The Magic of the Aircraft Trajectory

On 22/04/2013, in Buzzwords explained, by steve

photo_bluskyTrajectory based operations or TBO figure frequently in current air traffic management related concept documents and discussions. When asked, most experts will say that they understand what TBO is… but scratch the surface a little and you will find that at best they all have a different understanding and at worst a completely wrong understanding of what TBO really means.

I am not going to bore you with yet another discourse on TBO, I have written more than enough on the subject already. This time I would like to hold a magnifying glass over the trajectory itself and give you what may prove to be a rather unorthodox view of this ever present yet ethereal thing that has many more uses than one would think on first sight.

As we know, trajectory based operations, at its simplest, means going away from the legacy airspace based air traffic management paradigm to replace it with a trajectory based one. In the legacy approach, experts try to guess the dimensions of the airspace required to accommodate the traffic demand and then force aircraft left, right and centre to fly in ways that fit the airspace. What is more, controllers focus on the aircraft with minimum look ahead times to discover and resolve conflicts. It is little wonder that aircraft often end up flying trajectories that have little resemblance to what the airspace user originally intended.

Under trajectory based operations, airspace is designed to accommodate the trajectories without distortions whenever possible and controllers consider the impact of their actions on the entire trajectory still to be flown. With appropriate decision support tools, they select intervention options that result in the least overall distortion of the trajectories concerned.

But what is this trajectory we are so often talking about? One possible definition of the trajectory is the series of points on the ground and in the air that describe the path the aircraft will follow. These points are not navigation aids but rather the kind of points we know from geometry; by connecting the points we get a visual representation of the path the aircraft will follow. We can identify any point on this path by its three spatial dimensions and the fourth dimension, time. This is how we come to know where the aircraft will be and when.

Some seem to think that a trajectory is from gate to gate only and there is no such thing as a trajectory during the turnaround. Here is then the first opportunity to consider the trajectory in a new light.

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European Air Traffic Management – A historic clash of concept and politics

On 05/07/2012, in SESAR's Palace, by steve

Although you would never know it from reading the rather upbeat communications from the Functional Airspace Block (FAB) and SESAR folks, ATM in Europe is heading towards some major turbulence. That the EC’s Single Sky Committee very nearly managed to kick the deadline of meeting the Single Sky (SES) high-level goals a further 13 years into the future (to 2033!!!) is only one indication of how the whole structure is creaking under the relentless drive of the backward thinkers hell bent on keeping things from happening.

But there is more. What about a collision between a black hole and a complete galaxy? Astronomers amongst you will say this means complete annihilation for the galaxy. Now replace black hole with FAB and the galaxy with SESAR. I am not kidding!

Various high level managers at the European air traffic management organizations hasten to point out that SESAR has always been envisaged as being based on the FAB idea, that they are completely compatible with each other. Quite apart from the not negligible fact that this is simply not true, such claims also show just how little some people seem to understand the difference between the FAB idea and what SESAR represents.

What SESAR is aiming to introduce is a set of paradigm changing concepts, among them Trajectory Based Operations (TBO). I will not go into the details of TBO in this article, if you are interested, read more about it here and here. Let it suffice to say that we left out any mention of FABs in the original SESAR concept of operations for a very good reason. The kind of fragmentation represented by the FABs is not only not needed under the TBO environment of SESAR, it is a hindrance that can potentially kill any hope for true TBO.

What are the Functional Airspace Blocks or FABs? They are most certainly not an air traffic management concept or method of working or even an idea that would make things work better by definition. FABs are in fact a sad admission that Europe did not succeed in creating a continent-wide air traffic management environment that would have come anywhere near satisfying the users’ needs. So, in order to make a little progress, some poor soul somewhere came up with what might appear to be a pragmatic approach. If Europe’s Air Navigation Service Providers as a whole cannot be made to work together properly, lets beat them into a few small groups, focused around newly defined blocks of airspace that have similar user requirements in the hope that these groupings will be more effective in working together in a sensible way.

So, for starters, FABs are not an ATM concept but a political construct aimed at getting the ANSPs to cooperate properly at least on a group by group basis.

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Effective Data Communications for NextGen

On 09/05/2012, in NextGen, by mike@boeing

Beneficial Capabilities

Air traffic service (ATS) data communications provide benefits in terms of increased airspace capacity and improved operational efficiency while also enhancing the existing high level of safety.

Increased airspace capacity. In continental/domestic airspace, capacity is primarily increased through basic controller-pilot datalink communications (CPDLC) that reduce controller and flight crew workload as well as voice frequency congestion associated with routine communications. More specifically, basic CPDLC offers information exchange between the controller and flight crew for vertical, crossing constraint, lateral offset, simple route modification, and speed change clearance request and delivery. Effective strategic management of predictable and accurate aircraft trajectories in the future is also expected to increase continental/domestic airspace capacity; for example, delays due to convective weather will be mitigated by the ability to quickly supply complex route modifications to a large set of affected aircraft before departure. In oceanic, polar, and remote airspace, capacity is primarily increased through manual and automated reports that enable reduced aircraft separation by reliably providing surveillance data for separation assurance, flight plan conformance monitoring, and trajectory planning purposes.

Figure 1. Dynamic Airborne Reroute Procedure

Improved operational efficiency. Operational efficiency is primarily improved through trajectory-based operations (TBO) that decrease aircraft fuel consumption and/or flight time, particularly in the face of constraints that would otherwise increase those parameters. Parallel integration of ATS provider ground automation, aircraft operator ground automation, and avionics (aircraft automation) and of controller, dispatcher, and flight crew operations enable TBO for rapid and accurate trajectory definition, coordination, and monitoring. TBO can be used, for example, to reduce flight time through user-preferred complex route modifications for in-flight aircraft as seen with Dynamic Airborne Reroute Procedures (see Figure 1) and to perform environmentally-friendly fuel-saving optimized profile descents as demonstrated by Tailored Arrivals (see Figure 2).

Figure 2. Tailored Arrival

Enhanced safety. Safety is primarily enhanced through accurate machine-to-machine exchange of precise data, such as complete three- or four-dimensional complex routes and latitude/longitude coordinates that resolve duplicate waypoint identifiers. These exchanges prevent gross navigational errors that could otherwise be caused by the flight crew manually transcribing detailed information.

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Aircraft turnaround made visible from a TBO/SOA perspective

On 29/04/2011, in Buzzwords explained, by steve

Trajectory Based Operations (TBO) and Service Oriented Architecture (SOA) are two concepts rather new to air traffic management (ATM) and apparently they continue to cause some head scratching when it comes to agreeing what TBO really means or how to define services in the ATM context. In this article I will attempt to explain a few relevant aspects of those concepts and will also try to visualize the concepts using the aircraft turnaround as an example.

Why the aircraft turnaround? Because we see that in spite of the original SESAR Concept of Operations having made clear that the trajectories of flights performed by the same aircraft are in fact always connected via the given airframe, some experts are now laboring to show that this is so and are trying to bring in new constructs to account for this “connection”. The trajectory does go through important metamorphoses during the turnaround and so using that phase of the operation gives us the opportunity to examine TBO and SOA in all their glory.
But first a few basics.

The concept of services.

“Service” is a word that can mean different things depending upon the context in which it is being used. In general, the context is based upon a consumer/supplier relationship. Further, a hierarchy of services can exist with, for example, a high-level service being made up of a number of lower level sub-categories of services. Therefore, it is very important to ensure that the nature, scope and detailed characteristics associated with each service are clear and unambiguous each time it is used, including defining who is supplying what to whom.

Services may be defined from a business perspective or an IT perspective.

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Do you really understand – Trajectory based operations (TBO)?

On 04/02/2011, in Buzzwords explained, by steve

There is a misconception in some air traffic management circles that trajectory based operations is simply business as usual except that the current, notoriously imprecise ground generated trajectories are replaced by more accurate, 4 D trajectories and that is all there is to it. Some will add that parts of this 4D trajectory might be sourced from the FMS or an airspace user ground system… While there is truth in all this, TBO is much more. Much much more and significantly, if the other aspects of TBO are not considered, the potential for benefits inherent in TBO is reduced significantly.

So, what is trajectory based operations?

First and foremost we must look at the basis of the existing operation. Air traffic management has grown historically along an airspace based paradigm. Airspace as such was a given so it stood to reason that early ATM experts set out to define airspace volumes which they thought would best fit the traffic they expected and established air traffic control units to fit the task foreseen in those volumes. When aircraft arrived, they were obliged to fly within the confines of the defined airspace and if their needs differed from that envisaged, the aircraft trajectory was bent to fit the picture. Of course this is a bit of an oversimplification but to this day, ATM is being done on this basis.

The end-to-end trajectory played almost no role in this game. To illustrate the point, juts consider that until recently the Central Flow Management Unit calculated expected sector loads on the basis of a trajectory the vertical dimension of which was famously inaccurate while ground ATC systems generated their own trajectories for their own airspace and these often did not tie up with the trajectory dreamed up by the neighboring unit. All this time however scores of experts everywhere worked furiously on airspace design and organization… Only a blind person could fail to see that this legacy, airspace based paradigm had to go if the volume and efficiency demands of increasing traffic were to be met.

Things were not helped at all by the fact that controllers were handing flights as if they were born just outside their sector boundary and went into the big blue yonder when they exited their sector. In other words, they only ever looked at a small part of the trajectory with little regard to what was or was not happening further downstream. Conflict free handover was the almost the only aim.

Because of the way airspace was used in the past, popular ATM wisdom came up with the notion that airspace was a scarce resource and it had to be organized better to save the day. This notion was a dangerous one because for a long time it did divert attention and effort from looking at the real problem. Trajectories…

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Trajectory based operations (TBO) – Still not properly understood in SESAR? Take 2.

On 18/01/2011, in SESAR's Palace, by steve

You may recall that a while ago I had written an article with the same title, expressing concern that this all important element in the SESAR Concept of Operations was apparently still not properly understood by some of the “experts” working on the subject.

Recently another paper dealing with trajectory management crossed my desk and on reading it I started to wonder: have these people not read the CONOPS at all? Mind you, the paper comes from a major SESAR partner who should know better… But apparently they do not.

The paper is entitled “Use of the SESAR RBT in ATM Systems”. RBT in case you did not know stands for Reference Business Trajectory and this is the trajectory that “the airspace user agrees to fly and the ANSP agrees to facilitate” to quote the relevant part of the SESAR Concept of Operations (CONOPS).

The purpose of the paper, by its own admission, is to prompt discussion of the trajectory issues within the SESAR program and in particular to ensure that they are addressed by Work Package B. In other words, the paper is arguing that alongside the RBT, the various other types of trajectories that exist in local systems must also be recognized and treated in SESAR. Since the CONOPS already contains references to all those “other” kinds of trajectories, one cannot but wonder: what do the authors of the paper have in mind? Why would SESAR ignore the CONOPS references to those other trajectories? Or have the authors not read the CONOPS and are now thinking that they have discovered a gap in that document?

I will not even attempt to figure out this aspect. There are many other elements in the paper that should make anyone familiar with trajectory based operations want to cry.

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Functional Airspace Blocks (FAB) – New category on Roger-Wilco

On 03/01/2011, in FAB News, by steve

FABs may be the highest political priority for the European Commission and they certainly are the source of high flying political statements, but I still do not like them. Why? Well, the idea when it first came up was a good one. At the time, functional fragmentation of air traffic management in Europe was costing airspace users billions and in spite of all the projects being considered, there was little hope for structural reform.

In order to break the logjam, and fully aware that there was no hope for getting the whole of Europe to co-operate and create a single sky, the EC very pragmatically proposed that groups of States get together and create functional airspace blocks (FAB) along the lines of their ATM “interests”, optimizing and aligning procedures and services inside their FAB… This way, the argument went, at least there would be a single sky of sorts inside the FAB and later on the FABs themselves could be harmonized for a truly single European sky.

Pragmatic and logical as the idea may have been, it was not received by the ANSPs with open arms.

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Trajectory based operations (TBO) – still not properly understood in SESAR?

On 26/11/2010, in SESAR's Palace, by steve

Following Henning’s article about the fate of the original SESAR Concept of Operations (CONOPS), I received a slew of mails basically confirming his point of view and worries. Of particular concern seems to have been a document dealing with trajectory management…

People who had seen this document were of the opinion that it was little more than a reiteration of the legacy way of working with no visible attempt to bring things in line with the spirit, let alone the words, of the CONOPS.

Why am I not surprised?

During the definition phase we had a very hard time getting people to understand why the legacy system, based on managing airspace and massaging individual aircraft left and right had to give way to something else that took a broader view than is the event horizon of a controller working his or her sector.

The concept of trajectory based operations (one of the mainstays of NextGen also) does exactly that. The system is run on the basis of managing trajectories end to end with situational awareness shared by all concerned and hence both strategic and tactical decisions being aligned, safety permitting, with the business intentions of the owners of the trajectories. Airspace is shaped to allow the undistorted inclusion of the trajectories rather than trajectories being bent to fit the airspace.

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Performance Based Navigation (PBN) – Why the “N” should be an “O”

On 11/03/2010, in Buzzwords explained, by steve

The abbreviations game

In aviation we seem to be creating abbreviations at a rate that raises the specter of our grandchildren not having any usable combinations left any more. This remark from a well respected colleague of mine who used to work for UPS airlines does in fact indicate a few problems that go beyond the scarcity of available unique letter combinations and which, as we will see, affect our daily work in all kinds of unexpected ways.

This is not aviation CNS...

Consider the well known CNS formation which, we all know, stands for Communications, Navigation and Surveillance. Whoever came up with the abbreviation CNS probably had no idea how much damage their invention would cause in air traffic management by perpetuating the kind of silo mentality that keeps many organizations hopelessly divided and some experts retreating into their respective ivory towers.

If at least the inventors had the good sense of putting those letters into some kind of logical order, like history, which would have given us NCS… We did navigate first (as in trying to find our way by reading the names of train stations and flying along highways), then communicated, initially with lights and hand signals and later via radio and most recently we do surveillance also. Not that NCS would have been any better at driving the silo mentality from the face of the earth.

Of course in the old days there was some logic in looking at navigating and communicating as something totally different from each other. You trained for one or the other, aircraft carried separate navigators and radio operators and when radar came along, the wizards of that kit were a completely new breed yet again. It was only logical also that separate fiefdoms should grow up along the letters NCS with hardly any horizontal contact between them. That they should fiercely protect their respective domains was perfectly natural…

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Is the industry ready for this?

On 19/01/2010, in Environment - Without hot air, by steve

The northern hemisphere has just gone through its snowiest January days in 40 years and polar temperatures reached as far South as Orlando in Florida. Sure, this is not abnormal some may say… but what if we do not have to wait forty years for the next episode?

An Air France flight en-route from Brazil to France encountered so severe turbulence that they issued a Mayday call but subsequently they completed the flight without incident. As we all know, AF447 was less fortunate.

Over the past 18 month or so, there were several incidents where unexpected severe turbulence caused passenger injuries…

And now the European Aviation Safety Agency (EASA) says, as reported in Aviation Week, that “climate change could be contributing to more extreme weather conditions at high altitudes that have not previously been encountered by aircraft”.

Make no mistake, although the current investigation of the crash of AF447 talks a lot about the problems with pitot tubes prone to freezing, there is a much more sinister implication here. Pilots are trained to handle situations where pitot tube data is lost or is unreliable… You cannot however train pilots to fly an aircraft with a wing or stabilizer gone. This is the point… who says extreme weather can only come in the form of extreme cold and not also as extreme turbulence?

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