SBAS, GBAS – What is this? The technical aspects.

On 28/05/2014, in Buzzwords explained, by steve

Those who are familiar with approach procedures feel free to skip this post… I am not going to disclose anything new ore revolutionary. However, with Performance Based Navigation (PBN) and as part of it, GPS based approach procedures become more and more common, I thought it a good idea to summarize what a Space Based Augmentation System (SBAS) and a Ground Based Augmentation System (GBAS) is, what they are used for and why they are required at all. I think there are readers out there who have not dug themsevles into the mysteries of satellite based navigation and for them a bit of background knowledge might come handy.

To understand the issue at hand, first we need to go back to our well known and well trusted current approach and landing aid, ILS (Instrument Landing System). ILS provides precision vertical and horizontal guidance to aircraft on final approach to a runway. The system can provide this guidance with three distinct levels or Categories as they are called. CAT 1 means that the pilot may descend on the ILS glideslope to a minimum of 200 feet above the runway where he must have the runway in sight visually and if not, he must initiate a go-around. The same minimum is 100 feet for CAT II. CAT three has not vertical limit and only a certain Runway Visual Range (RVR) must exist for aircraft to land (usually in full automatic mode).

ILS is relatively expensive to buy and deploy and its cost of ownership is also substantial, not least because of the need to fly regular calibration flights checking out the system every year. Another shortcoming is that when the weather really socks in and CAT II/III landing operations are in progress, departing aircraft need to hold relatively far from the runway to avoid interference with the radio signals. This has a marked negative effect on the departure rate of an airport. Finally, but not insignificantly, you need a separate ILS installation for each runway end to be served.

With the availability of the Global Positioning System (GPS) came the realization that it should be possible to use GPS also for final approach guidance. A lot of advantages were immediately visible. One could define an instrument approach procedure basically anywhere, even when there was no runway… or conversely, approach procedures could be developed for each runway end for all the runways at an airport without having to deploy anything o the ground. And aircraft equipped to use the GPS system was, in principle, already able to fly a GPS approach. The beauty of such a solution is also that the long, straight final track of the ILS could be replaced by a curved track if required for, as an example, avoiding noise sensitive areas or wildlife preserves or whatever. A straight track was required only in as much as the aircraft needed it to be able to set up a stabilized approach.

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Don Quixote in the windmill

On 25/05/2014, in Tower chronicles, by lajos

don_qioxoteAfter a long and arduous battle, Don Quixote, the brave knight has finally managed to conquer the windmills! Walking on foot towards the door of the windmill he was running a mental exercise listing all the things he would be doing in there. He has been dreaming about this for years, how he will save the world once inside the mill, how he will mill the flour which will be much finer than anyone had ever created before. That his flour will be liked by everyone he doubted not at all. With a drop of tear in his eyes he looked once more at the conquered wings of the mill. Almost regretting that the battle was over, our knight stepped to the door opening it bravely. Well, life goes on and us, with it.

Don Quixote had often pictured the insides of the mill, imagining all the nice, pleasant and interesting things lurking there, always adding a thought about how he will enjoy himself once on the other side of that door.

Stepping through the door the first obstacle reared in the form of two mean looking guards who blocked his way. Our hero did not bat an eye… after all, he had fought with such characters thousands of times before at the fence guarding the windmill. To his surprise when he grabbed for his sword, the guards started to smile and greeted him politely. Our knight was a bit confused but he said hello and started to walk again, stealing a look backwards to make sure the guards did not pull a fast one and attack him from behind. But they were ignoring him already, once again fixing their gaze on the door. This surprise was followed by the second, close upon the heels of the first. Don Quixote had no idea so many people were working in the mill. Strangers were passing him left and right going after their business without casting him a glace. Are they all millers, our hero wondered in amazement. They all appeared to be much younger than himself and this only added to his confusion.

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Up close and personal – Mind games with the aircraft trajectory

On 24/05/2014, in Buzzwords explained, by steve

060504_091043The term “trajectory” does not need an introduction to pilots and air traffic controllers. At its simplest, trajectory to the pilot is what the aircraft flies and to the controller the path through the air calculated by his or her system that the aircraft will fly. Hence it is fair to say that if we define trajectory as the series of points in space that the aircraft will occupy as it proceeds to its destination, we are not far from the truth.

In the traditional scheme if things air traffic controllers were looking at a small section of the trajectories, may be something like 10-20 minutes into the future, and moved aircraft around as necessary to avoid conflicts. In other words, they were managing aircraft, not the trajectories.

When the concept of air traffic flow management (ATFM) was defined, we did take the first step towards what is to-day known as Trajectory Based Operations (TBO). After all, ATFM was trying to predict what would be happening in the airspace hours or even months ahead in order to ensure that the resources necessary to handle the demand were made available on a timely basis (or that demand was capped but that is another story).

TBO came into its element when people finally realized that traffic demand expected around the turn of the century would no longer be manageable using traditional methods. The need to switch from managing aircraft to managing trajectories became clear.

If aircraft fly precisely defined trajectories that are described in the three spatial dimensions as well as the time dimension, by managing the trajectories on a timely basis one could make far better use of the available capacity in the airspace while avoiding an overload of the human controllers also. Simulations have shown conclusively the fallacy of the oft repeated argument that airspace was a finite resource… No, airspace appeared to be a finite resource only because of the way it was being used. Managing trajectories unlocks the inherent capacity of the airspace in a safe and efficient manner.

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Apropos GATE ONE… Is there hope for European Air Traffic Management?

On 22/05/2014, in FAB News, by steve

trylThe fragmented nature of the way air traffic management was being provided in Europe had been identified decades ago as the root cause of the continent’s problems. This is why airlines are paying much more for inferior service and why repeated attempts were made to remedy the situation.

This being Europe, the real issues were never addressed. It would have been political suicide for anyone to suggest that may be, just may be the opposite of fragmentation is united, uniform, single, optimized, right-sized… Make no mistake, some of these words have been brandished around lately, as in Single European Sky… but in practice they were meaningless.

Instead of finally getting to the point where EUROCONTROL would have been developed to be THE European organization to provide efficient air traffic management, European states managed to set in motion a process that has two effects: EUROCONTROL is doomed to die and the fragmentation of ATM in Europe is set to grow to levels never before seen.

It is unfortunate that the European Commission, correctly recognizing that the existing system did not work, has not had the good sense to also recognize that the problem was not EUROCONTROL, but the way member states were behaving as part of that organization. Being blind to the real problem, the EC went down the dead-end street of the Functional Airspace Blocks (FAB) in the mistaken belief that if Europe could not be brought to work together as a whole, it would be different if things were handled in chunks… FABs in other words.

So, instead of reducing fragmentation, they increased it and what do we find? Surprise, surprise, the FABs (those that exist at all) are facing the same problems and are failing in most of the same ways, as Europe did in the past.

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PNT and RNT. What are these?

On 01/05/2014, in Buzzwords explained, by steve

gpsPNT stands for Positioning, Navigation and Timing and in most cases it refers to the signals from the satellite constellations we know as GPS, Glonass, Galileo or their regional equivalents in India, China and Japan. These days we take it for granted that our smart phones, cars, tablets and so on include a small receiver that can make use of the faint signals from those constellations to tell us where we are. Aircraft in turn use the signals to fly ultra-precise approaches. This is important but for the world at large, even more important is the precise timing that the satellites make possible. Power grids, the cellphone system and other important systems make use of GPS time to operate. Without this timing, the systems would collapse.

You would think that with something as important as the PNT signals, they would be protected from malicious intent. In fact, the signals are totally unprotected. With a box costing just a few hundred euros or even less, it is possible to block GPS signal reception in a substantial area, causing havoc to even safety of life systems. Sometimes you do not even need malicious intent as was demonstrated by the GPS jammers installed in trucks in the US to keep the boss from learning where the vehicle was on the road… Newark Liberty airport has a highway quite close to the runways and the jammers made GPS unusable also for aircraft whenever a truck passed nearby.

Experts have been saying for years that putting all of aviation’s eggs into a single basket called GPS was a bad idea but the prospect of a cheap and efficient system was too much to resist and PNT signals are fast becoming indispensable to aviation.

It is a wonder that no bad guys have yet come to the conclusion that they do not need to blow things up to cause untold economic damage to a country they have a gripe with…

What can be done?

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Quote of May

On 01/05/2014, in Quote of the month, by steve

A successful man is one who can lay a firm foundation with the bricks that others throw at him.

Sidney Greenberg

brick

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