September 3rd, 2010 | 
Author: Equipment lease takes many forms. Equipment finance lease is one of these forms, which differ from the ordinary lease in that, the equipment is bought specifically for the company intending to lease it.
Sometimes you find companies requiring certain equipment. However, due to different factors the company might not be able or willing to raise the capital amount required to cover the cost. Normally a business will not function properly without the necessary capital equipment, which can range from simple office furniture to heavy plant machinery. The company might also need the equipment only for a limited period and therefore purchasing them would be a waste of resources. Finally, there might be some benefits associated with leasing the equipment rather than purchasing them leading the company to opt for the lease. Some of the common benefits that would lead to such a decision include tax benefits and elimination of unexpected repair costs that keep on coming up.
In ordinary equipment lease arrangements, the company hires the equipment for a given period only. There is also the option to upgrade to new or more advanced equipment if you can afford the new rates charged. This arrangement favors the company because the equipment will not appear in the balance sheet and it will enjoy the benefit of no depreciation. This makes it quite different from the equipment finance lease, which allows one to claim depreciation, running costs and interest payments from the running costs of the business.
Implications of Equipment Finance Lease
An equipment finance lease is the arrangement, which helps the company to acquire the required equipment easily on lease. With this arrangement, the company will be required to identify the equipment that is required. The company will also need to choose a finance firm, which will purchase the asset. The company will then be able to use the equipment during the lease period paying installments or rentals for the use of the equipment. Both parties benefit from this arrangement, as the finance company is able to recover the amount or a large part of the cost and also earn interest from the rental. The company will have benefited from the use of the equipment without necessitating purchase. At the end the company has the option of gaining ownership for the equipment either through payment of the last installment or through negotiation for a given purchase price.
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People are a notoriously self-interested lot. They avoid activities that don’t benefit them, skip events that bore them and reject content that doesn’t interest them in some way. They aren’t going to go out of their way to read up on an article simply because it has all the information the author thinks is vital and important if they personally feel that article is a waste of their time. Indeed, nothing is a surer waste of someone’s time than a crappy, poorly assembled article. A piece of copy could have the very recipe for successful nuclear fusion buried on page 14, but if it bored readers away on page 9, no one will ever dig deep enough to find it and society will continue to churn out dirty coal and uranium waste.
This raises the natural question: What exactly is “crappy” content? The short and almost tautological answer is “content that people don’t like,” but simply saying that doesn’t get a writer anywhere. There are many kinds of crappy content, each with its own unique reasons for being a dull and uninteresting lump rather than a well-polished gem of online commentary.
Type 1 – SEO Smash
First, let it be said that there are few techniques as important to online brand marketing at this time than Search Engine Optimization. Google rightly can claim to rule the web by means of its indexing power. A recent merger between Microsoft’s software and the Yahoo! search engine was described in terms of its ability to challenge the reigning king, Google, not on its own merits. So, the ability to get content noticed by search engines through the use of keywords, meta tags and proper formatting is all a vital portion of the content process.
However, any article first approached from the angle of creating an SEO-perfect piece, rather than with a focus on presenting an existing idea through the lens of an SEO effort, is going to get called out as crap. SEO-centric writing leads to articles that are little more than keyword phrases badly hashed together with poor grammar and unusual contortions of the English language, and people notice this kind of writing. They might pop by for a look, but they won’t stick around. First have something to say, then learn the best way to say it.
Type 2 – Humor Bludgeon
There’s a trend on the web for articles to be entertaining, funny and even to an extent snarky or sarcastic. This trend can be seen in the success of biting commentary sites such as Something Awful or the new Rifftrax DVDs (a series dedicated entirely to making fun of poorly-made movies).
Everyone wants to imagine they’re a clever, witty genius who can turn a fairly dull piece of writing into biting social commentary and satire. Most of these people are not such paragons of humor, however. Instead, their writing comes across as forced and scraping for obvious jokes that seem tired and strained. As a rule of thumb, if a funny turn of phrase comes to mind on its own, a writer should feel free to give it a try. If the writer has to consciously think about how to make something sound funny, it probably doesn’t need to sound funny – and doesn’t belong in the article.
Type 3 – the Meme Beam
A variation on the topic of humor and witty banter above, memetics is a theory of social information transmission. Memes are ideas that are passed and replicated between people, and on the web they tend to take the form of popular sayings or pictures that catch on and go viral. Caturday is a meme, being the tendency of people to post funny pictures about cats on Saturdays. Other memes reference an imagined rivalry between pirates and ninjas, zombie apocalypses and other esoteric topics of web discussion.
A well-referenced meme can make an article more entertaining. A forced meme gets nothing more than rolled eyes and a disparaging snort in most cases, and quickly-spread criticism in the worst instances. Unless there’s a compelling reason to include a meme – such as a particular target audience, or the fact that your brand focuses on a specific meme – don’t try.
Type 4 – Sound and Fury, Signifying Nothing
Few things are more irritating than wasting someone’s time. The above examples are bad, and each one can lead to an article being dismissed, but they are also forgivable and won’t produce as virulent a reaction as presenting someone a piece of content that does them no good at all. Avoid this trap with all possible effort and ingenuity, because the moment it gets out that a brand has nothing to contribute, that brand is finished.
Instead, make sure every piece of content put up as part of a brand contributes something to the lives of the readers or viewers absorbing the content in question. Provide a tip about acquiring the product, a handy maintenance routine for keeping it running or even a story explaining how the brand has learned from its mistakes in its latest ad campaign and that it’s listening to the audience. Do something to contribute to the conversation. If the brainstorming meeting can’t say in less than 2 minutes why a particular piece of content is going up, don’t put it up.
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About the Author:
Enzo F. Cesario is an online branding specialist and co-founder of Brandsplat, a digital content agency. Brandsplat creates blogs, articles, videos and social media in the “voice” of our client’s brand. It makes sites more findable and brands more recognizable. For the free Brandcasting Report go to http://www.Brandsplat.com or visit our blog at http://www.ibrandcasting.com
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If you own and operate a small business, then the tools that allow you to conduct that business are your lifeline. Whether that equipment is a brush hog, combine harvester or state-of-the-art printing machine, the performance of that machine directly impacts your bottom line. While each piece of machinery is vital to your bottom line, that does not always mean you have the funds to buy a new piece of equipment as needs arise or old equipment breaks.
What can you do when you find yourself in need of a multi-thousand dollar piece of machinery? Or even equipment in excess of hundreds of thousands of dollars? There are options for business owners who have extended all their capital. If your business has a limited amount of capital to draw from, then choosing which equipment to buy and which to lease is a calculated choice; both sides have pros and cons. Here are a few of the advantages of leasing equipment rather than financing equipment or buying it.
First of all, the lifespan of the machine or equipment should be a major factor into when you take out equipment loans and when you lease. If you are looking at a machine with a lifespan of 10 or 20 years, then it may be in your best interest to use your capital or seek equipment financing to go ahead with an outright purchase of such an item. But let’s face it, there are very few machines that last that long or stay relevant for that long. If your business is such that it must stay current with developing technologies, then leasing is the perfect way to keep up with the latest tools.
Leasing does come with less initial cost, which means you will be able to save that capital for other expenses, upgrades or investments that come along. Most lease terms do not require a down payment or collateral, so you can keep all your liquidity and not affect your cash flow.
While you may have some savings up front, the long term cost is usually guaranteed to be more than it would have been if you purchased it. Even taking out business equipment loans can be a cheaper option than leasing. Although equipment leasing options typically have flexible terms, the financing is not usually as favorable as the loans you may be able to secure through your business. However, if you are a new business or have exhausted your lending options, then leasing is a viable choice for you. You can assess your financing options on a case by case basis, as each business and purchase will vary.
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If you love to make vintage crochet designs, but find that good patterns are difficult to find, then this could be the best website you’ve ever surfed into!Grab A Copy Click here
I’ll be honest, I love crocheting and knitting…unfortunately I’m not very good. I’m definitely still a beginner, but what I’ve found frustrating is the patterns I find are all the same, boring stuff, over and over. Have you noticed the same thing? Once in a blue moon you might find a great vintage pattern that actually has some bit of personality, but it ain’t easy.
So, I took it upon myself to find some awesome vintage crochet designs. It wasn’t easy, it took several months to compile the collection that is here…but I succeeded! And I’m offering this package to you, so you can spend your time crocheting, not looking for patterns!
How do I know? Because I looked (and looked and looked). Don’t get me wrong, I’m definitely not a crochet expert. In fact, like I said, I have more enthusiasm than actual talent. But what I am good at is finding amazing resources…like the antique books that contributed to this collection of crochet patterns.
All of the fantastic patterns in this collection are over 100 years old! That’s why I call them *true* vintage crochet patterns.
Here are just a few of the possibilities you’ll discover with this collection…
Create a one-of-a-kind Bridal Purse, for yourself, or for a gift…
Pamper that New Baby with a Beautiful Bassinet Counterpane!
Crochet Unique Anti-macassars to Complement Your Antiques…
Make Fantastic Netted Purses, to keep or to sell!
Craft Point Collars, to Personalize Your Blouses and Jackets…
Make Beautiful Crochet Insertions for Your Patterns!
Crochet Elegant Pincushions…
Make Stunning Window Curtains!
Create Treasured Afghans for Family Members!
Make Stunning Sofa Pillows…
Crochet one-of-a-kind Smoking Cap to match your Tobacco Bags! (ok, still couldn’t resist)
Make the Bride-to-be that you know a Pair of Lady’s Half-Hand Mitts…
Hand-Crocheted Garters? Can’t Find Those in Victoria’s Secret!
Grab A Copy Click here
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About the Author:
There’s a hidden cause of back pain… it’s something very few medical or healthcare professionals are even aware of… If they were, they wouldn’t be treating conditions.
Instead, they’d be identifying and addressing what brought about the condition in the first place.
For example, if you were diagnosed with a herniated disc, instead of just treating the symptoms, they should be finding out what caused the disc to herniate to begin with.
If you are like most people, you move around and live your life without ever being aware that you are forcing your body to work with these dysfunctions, and sooner or later your body breaks down.
An example of a dysfunction can be seen in the illustration below and as you can see, there is an excessive curve in the lower spine.
As you can imagine, it doesn’t take long before this results in pain. It’s very important to understand though, that these dysfunctions don’t just appear out of nowhere – we create them!
What the heck is a muscle imbalance you ask? When a muscle or group of muscles overpowers the opposing muscle(s), you have a muscle imbalance. Think of it as a Tug-of-War.
When your muscles are out of balance they pull your bones and joints out of their normal position and this places them under constant and uneven stress.
There are several things that contribute to and create muscle imbalances such as how active you are, what activities you do frequently, if you exercise, the exercises you perform, how you sit, stand and walk, if you work, what you do for work, etc.
Also, it’s very important to note that everyone has muscle imbalances and as you may have already realized, muscle imbalances are responsible for more than just back pain and sciatica. But just to make sure you understand and grasp this concept, here’s a quick analogy to help drive home the point.
What happens when you drive your car with unbalanced tires or your steering out of alignment? Your tires will wear down unevenly and quicker than normal and eventually you’ll have a blowout… the same is true for your body!
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YOU can join Instrumentmaster for both Violin and Piano for a small, ONE-TIME payment. You will then get INSTANT ACCESS to the program, and our members section which is here THOUSANDS of lessons in all styles are in our database, with pieces of music and other valueable resources. No catch, no recurring fees and NO LIMITS!!! Members of our site can also reach us 24-7 on my phone with AIM. We upload new lessons and techniques every week and add new resources every month. I’ll say it again! -IT IS JUST A COUPLE BUCKS FOR THE WHOLE THING! -You dont have to pay for each lesson. -You get all of them. I’ll see you in the members section.
Our navigation system is extremely simple: You simply register, then you will be automatically granted access to the members section. The members section consists of the main instrument schools, Resource banks and daily updates. Once you access which instrument you would like to study, you will be given a choice of which level and style.
Jay Dynasty and Greg Evans have both been teaching music for 15 years.NO HIDDEN FEES! -Sign up for a membership and study with us forever. with absolutely no re-occurring charges!
Can I pick one style or instrument and then drop it and pick up another one?Yes you can pick and choose as you like and we have over 10 styles and genres of instruction for each instrument.
A great place to start you advertising campaign is Google Adwords and other pay-per-click search engines. If you are new to PPC search engines or would just like a great lesson in making google ads that sell like Crazy, try reading this fabulous E-Book: GOOGLE ADWORDS 123 . If you want to make a real living doing this get ADWORD EQUALIZER.
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LET THERE BE A RIGHT TO EARN A LIVING
Let there be a right to earn a living!
All who wish to work should have the chance.
Bad times come and go with circumstance:
Ought we then be hiring or just giving?
Rest assured, there’s always much to do:
Demand’s determined more by funds than need.
All we give away is wealth we bleed,
Yet work for wages would that wealth renew.
LIFE IS BEAUTIFUL, MY CHILD
Life is beautiful, my child,
Though many things go wrong,
And you may hear much sadness in
Its strange and lovely song.
Though friends and loved ones die, my child,
They’re never really gone.
Nor more nor less than yesterday,
In you they will live on.
They will live on in you, my child,
As everything you see,
Though it must vanish, will remain
Alive in memory.
Alive in what you think and feel
And dream and say and do,
For all who ever were still are
Upon this earth in you.
MARRIAGE, AS A CHOICE, REQUIRES CHOICES
Marriage, as a choice, requires choices.
One must choose not once, but every day.
Life offers us a hundred thousand voices,
Yet those we fail to hear fast fade away.
I choose you with all my wounded heart:
You and our two children. All the rest
Lies in the distance, charming, but apart
From the circle of the ones with whom I’m blessed.
Our marriage isn’t easy, but our love
Is still the force that shapes my daily life.
I want us to be happy, and will move
Wherever I must be to be your wife.
I’m yours, and I want you to be mine.
We’ll find a way our wishes to combine.
LET’S NOT MINIMIZE THE ROLE OF THUGS
Let’s not minimize the role of thugs
And gangsters in the history of labor.
Beasts and saints together weave the rugs
On which we walk, and ordinary folk
Rendering allegiance to whomever.
Desperate now, the unions bear the yoke
Abjectly of their presidents-for-life.
Yet workers still must organize and strike.
ROSH HASHANA OPENS UP THE BOOK
Rosh Hashana opens up the book
Of life, that we might be inscribed therein.
So does the will work wonders with the wind,
Hallowing the leaves that tempests shook.
How might we make our peace with death and pain?
As terror stalks our steps, how might we dance,
Singing through the vales of circumstance,
However dark or haunted by the slain?
All we have are justice, hope, and love,
Nor will these weak or insufficient prove
As we repent our anger once again.
TWENTY-FIVE YEARS, AND STILL YOU ARE IN LOVE
Twenty-five years, and still you are in love!
What river does not deepen as it flows?
Each day your love increases as it goes,
Nourishing the lands through which it moves.
The love that lasts is deeper far than passion.
Years pass and it abides beneath the light.
Few know the secrets of its dark delight,
Intent on all the toys that are in fashion.
Vivid lusts yield pleasures that soon cease.
Each year of love yields happiness and peace.
THERE IS NO GIFT MORE PRECIOUS THAN ONE’S HEALTH
There is no gift more precious than one’s health.
Happiness must rest upon that ground.
Alight with pain, no pleasure can be found,
Nor joy in love or beauty, words or wealth.
Know that I am grateful for your skill,
Your sensitivity and dedication.
Out of strength, I dreaded all sensation
Until your healing touch restored my will.
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About the Author:
Nicholas Gordon is a poet and the webmaster of the popular poetry site, Poems for Free at http://www.poemsforfree.com. He holds a Ph.D. in English and American Literature from Stanford University. For most of his working life, he taught English at New Jersey City University, in Jersey City, NJ.
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To make a living as a freelance writer, you must learn to think profit. Freelance writing is a job. It requires self-control, dedication, a business plan, and personal goals. If you are not willing to labor long hours for little pay, you are not likely to succeed as a freelance writer. If you are not willing to study, learn, and apply the rules of grammar, you are not likely to succeed as a freelance writer. If you do not practice self-editing, you are not likely to succeed as a freelance writer. If you are only willing to write what pleases your inner muse, you are not likely to succeed as a freelance writer.
Two Types of Free Articles
Setting aside the special conditions that pertain to novels and short stories, this article focuses on Internet related content writing. Furthermore, we will temporarily ignore the interests of Search Engine Optimized (“SEO”) writing goals. Thus we are left with only two types of free Internet article materials:
1. Self-promoting. An author sometimes writes to enhance his personal and professional reputation. The speed of article output is directly proportional to a writer’s knowledge in the given subject area. Data research costs time and money. Yet a wise professional will post on a wide range of subject matter. This helps establish an expanded skill level. Self-promoting articles should display your adaptability as well as your authoring skills.
2. Passion writing. In heart, I am a Christian writer. I post Christian articles with the single goal of furthering the gospel of Jesus Christ. It has nothing to do with profit, status, or personal reputation. Passion writing promotes a subject that is dear to the heart of the writer. Although a passion article can provide income, the writer truly creates the material merely because it reflects who he is.
A note before moving on: I use the word “free” to describe any material that receives a pay rate that is less than one cent per word. Even at permitting “one cent” to be a mark of income, I am stretching the definition of paid writing.
Avoid The Scams
The freelance writing field is littered with scam artists. Unless you are deliberately publishing through an article submission site, and this only as a means of more quickly reaching your name recognition goals, avoid any site that ask that you pay for leads, pay to be published, or pay for promotional help.
Also look out for the Private Label Rights (“PLR”) group, especially those who claim they can teach you how to write four and five hundred word articles in five or six minutes. Run-of-the-mill materials will not establish a lasting reputation for quality. Rather than earning a living as a professional freelance writer, you will end up trying to manage a website that sells PLR overloads.
Finding The Income
Article marketing is a profitable business, but it has a huge downside: The Internet is bloated with writer job-boards that are patronized by a low-paying customer base. Many of the writers who seek work through a bid-based job site will end up working for less than free. Sample article requests are a standard job-board scam.
Several professional, writing service sites also populate the Internet. These are pay-per-article websites that do not include any form of bidding or guesswork. Customers place an order, and any freelancer that is linked-in to the writer service has an opportunity to select and write that job. Writer service websites normally offer a varying payment plan that is based upon the accepted professional quality-level of the author. The entry-level pay may be as low as ½ cent per word, but if a writer can produce consistent excellence in product, it is possible to make five to ten cents per word through an article service platform.
As a final method of finding writing income, consider establishing your own writing service website. This is a time consuming task, and it will require that you produce and publish many free articles for the non-paying and the low-paying author websites. However, if an author can establish a sufficient reputation for quality and service, the customers who respect successful work will seek you out, and they are willing to pay for quality.
Building A Reputation
The following tips are presented without explanatory side notes. If you do not understand these tips, use them as research pointers. Let the training begin. To produce a successful article you must:
Write useful information that answers relevant questions
Eliminate all fill material
Trim out any unnecessary words
Avoid a passive writing voice
Control the article length.
Use photos, illustrations, and web links only when and where they fit
Write effective and compelling SEO content
Identify, track, and write about popular topics
Setup a personal blog
Identify the article sites that match your focus, and then post often
Include a link to your blog, and your name, in every article resource box
Practice resource box switch-ups
Write fast, write often, but never sacrifice quality.
Remember: starting up a freelance writing business requires hard work and dedication. Freelance opportunities exist for web content writing, resume writing, copy writing, and more. Some fields, such as medical and legal, are more lucrative than other fields. They are also more difficult to learn and master.
Find your author’s niche, expand on it, and then start earning a living in the world of freelance writing.
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About the Author:
Hi, rmharrington here.
Thank you for reading my articles and stories. My goal is to glorify God, lift up the name of Jesus, and to provide quality-reading material.
Read about Website optimization here: http://www.associatedcontent.com/article/2721449/web_site_search_engine_optimization.html?cat=35.
Or
How to track the success of your labors here: http://www.associatedcontent.com/article/2757205/writing_how_to_track_your_writing_success.html?cat=35.
Thank you again.
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THE SCIENCE AND TECHNOLOGY OF AIR TRAFFIC CONTROL By Jamal Barki
Air Traffic Control
The typical image people have of air traffic control (ATC) is that of a group of people in an airport tower who coordinate aircraft activity by staring at radar screens that use points of light to represent aircraft. While not fundamentally incorrect, this isn’t a fair representation of the extent of ATC operations. This article will flesh out that simplistic image and introduce you to the equipment, technologies, and procedures that go into keeping aircraft and air travelers safe in the air and on the ground. We’ll look at the way air traffic control is organized, and explore the communication technologies that air traffic controllers use to keep in touch with air crew and ground personnel. We’ll also look at the radar technologies used to keep track of aircraft, and we’ll end with a brief look at some next-generation technologies.
Safety and wake turbulence
The primary mandate of air traffic control is to ensure the safe transport of people and cargo by keeping aircraft at a safe distance from each other and expediting the flow of traffic. Air traffic controllers have access to sophisticated radar systems that provide an overview of the airspace they control, and they have communication tools to coordinate flight paths with the air crew. Pilots lack the tools necessary to get an overview of the airspace, so they have to rely on air traffic controllers to guide the aircraft through congested airspace.
Since aircraft travel at significantly higher speeds compared to other common modes of transport, the time available for pilots to react to a dangerous situation can be quite short. Thus it’s essential that flight paths are carefully planned and managed to minimize the risk of a collision. This is especially true around major airports where the density of aircraft in a given volume of airspace is higher than average.
Turbulence created by wingtip vortices and exhaust gases from jet engines can be significant when aircraft are in close proximity. This phenomenon, called “wake turbulence,” can adversely affect trailing aircraft if the distance between them falls below a certain limit. This limit depends on the mass of the two aircraft. For instance, a light aircraft following a heavy aircraft is more susceptible to wake turbulence than a heavy aircraft in the same situation. Therefore, aircraft approaching an airfield have to be carefully sequenced in a manner that takes such factors into consideration. Additionally, weather conditions such as low cloud, heavy rain, or snow blizzards can mean that pilots can’t see other aircraft in the vicinity and have to use their instruments and instructions from air traffic control to navigate.
Types of ATC
Air traffic controllers are organized into various groups, each of which is in charge of handling a distinct portion of the aircraft’s flight. Each group has a designated airspace that it controls, and aircraft are handed off to the next group of controllers as it approaches the limits of the prior group’s airspace. The airspace controlled by each group is further divided into sectors that are themselves handled by individual controllers. The way these groups are organized varies from country to country and depends on the extent of controlled airspace and number of aircraft handled.
The Potomac TRACON facility controls approaches and departures in the airspace surrounding Baltimore Washington International, Washington Dulles, and Washington National airports.
The tower controllers are the most visible group. From their vantage point on the airport tower, they have a visual overview of all the important parts of the airport tarmac, such as runways and taxiways. Tower controllers monitor the airspace surrounding the airports and keep track of approaching and departing aircraft. At well-equipped airports, they may even have access to surface movement radar systems to monitor aircraft and support vehicles as they move on the ground.
Once the aircraft is in the air and clear of the airfield, tower control hands the aircraft off to a departure controller. These controllers are typically based at facilities a good distance from the airport. With the use of surveillance radars, they are able to monitor air traffic around the airport. These facilities are called Terminal Radar Approach Control (TRACON) facilities in the US. In an area like New York, where airports are close to one another, a TRACON facility can service multiple airports. The controllers here ensure that the planes approaching and departing the airspace they control are following designated flight paths and speeds. TRACON facilities also sequence the aircraft that are coming in to land, in order to ensure that they are adequately separated to minimize any wake turbulence effects. Departure controllers also need to take into account aircraft that may be flying through their airspace, and keep them separated from aircraft landing or taking-off.
As the aircraft exits the TRACON airspace, a facility known as an Area Control Center (ACC) takes over. These facilities monitor the aircraft’s flight while in controlled airspace through remote radar stations. Each ACC will have a designated airspace that it supervises. An aircraft may fly through multiple ACC sectors as it flies to its destination, with each ACC handing off control of the aircraft to the next ACC as it exits the former’s airspace. Once an aircraft gets closer to its destination airport, the ACC controllers hand off responsibility to the approach controllers at the local TRACON, who guide and sequence the aircraft to the active runway, and finally to the tower controllers.
ATC Radar Systems
Air traffic controllers use radar systems positioned at or near the ATC facility to get a real-time overview of the aircraft flying in the airspace they control. Radar technology for detecting aircraft first became popular during the wars in the first half of the last century and played a vital role in their outcome. First-generation radar systems served as early warning systems; these systems had relatively poor resolution, and their only purpose was to alert their operators to the presence of flying objects in the radar’s field of view. These early radars operated by emitting a continuous radio signal and listening for any echos, but they weren’t able to use these echos to gauge the size of the aircraft, calculate its ground speed or altitude, or determine if the aircraft belonged to an ally or the opposition.
After the war, radar technology was advanced with improved electronics and materials for antenna construction. This allowed for systems that were much more efficient and had higher resolution. The Air Traffic Controllers today are served by many types of radar equipment such as Primary Surveillance Radars (PSR), Secondary Surveillance Radars (SSR), and Mode S for monitoring traffic in the air, and Surface Movement Radars (SMR) for traffic on the ground.
Primary Surveillance Radar (PSR)
The Primary Surveillance Radar is the traditional form of radar that most people are familiar with. The radar sends a directed pulse into the atmosphere, and when that pulse encounters an object it gets reflected back to the radar station. By having precise knowledge of the orientation of the radar and the time between the sending and receiving of the radio pulse, the bearing of the object with respect to the radar station and its approximate distance can be calculated. The radar is typically enclosed in a dome to protect it from adverse weather. The PSR cannot determine the altitude or elevation of the aircraft relative to that of the radar station. For this to be possible, a second radar that sweeps the sky vertically would be required. However, such technology is typically only found in Precision Approach Radar installations at military facilities to assist pilots with landing aircraft.
The potential for an aircraft to be detectable by the PSR depends on its Radar Cross Section (RCS). The RCS depends on a number of factors, including the distance between the aircraft and the radar, and the size of the aircraft. A larger aircraft, for instance, would be visible at a greater distance than a smaller aircraft due to the larger surface area available for reflecting the radar waves. Other factors, such as reflectivity properties of the aircraft skin, the wavelength of the radar signal, and the angle at which the radar signal is incident on the aircraft (and thereby reflected), also play a part in how visible an aircraft is to the PSR.
Secondary Surveillance Radar (SSR)
The Secondary Surveillance Radar system—or Air Traffic Control Radar Beacon System (ATCRBS) as it is sometimes referred to—is comprised of the ATC radar installation and a transponder that rides onboard the aircraft being monitored. The origins of SSR lie in the “identify friend or foe” system used by the military to distinguish allied and enemy aircraft. While a Primary Surveillance Radar listens for reflected radio signals, the Secondary Surveillance Radar listens for messages from the aircraft’s transponder. The radar rotates about the vertical axis similar to a PSR, but transmits a specific signal on 1030 MHz. This signal is subsequently received by the aircraft’s onboard transponder, which responds with a reply on 1090 MHz. Much like the PSR, the bearing and distance of the aircraft with respect to the radar installation can be calculated with precise knowledge of the orientation of the radar when the signal was transmitted.
The SSR system has many advantages over PSR. Firstly, since it doesn’t rely on radio waves being reflected back by the aircraft, the radar cross section of the aircraft does not form a part of the equation. All aircraft in range of the radar, regardless of size, composition, or distance from the radar, can be “heard” equally well. Secondly, since the signal received by the radar originates on the aircraft, the signal is subject to less attenuation compared to a PSR signal. This is because the reflected PSR signal has to travel twice as much as the SSR signal. This also implies that the signal transmission power for an SSR can be much lower than that of a PSR.
While SSR has many advantages, the prime disadvantage is that the system needs a properly functioning transponder on the aircraft for it to work. An aircraft without a transponder would effectively be invisible to the SSR. For this reason, PSRs are still used as a backup mechanism in most parts of the world. The Federal Aviation Regulations (FAR) in the US (and similar regulations in most countries) require aircraft operating in air traffic controlled airspace to have an operational transponder.
SSR Modes
The signal transmitted by the SSR is termed the “interrogation signal.” There are different modes of interrogation that compliant transponders respond to. Civil aircraft typically respond to interrogation modes A and C.
In Mode A, the transponder responds with its squawk code, a unique identifier for the aircraft assigned by ATC comprising of four octal numbers. This code enables ATC to differentiate between the various aircraft being monitored, though it can also be used to discretely communicate the existence of an emergency situation onboard the aircraft. For instance, a squawk code of 7500 indicates that the aircraft has been hijacked, and a squawk code of 7600 indicates that the pilots are unable to communicate with ATC.
In Mode C, the transponder responds with the aircraft’s pressure altitude, which is the altitude above sea level as calculated using the barometric reading at the aircraft’s altitude. The altitudes reported are in 100-feet increments. This information is vital for ATC to ensure that aircraft flying in close proximity have adequate vertical separation.
Mode S is an improved secondary surveillance mode, and it operates over the same radio frequencies as SSR, making it backwards compatible. While Modes A and C in the legacy SSR system “broadcast” an interrogation message to all aircraft in the path of the radar beam, Mode S selectively interrogates individual aircraft using a 24 bit identifier that is assigned to the aircraft upon registration.
Mode S has a number of advantages over Modes A and C, the first of which is that its selective interrogation approach reduces the workload on the system, as it might be inundated with SSR replies in heavily congested airspace. Secondly, the legacy SSR system allowed for a transponder identification code of only four octal digits (12 bits) that yielded just 4096 codes (not including reserved codes) which were assigned by ATC. To complicate matters, this could be different for the same aircraft in different ATC sectors. As the number of aircraft increased over the past few decades, there was a scarcity in the number of available transponder codes, but move to a 24 bit addressing system alleviated the problem. Finally, the altitude reporting in Mode C was in increments of 100 feet, but this was improved to increments of 25 feet, allowing controllers to have a more accurate picture of aircraft positions.
Surface Movement Radar (SMR)
The airfield can be a busy place, with pushback tugs, tractors with baggage containers in tow, refuelling trucks, catering trucks, airport security vehicles, and (of course) aircraft. While the PSR and SSR provide controllers with an overview of aircraft in the air, the surface movement radar provides a real-time view of aircraft and support vehicles on the ground at airports. Most modern airports have Ground Control in charge of ensuring that critical patches of the airport tarmac such as active runways and taxiways are safe for moving aircraft.
Ground Control can observe all moving vehicles and aircraft on a radar screen overlaid on a map of the airport. As the objects being tracked by an SMR are relatively smaller than those tracked by a PSR or SSR, the radar uses a much shorter wavelength (and correspondingly higher frequency) with a narrow beam for a higher resolution result. Depending on the size of the airport, multiple installations of this sort may be required to cover all the critical parts of the airport. Enhancements to this basic system include having airport support vehicles installed with transponders that can be queried to ascertain location. Similarly, aircraft transponders can be queried to augment the radar display with call signs. Information from the tower radar can also be incorporated to display approaching aircraft. Newer systems can even aurally warn controllers of potential runway incursions and conflicts, so that action can be taken in time to avoid disaster. Such a system is generally called an Airport Movement Area Safety System.
Unfavorable weather conditions such as heavy rain and fog can lead to a reduction in visibility, making it difficult to monitor the tarmac. Runway incursions are a constant danger in such challenging conditions. A runway incursion is described by ICAO (International Civil Aviation Authority) as the incorrect presence of an aircraft, vehicle, or person on the protected area of a surface designated for the landing and take-off of aircraft. The Tenerife Airport Disaster, the deadliest accident in aviation history, was as a result of two aircraft colliding with each other on the runway. The incident occurred in heavy fog and at a time when the air traffic controller on duty could not see the two aircraft, nor could the two pilots see each other. A more recent incident that highlights the importance of the surface movement radar in emergency situations is the crash of british airways flight 038 on the threshold of runway 27L at London Heathrow Airport.
Air-Ground Voice Communication
In the early years of aviation, when there were fewer planes in the sky than we have today and there was not much need for pilots to communicate with ground personnel, signalling was often done using lights and flags. But with an increase in aircraft, a more efficient and unambiguous two-way communication system became necessary. At the same time, radio technology was progressing, and it became feasible for aircraft to have radio transceivers on board.
Aircraft communication in the early years was over the HF (High Frequency) range of the radio spectrum. In the US, each airline company had its own dedicated radio frequency over which company pilots communicated with their operators on the ground. But over time, with an increase in airliner companies and air traffic, this system soon led to a depletion in the available frequencies on the spectrum. The problem was resolved by setting up a common entity that provided air traffic coordination services. This allowed for a better use of the available radio spectrum, as pilots communicated with air traffic personnel over common frequencies. Over time, this system evolved to the air traffic control system we have today.
Modern civil aviation uses the HF (High Frequency) and VHF (Very High Frequency) parts of the spectrum for communication between aircraft and ATC. Military aviation in various countries are also known to operate in UHF (Ultra High Frequency). Early air to ground voice communication was over HF, but VHF started to get adopted in the 1930s and 1940s.
VHF communication
VHF is the predominant frequency range used by civil aviation in most parts of the world, and communication usually happens over the 118 MHz to 138 MHz frequency range via an amplitude modulated (AM) signal. (FM radio, in comparison, is over frequencies from 87 MHz to 108 MHz in most countries, and is of course, frequency modulated.) The frequency 121.5 MHz is reserved for emergencies in the VHF frequency range.
VHF transmissions rely heavily on a line-of-sight between the transmitter and receiver. This doesn’t necessarily mean a visual line-of-sight, however, but a “radio line-of-sight” in the VHF part of the spectrum. Solid structures, such as buildings or the earth’s surface, tend to attenuate the signal (or reduce its strength). Additionally, atmospheric layers do not refract or reflect VHF waves well. Due to these characteristics of VHF propagation, and due to the curvature of the earth, an aircraft below a VHF transmitter’s radio horizon would typically fall outside its range. Thus the nature of the terrain and the height of the aircraft above the ground plays a part in determining whether it is in range of a given ground station operating over VHF frequencies.
For instance, the range would be severely curtailed for low-flying aircraft in hilly areas or urban areas with tall skyscrapers. In such cases, signal repeaters can be used to increase coverage. Theoretically, an aircraft at cruise altitude, flying in ideal weather conditions with a good quality transceiver can expect to communicate with a station unobstructed by hilly terrain about 200 nautical miles away (370 kilometers or 230 miles). In less than ideal real-world conditions however, this range can be significantly lower.
VHF operating frequencies are allocated to ATC stations in such a way that they do not interfere with each other, and since VHF relies on line-of-sight, frequencies can be reused by other distant stations. A typical activity for controllers is to pass on the frequency used by the next ATC sector to the pilot as the aircraft exits the ATC’s airspace.
HF communication
When flying over large expanses of water, VHF communication, due to its line-of-sight nature becomes unusable. Additionally it would be impractical to construct, operate and maintain VHF relay stations in the middle of the ocean. So in these situations, HF can be used to communicate with an aircraft below the station’s horizon and often many thousands of nautical miles away. In some cases, HF transmissions are known to have been successfully received on the other side of the planet. Thus pilots flying certain oceanic routes that are outside radar coverage use HF to periodically report their position to the oceanic control station for the sector they are flying in.
HF has some major drawbacks that make it impractical for more widespread applications. First, HF signal propagation is highly dependent on atmospheric conditions and solar activity, making HF communication comparatively noisy and unreliable. Due to this variability, ATC stations operating over HF have a number of alternative frequencies that they can operate over, and they switch to the frequency with the best signal propagation characteristics at the time.
It’s also the case that HF signals have a longer wavelength than VHF signals, so the antennas used for transmitting and receiving are much larger, as well. And HF transmitters also operate at a higher power, since the receivers may potentially be hundreds of nautical miles away.
Next-generation Technologies
The aviation industry has been relatively conservative in its approach to adopting new technologies, so a number of the systems described so far are based on technology that has been around for at least a few decades. This conservatism is primarily attributable to the safety and reliability considerations that must be taken into account when making changes to existing equipment and procedures.
While tried-and-true systems do provide the required safety, this safety may at times come at the cost of efficiency. Critics of the current air traffic control systems claim that efficiency gains of many percentage points remain to be realized by more intelligent routing in controlled airspace that allows for lower separation distances between aircraft.
Currently, the Federal Aviation Administration (FAA) in the US is studying the implementation of various next-generation technologies to improve the efficiency of the ATC system while retaining or improving the level of safety. Next generation will incorporate global positioning satellites, digital communication networks, data networking, and improved weather forecasting to improve efficiency. Of all the technologies being considered, Automatic Dependant Surveillance (ADS-B) is being billed as the the future of air traffic control and as the backbone of the NextGen system.
Automatic Dependant Surveillance—Broadcast (ADS-B)
ADS-B is a relatively new technique (compared to use of primary and secondary surveillance radar) to monitor aircraft. The technique uses the global positioning system (GPS) to provide an accurate report of an aircraft’s position. As the name suggests, this is a broadcast technique where an aircraft equipped with an ADS-B transponder routinely broadcasts data. Using similar information from all aircraft, the air traffic controllers can build an accurate picture of aircraft positions. ADS-B is able to provide information not unlike an SSR, but without the requirement for a radar installation or transmissions from a ground station.
The aircraft typically transmits its identity, current position, speed, and direction of travel (among other parameters) over a digital link, twice every second. Due to the broadcast nature of the data, other aircraft in the region can also receive this information and provide their pilots with an overview of the traffic in the neighborhood as well. One of the advantages of the ADS-B system is that the receiver can be relatively simple and inexpensive. Another advantage is that ground vehicles at the airport can use the same system to report their location on the airport tarmac which can be incorporated into the Airport Movement Area Safety System described earlier.
One of the disadvantages of ADS-B is that the system relies on the GPS system for accurate reporting of position information. Loss or degradation of the GPS signal could potentially put lives in danger. This can be mitigated to an extent by alternative sources of positioning information such as the European Galileo project, the Russian GLONASS project or the Chinese Beidou project, when they become fully operational. The other disadvantage is that a malfunctioning or inoperative transponder could render the aircraft invisible, or worse, broadcast false information. This is one reason for the continued use of surveillance radars as backup. Given the relative simplicity and cost-effectiveness of building an ADS-B transponder (compared to surveillance radars) and the open nature of the system, critics fear it is also a security hazard as it would in theory be possible to spoof data to represent aircraft that don’t actually exist.
Listening to ATC and Tracking Aircraft
ATC and pilots communicate over open, well-advertised frequencies. Since VHF communication takes place using frequencies between 118 MHz to 138 MHz, a frequency range not commonly available on general purpose radio receivers, a scanner that can tune into these frequencies is required. It isn’t unusual for serious aviation enthusiasts to invest in a good quality scanner to listen to their local air traffic controllers and pilots. Sites such as live ATC stream ATC broadcasts from various ATC facilities in the world. One must, however, exercise caution and check local laws first, as listening to ATC is illegal in certain jurisdictions. HF communications also occur over open, well-advertised frequencies and, unlike VHF, general purpose shortwave radios often have the frequency range to tune into oceanic ATC. Due to the nature of HF propagation, it may be possible to listen to controllers thousands of miles away, but the reception quality will vary.
The ADS-B system, as it operates currently, is an open system as well. It is possible to purchase an ADS-B receiver for as little as $600. A number of enthusiast sites such as flightradar24 (Scandinavian region), Zurich University of Applied Sciences’ School of Engineering radar site (Switzerland) and Casper(Netherlands) provide an overview of aircraft in their region by listening to ADS-B transmissions.
References/Further Reading
Aeronautical Radio Communication Systems and Networks – Dale Stacey (ISBN: 978-0470018590)
Avionics: Elements, Software and Functions – Cary R. Spitzer (ISBN: 978-0849384387)
Skybrary
ATC Monitor
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About the Author:
The author is an Air Traffic Controller, Aircraft Accident Investigator and Aviation Safety Specialist. An Aircraft and Helicopter Pilot.
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About the Author:
hope it can help you more or less!
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