an electromagnet is created when electrical currents flow around some ferromagnetic core.

The Earth’s core is iron, and we know it has a North Pole and a South Pole. These aren't just geographical designations but actual opposing magnetic poles. 

The dynamo effect, a phenomenon that creates massive electrical currents in the iron thanks to the movement of liquid iron across the outer core, creates an electrical current.

This current generates a magnetic charge, and this natural magnetism of the Earth is what makes a compass work.

A compass always points north because the metal needle is attracted to the pull of the North Pole.

Clearly, there's a wide range of electromagnet applications between small, homemade science experiments and the Earth itself.

So, where do these devices pop up in the real world? In the next section, we’ll take a look at how our everyday lives are affected by electromagnetism.

Electromagnets All Around Us

Many electromagnets have an advantage over permanent magnets because they can be easily turned on and off, and increasing or decreasing the amount of electricity flowing around the core can control their strength.

Modern technology relies heavily on electromagnets to store information using magnetic recording devices.

When you save data to the hard drive in your computer, for example, tiny, magnetized pieces of metal are embedded onto a disk in a pattern specific to the saved information.

This data started life as binary digital computer language (0s and 1s). When you retrieve this information, the pattern is converted into the original binary pattern and translated into a usable form.

So what makes this an electromagnet? The current running through the computer’s circuitry magnetizes those tiny bits of metal.

This is the same principal used in tape recorders, VCR’s and other tape-based media (and yes, some of you still own tape decks and VCRs). This is why magnets can sometimes wreak havoc on the memories of these devices.

Electromagnets also paved the way for really harnessing the potential of electricity in the first place.

In electrical appliances, the motor moves because the current flowing from your wall socket produces a magnetic field. It’s not the electricity itself powering the motor, but the charge created by the magnet.

The force of the magnet creates rotational movement, which means they rotate around a fixed point, similar to the way a tire rotates around an axle.

So, why not skip this process and just use the outlet to power the motor in the first place? Because the current required to power an appliance is quite large.

Have you ever noticed how turning on a large appliance such as a television or a washing machine can sometimes cause the lights in your home to flicker?

This is because the appliance is drawing a lot of energy initially, but that large amount is only needed to get the motor started.

Once that happens, this cycle of electromagnetic induction takes over.

From household appliances, we're moving up to some of the most complex machinery ever built to see how electromagnets are being used to unlock the origins of the universe.

Particle accelerators are machines that propel charged particles toward one another at incredibly high speeds in order to observe what happens when they collide.

These beams of subatomic particles are very precise and controlling their trajectory is critical so they don’t go off course and damage the machinery. This is where electromagnets come in.

The magnets are positioned along the path of the colliding beams, and their magnetism is actually used to control their speed and trajectory [source: NOVA Teachers].

Not a bad resume for our friend the electromagnet, huh? From something you can create in your garage to operating the tools that scientists and engineers are using to decipher the origins of the universe, electromagnets have a pretty important role in the world around us.

https://science.howstuffworks.com/electromagnet.htm

 

ARCHIMEDES SCREW - A circular pipe enclosing a helix and inclined at an angle of about 45 degrees to the horizontal with its lower end dipped in the water; rotation of the device causes the water to rise in the pipe. Modern screw pumps, consisting of helices rotating in open inclined troughs, are effective for pumping sewage in wastewater treatment plants. The open troughs and the design of the screws permit the passage of debris without clogging.

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Archimedes Screw

WRITTEN BY: The Editors of Encyclopaedia Britannica 

Archimedes screw, machine for raising water, allegedly invented by the ancient Greek scientist Archimedes for removing water from the hold of a large ship.

One form consists of a circular pipe enclosing a helix and inclined at an angle of about 45 degrees to the horizontal with its lower end dipped in the water; rotation of the device causes the water to rise in the pipe.

Other forms consist of a helix revolving in a fixed cylinder or a helical tube wound around a shaft.

Modern screw pumps, consisting of helices rotating in open inclined troughs, are effective for pumping sewage in wastewater treatment plants.

The open troughs and the design of the screws permit the passage of debris without clogging.

https://www.britannica.com/technology/Archimedes-screw