flybymike,
Fair enough. I am a simple bear and I was just asking.
Please educate me.
Okay...
1. Selected flight level is the job of the crew and not a matter for "checking" by ATC. Actual flight level is of course already available from Mode C.
For 99% of the flight SFL = cleared level. ATC are required to check cleared level when giving a clearance. SFL downlinked allows additional checking of cleared level in addition to the aural one on the r/t. In the not too distant future, with electronic flight data in use on the ground, this additional checking can also be done automatically in the background. There are other uses as well. It also allows the use of tools to indicate when two aircraft in close proximity have the same selected level, for example in a holding area. Two aircraft in a hold having the same SFL, i.e. cleared level, is not generally a good thing.
2. Indicated airspeed cannot be relevant to ATC apart from again "checking and policing" purposes. Ground speed is what they are interested in for planning purposes and presumably is already computable from existing radar rate of change of position information.
IAS possibly primarily of interest in the intermediate and final approach areas when very tight separation tolerances are used. Allows ATC to ensure accurate speeds are being flown during periods of minimum in trail separation and also background automatic monitoring warning/guarding against 'catch up' incidents.
3. I don't understand what advantage heading info would be over track info other then to save a few micro seconds during vectoring. Track info is already available from conventional radar.
Having heading info can save on r/t on congested frequencies. Perhaps not vitally important but useful nonetheless.
4.Groundspeed must already be computable from existing systems.
Radar derived groundspeed is not particularly accurate compared to getting the info down from the aircraft. Groundspeed is useful to know.
5.Rate of climb and descent must already be computable from rate of change of altitude given by existing transponders.
You can watch the rate of change in Mode C in a sweep and multiply that by the rpm of the radar to get ROC or ROD. I suppose we could stick with the simple arithmetical option instead of using the downlink, but over the years the educational requirements for controllers have been reduced and we're not as smart as we used to be. ROC/ROD can also be used in conflict prediction tools (along with some of the other DAPs).
6.Flight ID is useful for policing but not relevant to traffic control.
Flight id should, hopefully, eventually do away with the need for individual Mode A squawks and will also be integrated into the ATC flight data processing system i.e. on the radar I will see the downlinked flight id on the radar label data block rather than callsign derived from a four digit squawk which is then paired on the ground with a flight plan held in the processing system or just the squawk on its own.
7.Barometric pressure setting is again a matter for crew and not ATC checking and policing.
Whenever a pressure setting is given by ATC it is a requirement to ensure it is read back correctly. Even when this is done the occasional incorrect readback is missed or, it is read back correctly but set incorrectly. An incorrect pressure setting may at best lead to a level bust with a potential for a loss of separation. At worst, especially when operating close to the ground, it may kill. The downlinking of the set barometric pressure in the aircraft will allow automatic background checking that the correct pressure setting is being used in the cockpit for the stage of flight.
I hope that the bear is now a little more educated and may even have found the above of interest.
Chevvron, I apologise for trying to add a little value to the 'PRIVATE (not commercial)' forum by posting the above. Even if not of total relevance to everyone here I do hope some background info may be of interest. In finishing I suppose only having had so far around 10 years or so of involvement with light aircraft ownership, plus a bit more in ATC, my perception is not up to your own so I will now acknowledge your patronage here (though still disagreeing with some of what you write), apologise again for my intrusion and bow out gracefully.