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Standing By For Amended Clearance:
FAA Moves ADS-B- WAAS- NextGen.


In Alaska- pilots started seeing the benefits years ago; ditto for UPS aircraft crew once they entered the airspace of Indianapolis Center headed for the shipping giant’s main air hub at Louisville International Airport (SDF). Then- more than a year ago- appropriately equipped pilots flying through South Florida may have seen and used it. Early this year- pilots flying about one third of the helicopters servicing off-shore energy-production platforms in the Gulf of Mexico most assuredly gained the advantages of this beneficial technology. And in March the system came on-line for the airspace around Philadelphia.

We are- of course- talking about Automatic Dependent Surveillance-Broadcast (ADS-B). ADS-B is spreading steadily across the airspace system as the technology the FAA plans as the foundation of the Next Generation Air Traffic Management System. NextGen- as it’s colloquially called- is actually the FAA’s $20 billion package of multiple inter-woven projects designed to reinvent both the technologies used to track- guide and manage aircraft and revise procedures and practices to exploit the benefits and gains of the new technologies.

The nation’s aviation community and its regulator/proponent have for more than a decade already been engaged in research and development to advance the change-over. If the FAA gets its requested funding- $1.14 billion will go toward the project in Fiscal 2011 alone – about one-third more than in the current year and a mark of how the project continues to gain momentum- even though it is already somewhat behind schedule.

TEST BEDS BEGET BEST BETS
Beyond Alaska and UPS- general and commercial aviation operators long ago began embracing another element of this vast overhaul of ATC technology and flow management: the Wide Area Augmentation System (WAAS)- and the Multifunction Display (MFD).

In the past few years- avionics makers began adapting WAAS capabilities into a broad spectrum of GPS navigators- from humble hand-held navigators popular as back-up solutions through to the most-expensive IFR-approved panel-mounted systems common in today’s business aircraft panels.

Out in the commercial-flying world- the regional carrier Horizon Air became the first FAR Part 121 passenger airline to adopt WAAS technology- launching WAAS-supported service after installing new FMS hardware in its fleet of Bombardier Q-400 turboprops. Fitting its aircraft with new UNS-1EW WAAS Flight Management Systems was not an inexpensive decision. But in line with the long-held philosophy of its parent- Alaska Airlines- Horizon looked at its operating environment and made a decision that favors its performance and its passengers.

Not long after Alaska’s action- Southwest Airlines announced it would be using the WAAS GPS technology to shorten routes- save time – and by extension fuel – and save money…on top of the approach benefits. And so it is for this landmark overhaul of the nation’s ATC system: While the costs are significant- the nation- the FAA- commercial and private operators are in a rare convergence of opinions - the changeover must happen to allow aviation to grow- traffic delays to fall- and to provide maximum distribution of the economic benefits of access to the national air-transportation system.

THE BASIC IDEA
Down the decades- companies named Bendix and Collins invented instruments that helped pilots fly “blind” in and above the clouds and stay oriented- straight-and-level day and night- while others invented ways to navigate by radio beacon – and then to track and locate aircraft by bouncing radio waves off them.

From tracking to the known position of high-power broadcast radio stations like WLS- WNBC or WHAS- to listening to the four-way radio range and- finally- the Omni- Directional Beacon- or VOR- and then the Distance Measuring Equipment (DME) enhancement and the long-range area-navigation of Loran C- aerial navigation has remained decidedly ground-based.

That started changing only in the past 20 years- as GPS reached a level of maturity to make it available around the globe 24-seven- 52 weeks a year. Tracking- however- remains solely a ground-based proposition- one enhanced in the past 50 years by the advent of the radar transponder and- in the past 35 years- altitude reporting capability for the airborne equipment.

Controllers today use radar that still depends on a return signal to help measure distance and direction from the antenna – but with modern Mode A- Mode C and Mode S transponders and Secondary Surveillance Radar- what the radar system processes is actually a signal sent by the transponder in the airplane – with that signal carrying a four-digit code to help controllers identify and process multiple aircraft- plus an altitude code showing the aircraft’s pressure altitude as detected by the on-board system.

Through powerful computers processing thousands of messages a second- the nation’s controllers can track the tens of thousands of flights they work daily- and keep them separated and flowing through a four-dimensional system- one working on latitude- longitude- altitude and time.

Great as this is- however- the individual errors and shortcomings of these different systems compound in a way that constrains how effectively the controllers and all their skills can use the airspace. Radar antennae monitoring the en route environment rotate only once every couple of minutes; an airplane moving even as slowly as a piston airplane can cover several miles in that time – a high-speed propjet or jet many times more. And the radar data itself is not pinpoint accurate to start; compound the inherent position error with the time factor and you find yourself at the foundation of some of the FAA’s horizontal-separation requirements.

The altitude information itself is only as accurate as the device sensing the air pressure. The controller must set a translating altimeter setting for the computer to translate the altitude code of a transponder “squawk” into an altitude readable on the screen. If actual conditions at the point of flight differ slightly from the correction setting used- the aircraft may be off many feet from the reported altitude… and now we can see the basis for the FAA’s altitude-separation regulations.

Thanks to the magic of GPS- the accuracy wonders of WAAS- and a technology bridging the aircraft’s ability to participate its position reporting called ADS-B- controllers are already moving into a world where the accuracy of information on their screens falls not in miles or hundreds of feet – but in a meter or two- laterally and vertically.

Working together in a seamless network is the goal – the hardware of a system called NextGen. And the update cycles happen hundreds of times a minute – meaning that positional information is always only fractions of a second old- an important factor for aircraft often moving at close to 600 miles per hour.

ADS-B GOES LIVE IN PHILADELPHIA
Pilots of properly equipped aircraft flying through the Philadelphia area can get a glimpse of the future of flight now that ADSB service has been switched on there. The FAA activated the system on February 26- but didn't announce it immediately. Aircraft with a universal access transceiver (UAT) can display weather and aeronautical information on their cockpit displays- as well as traffic advisories.

Those with a 1090 MHz Extended Squitter (1090ES) can only get the traffic. The FAA is warning that the information available is advisory only and not a substitute for official sources of weather and NOTAMs or looking out the window.

An FAA NPRM for ADS-B also envisioned using something called a ‘Universal Access Transceiver’ – essentially a device that performs the same functions as 1090ES- but with the added benefits of providing channels that allow appropriately equipped airplanes to also receive and display independent information on traffic and long-range weather.

Like any new and complex system- there are bound to be bugs- and the FAA is hoping pilots will pay special attention to the functionality of the system and report any problems. ADS-B is the foundation technology of the NextGen airspace modernization program.

HESITATION POINTS
Avionics manufacturers- in the meantime- still hesitate because of doubts and concerns; the concerns about which type of ADS-B technology (or technologies) will win out with the FAA and- in turn- whether efforts invested in today will have a resulting payout in the future.

The UAT offers low-costs and access to the Flight Information System of weather data and the Traffic Information Service for tracking traffic via a link based on this type of ADS-B technology. One UAT offers benefits unavailable via the other; one offers costs breaks not available in the other - and both can satisfy the needs of the program- one avionics-maker executively told World Aircraft Sales Magazine during a conversation at the recent Aircraft Electronics Association Convention.

The 1090ES has the benefits of being accepted in other markets overseas- the other UAT- the benefits of added services to pilots. Adding to the confusion and the dilemma is the FAA’s proposal to use both technologies- and hardware and software to translate both signals into something useable by ATC.

“Developing a new piece of hardware from inception to final TSO can take three or more years-” said one avionics company executive. “My bosses want to make sure there’s at least a potential payoff before putting their efforts behind either – or both. Nobody in this business wants to engage in an effort with no hope for a payback. This is not today’s MLS- and we’re not cooking with it…”

FAA STAFFER
Among the hesitation factors for avionics-makers and pilots alike are memories of the early-to-mid 1980s- when the FAA embarked on development of a technology known as the Microwave Landing System (MLS).

MLS- as it was colloquially known- had nothing to do with cooking or heating food and everything to do with providing a three-dimensional area-nav-like solution to replace and enhance the system used until today for landing reference in IMC: the Instrument Landing System (ILS). MLS ground stations could guide MLS-equipped aircraft through a three-dimensional curving approach to a precision-level landing – all while the aircraft operated with near zero-zero ceiling and visibility.

Unfortunately- factors combined and conspired to thwart the goals of MLS and the future of the technology – despite extremely successful testing and demonstrating. The airborne boxes – in prototype form- predominantly – were prohibitively expensive- the ground systems high-dollar- and the people willing to invest at near zero.

“Nobody who remembers those days wants to endure another MLS experience-” another avionics company staffer told us. “MLS had great potential and excellent performance – it just cost too much and offered too little gain for the money…in other words- the juice wasn’t worth the squeeze.”

But major differences exist between MLS and ADS-B - among them early prototyping- resulting early proving trials; and much lower costs to both the public and private enterprises engaged in moving ADS-B down the road. With years of tests proving the benefits- with thousands of hours flown demonstrating the events- and with tens of thousands of dollars that ADS-B doesn’t cost by comparison to MLS- even the off-route benefits seem secure. And with the FAA creating several hundred new LPV approaches each year- the potential for reaping the benefits of ADS-B seem strong.

SHARPENING GPS ACCURACY TO A PINPOINT
If you’ll allow the analogy- WAAS gives GPS corrective lenses on a par with anything an ophthalmologist might fit for a common case of astigmatism – a distortion of human vision caused by an irregularity in the cornea.

In the case of the GPS system- the signals from satellites orbiting 22-000 miles up suffer from some distortion caused by the Earth’s atmosphere and the time lag between the signal leaving the airplane and it being processed by the positioning receiver.

WAAS uses a wide-area network of precisely sited ground stations to monitor those sources of inaccuracy and broadcast a corrected signal through special satellites in the GPS constellation. By knowing within inches their exact location- the ground stations can compare their translation of satellite signals and correct the signal errors that produced the error derived from the non-WAAS GPS signals. And the ground stations and WAAS satellites can perform this correction hundreds of times a minute.

The WAAS ground stations have been in place and functioning for several years- and today- GPS users use their receivers with WAAS built in- gaining all the accuracy benefits that in aircraft uses are to within a meter.

Without WAAS- the other leg in NextGen- ADS-B- would improve over today’s radar-and-transponder-dependent system – but not by enough to warrant the billions being spent in the transition.

HERE’S WHERE IT GETS REALLY GOOD
Under ADS-B- participating aircraft produce their own position information and share it with the ATC network – and other aircraft (if those aircraft are equipped to benefit). An ADS-B-compliant aircraft will- at a minimum- need to have a TSO-compliant WAAS GPS navigator and a way to broadcast the navigator’s information. And that information- for starters- includes not only within-a-meter-accurate position data- but accurate altitude- speed and flight-direction information.

Another aircraft equipped to receive ADS-B broadcasts would be able to pick up the report of any participating aircraft within range (about 150 miles) and show that aircraft on a cockpit MFD. A national network of ground stations- more than 200 overall- is designed to receive aircraft ADS-B broadcast reports and channel them to show up on ATC screens – and re-broadcast them so aircraft with different types of ADS-B reporting technologies can all see and hear one another. Again- this reporting and sharing of position information occurs hundreds of times a minute.

The extreme accuracy of the ADS-B information – including the WAAS GPS position information- speed- altitude and direction – mean that controllers will be able to safely monitor and manage aircraft without wasting as much airspace. Instead of 10 and 20 miles (and more) between aircraft- the system can work at 1-- 3- and 5-mile levels- knowing that their information is accurate.

And from this ability to shrink separation standards – bad weather as well as good – the airspace system can accommodate more traffic. More planes operating to more locations with greater safety margins – who in the industry is going to argue with that?

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