Though there are few who will not be familiar with the term Mode S Enhanced Surveillance, let me quickly recap. Mode S is a legacy, ground based surveillance system which has a rudimentary data link capability. It is this latter that was being pushed in the 90s as a solution to all ills of air traffic management. Using the link capability, certain parameters from the aircraft, the so called DAPs, can be sent to the ground ATM system. Part of these are for display to the controller and part serve in theory to enhance system functions.
Back then the airspace users saw clearly that the benefit claims made for Mode S EHS were grossly overstated. It did not help that the first business case created for Mode S EHS was, to put it mildly, questionable. A later version showed more realistic figures but the damage was done.
A bitter fight ensued between the airspace user community and the air navigation service providers, with EUROCONTROL caught neatly and uncomfortably between the two. Not that all States saw things in such rosy colors. Many of them felt that the investment being asked from the airspace users was unjustified in view of the benefits expected.
The proponents themselves had diverging agendas but none could actually show a solid case that would justify the investment on the industry level.
Other than the lack of benefits, it was this lack of clear commitment from the ground that was at the basis of the airspace users’ opposition.
In the end, Germany, the UK and France decided to jump ship and publish a Mode S EHS mandate on their own, regardless of what the rest of
Europe (or the world for that matter) would do. This was the famous Three States commitment (in 2000 if I recall it correctly) which promised to have everything ready to go on the ground by 2003.
As time passed, several other modifications to the Mode S transponder came on the agenda and the airspace users were now fighting to have the rule makers combine things to put some sense into the rather confused landscape.
It is educational to now cast a wary eye on the site of the MSA (Mode S and ACAS program) web page and read the latest information on the status of Mode S in Europe (updated October 2009). The UK has “successfully” implemented EHS in the London TMA in December 2005, the Manchester TMA in Q1 2008 and the ACCs will follow in 2010.
Maastricht UAC has EHS since July 2009 but with only two parameters being available, with more to come… eventually.
France….? No information yet, except that 2009 should see “success” there also…
Benefits? No information… What does it mean that they successfully implemented Mode S EHS? Having a bit more information available on the ground is no success. Surely they were sure the thing would work before spending all that money on something so fiercely opposed by the industry.
We are reassured though that several other States have indicated their intention to introduced EHS in the near future. For what exactly? What are their expectations?
Mind you, Enhanced Surveillance’s little brother, Elementary Surveillance is not the issue here. ELS was needed to solve the SSR code shortage (even if it is debatable whether this was the most cost effective way of going about it). But EHS is a much bigger step and much more expensive…
That Mode S Extended Squitter has ushered in ADS-B is also not in question.
The question has always been and continues to be: what benefits is Mode S EHS bringing to anyone anywhere? In quantified, actual savings, efficiency increases, safety, whatever… not in theory but at the places where it has been “successfully” implemented.
The airlines had a real problem meeting the mandate, some even parked aircraft to enable them to catch up. The money had been spent and the aircraft have been flying for years with the equipment without generating any benefit at all. Or was there a benefit we just do not talk about it in the status reports?
The problem with the Mode S EHS saga is not only that it saw the reasoned user position overruled by parochial interests which then failed to deliver in time (and substance we may add) but that it also discredited the process of introducing new technology, a situation from which it is very difficult to recover. Almost as difficult as showing real benefits for Mode S EHS.