Mode S

[flybymike]

Currently downlinked via Mode S from suitably equipped aircraft are selected flight level, indicated airspeed, heading, groundspeed, rate of climb, rate of descent and flight id. Coming soon is set barometric pressure setting.

If I may play the cynical devil's advocate here, perhaps I am being naive but could it not be said that:

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.

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.

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.

4.Groundspeed must already be computable from existing systems.

5.Rate of climb and descent must already be computable from rate of change of altitude given by existing transponders.

6.Flight ID is useful for policing but not relevant to traffic control.

7.Barometric pressure setting is again a matter for crew and not ATC checking and policing.

[Roffa]

mm_flynn,

I was initially responding to chevvron's rather sweeping...

'What's the latest on Mode S'?
It's an unnecessary waste of money as only a very few ATC units can make use of the extra information.(LARS units the ones who need it most - generally don't have the necessary software)

Then tried to answer your question during which I did say you may consider Mode S may not be entirely relevant to you.

That said, I think it should be stressed that even if not directly relevant to you it does make for an overall safer system. That may or may not in itself be of a measurable value to you or anyone else here.

I suppose there's also the spectre of mandatory transponders still on a distant horizon. I'm no technical expert on the subject but I believe if we ever get to a position where pretty much everything is carrying a transponder then the bulk of them will have to be Mode S for radar processor info overload reasons (though I stand to be corrected if that's not the case).

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!

[Roffa]

flybymike,

Your post possibly is cynical devil's advocate, possibly naive, certainly lacking in understanding.

[flybymike]

flybymike,

Your post possibly is cynical devil's advocate, possibly naive, certainly lacking in understanding.

Fair enough. I am a simple bear and I was just asking.
Please educate me.

[mm_flynn]

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').

[BackPacker]

Please educate me.

I'm not the expert, but it seems to me that all the data that's being transmitted by an "enhanced surveillance" mode S can be put into a computer straight away, and the computer will then calculate where the aircraft is going to be in a few minutes time, where everybody else is going to be in a few minutes time, and whether that's going to lead to any conflict.

That's an essential condition for "free flight" which essentially means that IFR flights can fly DCT from departure to destination instead of having to fly fixed routes. And that, in turn, may lead to significant savings in fuel and time. Plus it will allow more efficient use of airspace and better timings of arrivals so runway use can be optimized.

Of course you can derive some of the data by observing the radar track for a few minutes but that will be slower and doesn't take into account things like speed/heading/altitude changes. If you know what the FMS has been set to (including current and set airspeed, current and set heading, rate of turn, current and set altitude/fl, rate of climb or descent and current wind conditions) it's far easier to predict what the aircraft is going to do in a few minutes time. And that's essentially what EHS is about - uploading the most important FMS parameters to the radar controller.

I agree that a human cannot possibly comprehend all data that's being transmitted by 100s of mode-s transponders simultaneously. But a computer can.

[chevvron]

I was trying to ignore Roffa's comments on the grounds he seems to have little perception of what it is like for a private pilot to instal this equipment, and the fact this forum is entitled PRIVATE (not commercial) flying. Sure I recognise the benefits for controlling IFR traffic in controlled airspace, but unless NATS reduces its charges to 'pipe' SSR information to smaller ATC units, especially those providing LARS, it will have absolutely no benefit for those ATC units and hence the users - PRIVATE pilots - will have spent all that money for no benefit to themselves either.

[Roffa]

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.

[flybymike]

Many thanks Roffa. The bear is indeed more educated and did indeed find it of interest. The bear has a few reservations on some of your points but would not generally take too much issue with them.

Personally I cant wait for ADSB and pilot interpreted control, but I think I will be six foot under before it arrives.

[mm_flynn]

Roffa,

Thank you for a clear picture of what data elements are useful and why. It corresponds well to what I had expected (other than the IAS for approaches, which I had forgotten about).

I was slightly surprised you didn't mention the vertical view of the stack, which I am lead to believe requires mode-S to be robust.

Equally, your list does confirm the predominate advantages for mode-s relate to the enhanced version which is not what GA is able or been required to fit. As such, my mode-s spend benefits no one. As Chevvron said, if all of the data that is now being collected at GA's expense where being shared out at marginal cost to people/agencies to make use of it, I suspect there would be a much more positive view of the deal.

M

[Roffa]

mm_flynn,

I thought I'd mentioned the VSL before which is why I missed it out (didn't want to upset chevvron any more than necessary!) The VSL does require Mode S.



I really will now bow out.

[IO540]

I don't recall anybody ever showing that Elementary Mode S having any value whatsoever to ATC, or to anybody else, over Mode C.

Hilariously, if you get the installation manual for say the GTX330 you won't find any reference to "elementary" or "enhanced". This is because these terms are a purely European invention, done without looking at equipment actually on the market.

A GTX330 will radiate all data connected up to its RS232 or ARINC inputs.

The better equipped GA could thus radiate additional parameters (certainly GPS position, track, GS, etc) but they are not allowed to because the radiated parameters have to be documented in the POH supplement and such a doc change is an EASA Major Mod, costing 4 digits

So ATC are never going to get the extra stuff which they claim is what makes Mode S useful.

Only some planes, imported with Mode S installed and left on their original registry, emit the extra data.

The image posted by Roffa has been shown by NATS for several years now. I saw it on a visit to West Drayton. NATS have been trying to sell this software to other ATC units and they are very proud of it. But it has zero relevance to GA because GA will never be allowed to emit the data even if it had it.

The other thing is that, from some enquiries made, it appears that the NATS software suppresses the extra data anyway, for "GA" targets. One pilot whose GTX330 definitely emits the GS (because his GTX330 is - like many - set up to use GS to switch between AIR and GND modes) has asked Mode S equipped ATC if they can see it, and they cannot.

It has been a total farce. I recall UK's best known avionics shop publishing a press release a while ago, saying they have to effectively cripple hundreds of Mode S installations, because EASA threatened that radiating the GS parameter is illegal. Later, Garmin promised to modify the GTX330 firmware to include a config option to not radiate this stuff; this is I think in place now but only long after most IFR pilots installed the unit. I have such an installation myself but "fortunately" the GTX330 fails to accept the GS parameter from the KLN94 in the first place so, gosh, I got away with it and I am 100% legal

Roffa may not like this but like I say there is really no, zero, zilch, absolutely nowt, benefit to ATC through GA having Mode S.

[mikehallam]

Dbtlss u all undrstd t abv thread's many abrvvns ? I no a phew !

e.g. CAA Mode-S IFR VFR ATC LARS Mode C TMZ
ADSB using ES NATS EASA TBM850s EHS CAT SFL IAS ROC or ROD ROC/ROD GA VSL
A GTX330 will radiate all data connected up to its RS232 or ARINC inputs. GTX330 definitely emits the GS (because his GTX330 is - like many - set up to use GS to switch between AIR and GND modes) has asked Mode S equipped ATC.

Meantime Farnborough RADAR radio in the south east persists in giving a patchy 'service' (I know it's free).
BTW I could instead be happily & foolishly thinking of listening out with a (very) BASIC service on Shoreham, or Goodwood, or instead using SafetyCom, or not bother at all !

That's five categories of communications a lone flyer in free airspace could be into. Surely this simple system could be organised and functioning cohesively for separation, using current bog standard gear, before making all the fuss about expensive esoteric electronic wizardry, with which magic men in "ATC" will somehow ensure the air in front of one is empty !

[chevvron]

Roffa: Having spent the last 24 years involved in light aircraft ownership, had a PPL for 39 years and spent 41 years in Air Traffic Services, the last 36 of these 'rubbing shoulders' with the light aircraft and private/recreational flying community, I accept that you are obviously far more knowledgable than I on the subject of Mode S, but I can't help being sympathetic with the viewpoint of current owners.
From an ATC point of view, it's nice to have (but is it really necessary?), from an aircraft ownership viewpoint it's an expense which in my opinion is not necessary when you only intend to operate a permit aircraft in VFR outside controlled airspace. Rather like radar/radio on a privately owned boat, if you're going out to sea then by all means have it; if you only intend to cruise canals or inland rivers, why bother?

[HEATHROW DIRECTOR]

I keep reading "checking and policing" by ATC. Presumably written by somebody with absolutely no experience of ATC or flying?

[Rod1]

I take the point on abbreviations;

ES = extended squitter

ADS-B = Automatic Dependent Surveillance Broadcast

When the CAA decided not to implement the original idea that everything that flew had to have mode s, it embarked on a three-point plan. Phase 2 will complete in March 2012. Phase three, which did not have a fixed timeframe, was the addition of ADS-B (Automatic Dependent Surveillance Broadcast ) using the ES (extended squitter) feature of mode s transponders. This allows for the transmission of additional data, including position, heading and speed.

In order for the Mode s transponder to transmit this data it needs to get it. The source is a GPS. Just about any aviation GPS can do this, but I imagine it will not be as simple as that in Europe.

When the avionic shops were advertising the Mode S was coming fit it quick, Garmin were rubbing their hands together with glee. Unfortunately a number of companies launched fully approved units at significantly lower cost. In response Garmin launched a low cost unit called the 328. This unit is the only mode S unit I know of which does not support ES so cannot be used for ADS-B. The avionic shops pushed this unit for all they were worth. The CAA warned against fitting it at various consultation meetings. The unit is the most popular Mode S unit in the UK by some way. When ADS-B comes in there are going to be some very unhappy pilots, and some very happy avionic shops.

In a sensible world the CAA would have encouraged people to enable ADS-B on installation of an appropriate transponder (assuming a suitable GPS was available). Far from it! To enable it they decide it was a major mod costing £1000’s.

Hope that helps!

Rod1

[flybymike]

I keep reading "checking and policing" by ATC. Presumably written by somebody with absolutely no experience of ATC or flying?

I already said, I am just a stoopid bear. I have no experience of anything except having innocent questions belittled with snide remarks from the Glitterati of the forum. No wonder there are threads about people baling out of here...

[Jan Olieslagers]

Hilariously, if you get the installation manual for say the GTX330 you won't find any reference to "elementary" or "enhanced". This is because these terms are a purely European invention, done without looking at equipment actually on the market.
A GTX330 will radiate all data connected up to its RS232 or ARINC inputs.

This intrigued me enough to trigger some original research. I found the GTX330 to have 2 RS232 inputs, one seems meant to read an altitude encoder, the other might be used for GPS input; and 4 ARINC_429 inputs. It can also read altitude information in the "old style" gray-parallel encoding.
These inputs are not automatically read, they need to be configured; i.e. one must indicate what info is offered on which input.
True enough the manual does not say anything about "elementary" or "enhanced". But is does mention a "diversity" mode, only available in the TX330D model, which requires installing a second antenna on top of the plane - the main one being on the bottom. What is this "diversity" mode? Something USA-specific, perhaps?

[IO540]

The diversity mode, AFAIK, is to support two aerials to improve visibility to other aircraft flying above/below you. The enhanced Mode S installation in e.g. a TBM850 uses this.

You are right that the inputs can be disabled but if e.g. you bring in the GPS GS to get automatic AIR/GND switching, you have to enable that input to make that function work, and the GS is then radiated. The only "legal" way in the EU is to use a landing gear squat switch, or an airspeed pressure switch, to drive the GTX330, but these involve a lot more work than using the GPS GS, both actual and paperwork.

I am not up to date on this (all IFR pilots I know installed the GTX330 years ago) but Garmin were going to change the firmware to enable the GPS GS to be thus used but without being radiated.

In a typical GTX330 installation done outside Europe, you connect everything you have (the whole NMEA data stream, etc) to the GTX330, enable all the inputs, and it all gets radiated. In the USA, the more the merrier