A Short (Unofficial) History of The Air and Ground Digital Link - Finally All on Board
Pioneers to the rescue In spite of the positive business case, airspace users were not exactly rushing to equip with air/ground digital link.
Because of the slow down of traffic growth in the wake of 9/11, the expected ACARS problems did not materialize and the ATC frequency congestion was also pushed far into the future.
In other industries, such a period of respite might have been used to prepare for the times when business recovery would once again make air//ground digital link essential.
But that is not how aviation works.
With the immediate threat receding and even some of the big carriers fighting for survival, enthusiasm for investing in things that would generate benefits only many years down the road cooled.
Of course for the planners of the ATM system this was a situation that spelled trouble for later.
The frequency congestion problems were not a mirage even if for the time being those problems slipped into the future.
The need to put together a comprehensive kit of capacity enablers had not become less important, only the urgency had changed somewhat.
For LINK2000+ the big question was: how to jump start equipage? The question was not self serving at all.
If Maastricht UAC controllers did not get digital link equipped aircraft to work with, it would be impossible to build and maintain proficiency and to shake down the system in real operational circumstances.
The solution was simple...
money.
A proposal was put forward to EUROCONTROL that called for a set of pioneer airlines who would get (part of) their initial investment paid and they would then form the core of equipped aircraft in the hope that after a time others would also follow as the potential benefits came near in the bean counter calendars.
The "pioneer" idea was a big success and LINK2000+ managed to line up an impressive number of airlines and aircraft.
What was never said openly was of course the fact that the pioneer airline success was also a clear demonstration of how effective a bit of infrastructure help can be in solving air traffic management problems.
Politicians shooting from the hip take note...
Finally all on board Of course in time also Airbus came on board as did the other airframe manufacturers before them.
Air/ground digital link became recognized as one of the premier capacity enablers in both SESAR and NextGen and air navigation service providers across Europe are working on their implementation programs.
The question is now not if, but when.
It is easy to make the mistake and think of air/ground digital link as something we need only in congested airspace.
After all, where there is no congestion the frequencies will not be congested either, so why spend money on digital link? There is some truth in this but on the other hand, if a pilot has to fly across the continent and keep switching between voice and text messages, the situation might very well become untenable from a safety point of view.
Operational uniformity has its advantages and the biggest investment is on the aircraft so why not use it everywhere? This idea of universal digital kink usage is sometimes countered by the airspace users saying that voice is free while digital link usage carries a price tag...
Well, voice is not free.
Has never been.
Is the use of the ILS or the VOR free? Of course not! The costs of voice are simply "hidden" in the charges in general while the cost of digital link usage is (in part) payable by the airspace users.
The important aim must be to ensure that there is no double charging...
Who uses digital link should pay for that and that alone...
Digital link...
for non-time critical messages only? In the early days of digital link usage, the greatest worry was the time it would take for messages to get from the controller to the aircraft and vice versa.
This worry was fuelled in no small measure by the perception by controllers that voice is faster than digital link.
What was often forgotten was the parallel versus sequential nature of digital link and voice, respectively.
A lot was made of message transit times and very little talked about actual communications speed.
Very rare, extreme cases apart, the digital link message transit times end to end are measured in a few seconds or, more commonly, in fractions of a second.
Compared to the "instantaneous" contact voice seems to make possible, this is indeed a "long" time.
Voice does not have a message transit time on the VHF AM radio...
But if we look at the communications speed in a congested voice environment, we get a very different picture.
The moment the controllers decides that he or she has a message to send, the frequency may not be free...
so they wait.
Then they start talking but the receiving aircraft may or may not be able to acknowledge right away because of the same frequency congestion problem.
As long as there is no acknowledgment, a clearance cannot be considered as having been issued...
Then the controller has to manually feed the system with the clearance that has been issued...
Add up all this time and you come out with scores of seconds possibly approaching a minute or more.
Measured in terms of communication speed, digital link wins hands down in all but the simplest traffic situations.
With the system capabilities more than proven and being aware of the difference between message transit times and communication speed, we can safely forget about the mantra of non-time critical messages only.
Except for the rare emergency intervention, digital link should be the norm in the future.
And the future? VDL Mode 2/ATN has a lot of mileage in it and will serve aviation well for many years to come.
The EU mandate on digital link equipage ensures that both the ground and the airborne elements of the system get in place in an orderly manner.
Curiously, the mandate does not talk about any commitment to actually use the equipment.
Obviously, this was a step too far even if we all know that additional capacity enabled by air/ground digital link can only be declared if its use is not dependent on local decisions...
Work is progressing in leaps and bounds on defining the future aviation air/ground digital link that will satisfy all the communications needs between aircraft and the ground, be it voice, text messages, digital maps or whatever.
In Europe we will be looking at SESAR to deliver this new bit of technology and its applications.
What was left out? This is not a comprehensive history and I am sure others would have put the accent on other events or the focus on other hidden "gems".
There were and still are many experts and organizations who have done a lot for the advancement of digital link whom I could have mentioned but because of the need to keep this piece relatively compact, I chose not to.
But the vital roles played by organizations, companies including airlines, must be recognized.
May be they will get their own story in the not too distant future.
Because of the slow down of traffic growth in the wake of 9/11, the expected ACARS problems did not materialize and the ATC frequency congestion was also pushed far into the future.
In other industries, such a period of respite might have been used to prepare for the times when business recovery would once again make air//ground digital link essential.
But that is not how aviation works.
With the immediate threat receding and even some of the big carriers fighting for survival, enthusiasm for investing in things that would generate benefits only many years down the road cooled.
Of course for the planners of the ATM system this was a situation that spelled trouble for later.
The frequency congestion problems were not a mirage even if for the time being those problems slipped into the future.
The need to put together a comprehensive kit of capacity enablers had not become less important, only the urgency had changed somewhat.
For LINK2000+ the big question was: how to jump start equipage? The question was not self serving at all.
If Maastricht UAC controllers did not get digital link equipped aircraft to work with, it would be impossible to build and maintain proficiency and to shake down the system in real operational circumstances.
The solution was simple...
money.
A proposal was put forward to EUROCONTROL that called for a set of pioneer airlines who would get (part of) their initial investment paid and they would then form the core of equipped aircraft in the hope that after a time others would also follow as the potential benefits came near in the bean counter calendars.
The "pioneer" idea was a big success and LINK2000+ managed to line up an impressive number of airlines and aircraft.
What was never said openly was of course the fact that the pioneer airline success was also a clear demonstration of how effective a bit of infrastructure help can be in solving air traffic management problems.
Politicians shooting from the hip take note...
Finally all on board Of course in time also Airbus came on board as did the other airframe manufacturers before them.
Air/ground digital link became recognized as one of the premier capacity enablers in both SESAR and NextGen and air navigation service providers across Europe are working on their implementation programs.
The question is now not if, but when.
It is easy to make the mistake and think of air/ground digital link as something we need only in congested airspace.
After all, where there is no congestion the frequencies will not be congested either, so why spend money on digital link? There is some truth in this but on the other hand, if a pilot has to fly across the continent and keep switching between voice and text messages, the situation might very well become untenable from a safety point of view.
Operational uniformity has its advantages and the biggest investment is on the aircraft so why not use it everywhere? This idea of universal digital kink usage is sometimes countered by the airspace users saying that voice is free while digital link usage carries a price tag...
Well, voice is not free.
Has never been.
Is the use of the ILS or the VOR free? Of course not! The costs of voice are simply "hidden" in the charges in general while the cost of digital link usage is (in part) payable by the airspace users.
The important aim must be to ensure that there is no double charging...
Who uses digital link should pay for that and that alone...
Digital link...
for non-time critical messages only? In the early days of digital link usage, the greatest worry was the time it would take for messages to get from the controller to the aircraft and vice versa.
This worry was fuelled in no small measure by the perception by controllers that voice is faster than digital link.
What was often forgotten was the parallel versus sequential nature of digital link and voice, respectively.
A lot was made of message transit times and very little talked about actual communications speed.
Very rare, extreme cases apart, the digital link message transit times end to end are measured in a few seconds or, more commonly, in fractions of a second.
Compared to the "instantaneous" contact voice seems to make possible, this is indeed a "long" time.
Voice does not have a message transit time on the VHF AM radio...
But if we look at the communications speed in a congested voice environment, we get a very different picture.
The moment the controllers decides that he or she has a message to send, the frequency may not be free...
so they wait.
Then they start talking but the receiving aircraft may or may not be able to acknowledge right away because of the same frequency congestion problem.
As long as there is no acknowledgment, a clearance cannot be considered as having been issued...
Then the controller has to manually feed the system with the clearance that has been issued...
Add up all this time and you come out with scores of seconds possibly approaching a minute or more.
Measured in terms of communication speed, digital link wins hands down in all but the simplest traffic situations.
With the system capabilities more than proven and being aware of the difference between message transit times and communication speed, we can safely forget about the mantra of non-time critical messages only.
Except for the rare emergency intervention, digital link should be the norm in the future.
And the future? VDL Mode 2/ATN has a lot of mileage in it and will serve aviation well for many years to come.
The EU mandate on digital link equipage ensures that both the ground and the airborne elements of the system get in place in an orderly manner.
Curiously, the mandate does not talk about any commitment to actually use the equipment.
Obviously, this was a step too far even if we all know that additional capacity enabled by air/ground digital link can only be declared if its use is not dependent on local decisions...
Work is progressing in leaps and bounds on defining the future aviation air/ground digital link that will satisfy all the communications needs between aircraft and the ground, be it voice, text messages, digital maps or whatever.
In Europe we will be looking at SESAR to deliver this new bit of technology and its applications.
What was left out? This is not a comprehensive history and I am sure others would have put the accent on other events or the focus on other hidden "gems".
There were and still are many experts and organizations who have done a lot for the advancement of digital link whom I could have mentioned but because of the need to keep this piece relatively compact, I chose not to.
But the vital roles played by organizations, companies including airlines, must be recognized.
May be they will get their own story in the not too distant future.
