Originally Posted by
Roffa
Also, to the best of my knowledge, a Mode S transponder is a Mode S transponder. ELS and EHS are basically just terms that someone has made up to indicate whether or not anything extra by way of DAPs is being downlinked back to the ground from a suitable source in the aircraft via the Mode S datalink.
I look forward to future discussions* about why GA is having to buy yet more boxes because the ATC system is shifting towards ADS-B or some other type of 'progress'. You just can win, can you
* Actually I don't because I'm reasonably confident I'll be retired by then!
EHS transponders may be identical electrically (I don't know), but they are more expensive, require antenna diversity, much more certification and a whole lot of onboard data capture (effectively a certified FMS costing more than GA aircraft).
The CAA make the RF argument, however, the US, with higher total traffic density in mandatory mode-C areas and much more extensive deployment of active tas (in non-mandatory aircraft) doesn't seem to have the problem - maybe radar just works better over there
The essence of my point is a lot of money has been spent by light GA for something which adds no value and contributes no value to CAT (obviously one hopes CAT and NATs received significant value from the CAT investment and NATs radar upgrades).
ADS-B on the other hand should enable many many people to have much more traffic information onboard and for the ATC services to shed substantial costs and/or improve service. The US is likely to be ADS-B for all before Europe has co-ordinate rolling the Mode-S value beyond the early adopter country/areas. So another 'Mode-S mandatory' irritation was the blind implementation of a plan 15 years behind schedule, when the technology was already becoming obsolete.
Sadly, the way Europe as historically worked, you can see US ASD-B providing excellent traffic, weather, TFR, etc data to GA and European ADS-B providing the minimum possible value to GA while passing the value of the investment exclusively to the shareholders of NATS and operational improvements to CAT (because GA doesn't 'pay').