Mode A code shortages

[bookworm]

According to a 2001 Eurocontrol study, the effects of Mode A code shortage, which is the cornerstone of the case for Mode S equipage, should be kicking in and causing delays round about now, particularly in the London FIR. So, two sets of questions:

1) Is it currently possible to avoid allocating a Mode A code to an aircraft with a Mode S transponder? Is this the current practice? If not, when will we reach the point at which equipage with a Mode S transponder will "save" a Mode A code.

2) What evidence is there that we are at or approaching the capacity of Mode A codes in the London FIR (or elsewhere)? Are flights currently delayed through shortage of codes to allocate? If not, is there a way of finding out how close to capacity we are?

Thanks

[BDiONU]

In the UK mode 'S' is only under trial at specified locations. So it is not possible not to allocate a mode A.

Although there are currently no delays in UK it is only because codes are re-used quite quickly. This does occasionally trip the NAS computer up and aircraft are occassionally issued the same code, although not for long usually. Something that is being worked on. I would not like to speculate as to how close to capacity we are but given the general downturn in traffic not ver very, just quite :)

[FWA NATCA]

Bookworm,

In the US we run out of transponder codes almost weekly so we see proposed flight plans being assigned generic codes of 3100, 5400, etc. Since most approach controls have code subsets assigned to their facilities we can assign one of our local codes to any flight plan that has a generic code.

As for Mode S some facilities have the Mode S antennas and most don't.

Mike

[RaRadar]

The way it is intended to work (at least in Europe) is that the Mode S ground station extracts the Aircraft Id (Flight Id) directly via the Mode S datalink. This means that there is no need for a Mode A code/callsign look-up at the centre for Mode S equipped aircraft which will all have the same Mode A code. This frees up Mode A codes for non-Mode S targets.
Before this can happen we need operational Mode S radars, aircraft that support this feature, changes at the centre ….
I hope we can struggle on for a bit longer.

[BDiONU]

Have taken some 'expert' advice on this now.

Mode 'S' will not appear anytime soon in UK. Although its essentially a software upgrade for the ATC radars the main UK radars require to be replaced (not only for mode 'S'). NATS had a 10 year plan to replace them all, but the cost is now £150million and with the HUGE debt NATS has the interest repayments have crippled that size of investment.

In UK during the summer usage of mode 'A' squawks reaches 95%.

[bookworm]

Thanks for the info, all.

BDiONU

3) Is the proprotion of Mode A codes in use published somewhere?

4) You seem to be suggesting that the upgrades to ground equipment to take advantage of Mode S will be delayed against an original plan. Are there details published of a) the original plan and b) the revised schedule, or are you deducing the inevitability of delay from NATS's dire financial situation?

Mike

5) What is the FAA policy on aircraft equipage with Mode S? Is it required on aircraft over a certain size, or Part 121/135 or something else? What's the plan for the future?

6) What are the consequences of the code shortage? Does it delay flights? Do you limit capacity to cope with the extra workload of having to use these local codes? What's the "cost" of the problem?

BTW I can answer part of my question 1 from published Eurocontrol Mode S stuff. When Mode S is fully implemented, a conspicuity (non-unique) Mode A code will be allocated to aircraft. But I would appreciate any guidance as to how far down the road to Mode S we have to go before discrete Mode A codes start being preserved by that process.

[BDiONU]

3) Not to the best of my knowledge. I would say its buried in one of NATS (in confidence) papers somewhere. I have access to several NAS experts and asked them.

4) The original plan was in the long term NATS strategic business plan and was due to be complete in 10 years time. This plan is now on hold. No deduction on my part. No, these details are not published in the public domain. If you're a NATS employee mail me and I will point you to the plan on the intranet, its not a secret.

Sorry if I seem to be only telling 'bits' but obviously company confidentiality forbids indiscretion.

Part answer to 6) for UK is that because NAS FLAT tracks aircraft the UK does have the ability to use specific codes for more than one aircraft. So it is quite possible to have several aircraft on the same (preferably one of the sector discreet codes) code, but with the TDB displaying the correct callsign etc. But we do not do that.

[bookworm]

Sorry if I seem to be only telling 'bits' but obviously company confidentiality forbids indiscretion.

Absolutely right. To clarify, I'm not a NATS employee and I'm only looking for information that's in the public domain.

I'm trying to work out how to respond to the CAA's Regulatory Impact Assessment that would have aircraft operators spending hundreds of millions of pounds on Mode S related avionics. The cost benefit analysis, dating from 1998, hangs on overcoming two major issues, Mode A code shortages and RF congestion in the 1090 MHz region. The claimed benefit appears to be very sensitive to how close the current system is to saturation, and I'm trying to put together a picture of how accurate 1998 CBA will be.

Part answer to 6) for UK is that because NAS FLAT tracks aircraft the UK does have the ability to use specific codes for more than one aircraft. So it is quite possible to have several aircraft on the same (preferably one of the sector discreet codes) code, but with the TDB displaying the correct callsign etc. But we do not do that.

This intrigues me. What is "NAS FLAT"? Are you saying that in the current system, the same Mode A code could be used for more than one aircraft in different parts of the UK, but the feature is not used?

[BDiONU]

O I C. Before 9/11 traffic levels were rising year on year at about 6%, so saturation point would have been very much more quickly reached than at current traffic levels (although they are rising on internal flights with the boom in low cost carriers). I should think that the CBA in '98 was based on the pre 9/11 traffic levels and predictions.

RF congestion has been addressed to some extent by the introduction of 8.33 frequency spacing.

NAS is the UK's Flight Data Processing computer system and is absolutely integral to ATC in the UK. It processes the flight plans it gets from Brussels and distributes the flight data to all the relevant ATC sectors. It allocates the mode 3A code. It sends beacon estimates to units external to the NAS system and internally to NAS equipped units.
The reason it can send estimates is because it is linked into the UK radar system and tracks flights using their SSR code. NAS will 'watch' for an aircraft to get airborne and when it 'see's' the squawk it pairs it to the flight plan which NAS allocated the squawk to. It then tracks the flight and 'knows' its route, hence Flight plan Aided Tracking (FLAT). In addition to using radar NAS has a simple 'idea' of particular aircrafts speed, climb rate, rate of turn etc. plus it uses forecast upper winds to give estimates for beacons along the flights route. As an aside it is this 'idea' which we are very keen to have modernised to vastly improve our trajectory prediction (TP). More upper winds put into the airspace model, more realistic aircraft performances based on length of flight etc. The more accurately we can predict an aircraft's flight profile the more accurately we can predict where it'll be in the future and hence a big step forward to medium term conflict alert instead of our current short term version.
Not unusual for NAS to pair a track to a flight if, say the pilot has input the wrong squawk. Once the aircraft squawks the correct squawk its necessary to 'break' the pairing to allow NAS to correctly pair it up again. I have to admit I did not understand the technical reasons why it is possible to have more than one aircraft on the same squawk and still have the correct callsign etc. showing on the radar. Our 'professor' talks a much higher language than us mere mortals ;) but he assures me it is feasible.
However I think I may have lead you slightly up the garden path because I'm talking about UK and I suspect the real problem lies within the ORCAM region, but I don't know.

Sorry to burble on at length but couldn't think of a way to precis things. And if anyone can provide a better explanation of NAS than my rather off the cuff one please feel free to correct me :)

[bookworm]

Thanks for the detail BDiONU

RF congestion has been addressed to some extent by the introduction of 8.33 frequency spacing.

Just as a point of clarification, the supposed benefit is relief of congestion of the radio spectrum around 1090 MHz where the transponders work, not of the aeronautical comms RT frequencies. I thought exactly as you did when I read the "RF congestion" section title in the CBA, but what they're getting at is basically that the selective nature of Mode S means that there's less going on at that frequency.

[Minesapint]

Samll point. Our (UK) NAS will not initiate a track on codes ending 00.:)

[BEXIL160]

Hmm.... My old mate Take3 etc is more or less right, but i seem to recall that CCDS (Code/callsign distrubution system) allocates (and pairs) codes issued in the London FIR.

Hence when NAS is unavailable (shutdowns/ FLOPS) CCDS is still there so you can manually pair up code / callsign / dest / exit point.

I think?

Rgds BEX

[BDiONU]

Yes your right Bex, CCDS is the beast wot does it. Just trying to simplify fings!! :)

[Hippy]

This is all v interesting, even if it has wandered slightly off track. Now I've got a question for the techy types:
The consoles in the MASOR use the CCDS for code/callsign pairing, but there is also something that provides beacon estimates as well. Is it the same system (NAS) as used by the civil sectors, or is there a seperate system that provides estimates in the MASOR?

TIA
Hippy.

[BDiONU]

EDDUS. Which is plugged into NAS.

[Minesapint]

NAS (or humans) allocate codes then tells CCDS. Not the other wasy around.:)

[BEXIL160]

Aha..... There you go. Yes that would make sense wouldn't it? I knew CCDS came into it Somewhere.

I have a dim and distant memory of code allocation pads in use on the assistant positions at ScATTC, and lots of phone calls down south with each estimate.:)

Even more "slight" thread creep (sorry). Just when will NAS be replaced? The Americans are in the process right now. How far have "we" got?

Anyone know for real?

Rgds BEX

[bluskis]

I confess to being a little lost in the large amount of detail in the replies to Bookworms question.

From the light aviation standpoint, where most airplanes do not have an FMS, so cannot give the added information, and are probably only on flight planned routes for a small percentage of their flying, the main advantage of equipping light airplanes with Mode S appears to be in avoiding TCAS uncertanties.

Bookworm, when you have absorbed all the information, could you post your conclusions as you seem to have a greater understanding of the salient points than do I. Thanks.

[bookworm]

Happy to do that bluskis.

I'm actually thinking of the cost-benefit issues for a Mode S Elementary setup - in other words you pull out your Mode A/C transponder and stick in a Mode S one, connected to nothing more than an encoding altimeter. No FMS required. That's what's proposed for aircraft < 5700 kg in the TMA for 2005.

The purported advantages of this rest on two issues, both related to capacity.

1) There are a limited number of Mode A codes available
2) There's congestion at SSR RF frequencies when Mode A/C is used.

I'd like to understand whether these are real issues, now, and if not, when are they likely to be serious limits to capacity.

[Minesapint]

For the computery and mathematically uncallenged the current mode A code numbers are octal - 0 to 7. You will never see an 8 in an ssr code. Digital, even 4 digits, can go to 9999, lots more but not enough. Individual 'ident' is the answer but a few years away yet I fear.

:)

[bluskis]

Minesapint

There should be 6143 individual codes available accounting for 3 lost to emergency use.

Perhaps a rethink on how to use these would have been in order, with the option of having a smarter ground based system for handover purposes etc.

However it is obvious things have moved a lot further down the skyways.

It is still difficult to see how 6134 numbers can be used up in the relatively localised coverage radar provides.

I can see how bandwith can be saturated, but by interrogating at intervals, which may well be how it is done a present, should have alleviated the problem.

Is it the same committee designed approach that has resulted in a population of 60 million including babies requiring some 10 billion telephone numbers to cope?

[Minesapint]

I think that the commitee approach is a part of the problem. People from all over Europe meet to divide up the available codes.

When you take into account civil domestic, transit, super domestic, sector codes, orcam etc its very easy to see where they all go.

Our radar can often see foreign military codes over France and Holland causing numerous problems. In the octal system with 4 digits you get 4096 codes. 7000 / 77/76/7500 are obviously reserved but so are many others...... each ATSU has its own block of codes allocated to it. Often these units are closed at evenings and weekends. Why not use these codes when they are as a short term measure? Complicated but could be done.

[Scott Voigt]

BEX;

I wouldn't hold my breath for our remake of NAS. We are indeed working on it, but the final contract hasn't been signed yet, and I have no doubt that the FAA could muck it up if they really put their mind to it. There are a couple of folks at the puzzle palace who may or may not want to wait the time required to do it right. We will hope and wait and see.

regards

[FWA NATCA]

Bookworm,

>5) What is the FAA policy on aircraft equipage with Mode S? Is it required on aircraft over a certain size, or Part 121/135 or something else? What's the plan for the future?

You might ask Scott Voigt ( [email protected] he also participates in the ATC conference) this question as he is more knowledgeable than I am on Mode S and the FAR's.

>6) What are the consequences of the code shortage? Does it delay flights? Do you limit capacity to cope with the extra workload of having to use these local codes? What's the "cost" of the problem?

Running out of transponder codes, is an indication that we are probably busier than one arm paper hangers, and that there are probably delays being encountered within the system, these delays could be a result of weather, equipment failures, or heavy traffic.

When we run out of transponder codes we usually see messages from the Flow Control desk asking that facilities not enter VFR flight plans into the NAS.

As for extra workload of entering local codes it takes a controller less than a minute to enter a local code via the FIDO. Again Scott works at a much busier facility than I do so he may be able to share how this problem affects our larger facilities.

Mike
NATCA Local FWA

[Scott Voigt]

Actually, the e-mail is [email protected] <G>... But with that.....

Mode S is only required due to TCAS. If you are a commercial aircraft with 30 ore more pax ( I believe that is still the limit) then you must have TCAS on board. The more pax that you have the more advanced the TCAS system.

If you have a TCAS on board for your own feeling of bliss, but aren't required by regulation to have it, you will still have a mode S transponder so that it can talk to other TCAS units.

As to running out of codes. It happens from time to time, however, we don't really ever run out of codes for active aircraft. What we run out of codes for are those who are waiting to come into our airspace or those on the ground who haven't recieved clearances yet. What the causes, is the controller will not be able to allow an aircraft to use the same code that he / she was using when they were in the last facility due to someone already using it in your facility. You then assign another code. The problems that you will run into on the ground is that you may not have codes available to you until just a few minutes prior to departure, vrs. 30 min. to an hour.

regards

[West Coast]

TCAS I required for 10 to 30 seats, TCAS II required for more than 30 seats.

[asdfgh]

Despite some thoughts on here that CASPIAN (Commercially Available System Promoting Integration Across NATS or Commit All SDI People Into A Nuthouse!) would replace NAS, thats not the case. CASPIAN is only a platform.
The Flight Data Programme Replacement (FDPR - Project 1843) originally envisaged a replacement with collaboration from Europe and a rollout in 2007/8. However, as at last week, the plan is to re-engineer changes to NAS with a rollout in 3 years time.
Not quite sure how this fits in with the move of NAS out of West Drayton to either LACC or Tech Centre though.

[BEXIL160]

Thanks for that. As ever far more (useful) info available here on PPruNe than from the company itself.

Rgds BEX

[Minesapint]

I did say CASPIAN was the plan - not that it would or could replace NAS.

Although there are those out there that may not agree with me, NAS is a truly excellent system. A single NAS is designed to propel a single centre - not four. We often think that we have squeezed about the last drop of blood out of the old girl an then we add even more. It just shows how excellent the original design was. The people who designed it were truly gifted.

Its also rubbish to say that the software is 30 - 40 years old. Software does not grow old. It is only replaced by something better. Hence we still have NAS cos there is nothing better.

NAS software is (mainly) written in a language called JOVIAL. JOVIAL is still used is flight management systems - C17 Skytruck to name but one 'old aircraft'.

If it aint broke don't fix it..... :)

[BDiONU]

Not saying NAS is poo, as stated it does a remarkable job for which it was never designed.
However Jovial is a very old language and can induce errors which cannot be trapped by error checking, 'cause there's no error checker for it! So its LONG overdue to be dragged kicking and screaming into the 21st century. For my preference into an object oriented language so we don't introduce regression into areas where no change was made.

[Scott Voigt]

Minesapint

There are a lot of reasons to dump NAS. Not to mention being able to program in something modern that doesn't take forever to make a useable change. The kernal that started out in the IBM 9020 all those years ago, was GREAT at doing what it needed to do on 80 K of core memory. However we have grown past that and there are indeed needs to be able to get way past what NAS was designed to do, and what it is design limited to do.

Why have all of your eggs in one basket per se? You lose one function with in NAS now, and you lose them ALL. Go to a distributed system so that if one bit goes bad in a program, all you lose is that one function, not the entire program.

You also want to be able to start tying in newer functions to the software and not have to continually rewrite the host software to accept things. Coming off of a 30 year old platform is a good thing... Now, just taking the old software and rewriting it is NOT in itself a good thing... For some of the above stated reasons.

Shoot, if you folks want NAS that does a LOT of stuff as is right now, we could sell you ours rather cheap <G>.... Soon to be getting interactive data blocks that interact from sector to sector as well as center to center. I don't just mean altitude changes either. We are going to be getting a fourth line in the data block which will give us a scratch pad ability if we need it, but will also have a way of passing speeds and headings ( not supposed to tell the pilots to do that sort of thing) we are also looking at the time share of aircraft type and other info...... Soon to have input stuff between the URET conflict probe and the radar glass...

regards

[BDiONU]

Thanks Scott, another (and better!) reason for going with an object oriented computing language. Only the part of the programme with the 'problem' would fail, not the whole thing as happens now!

[Minesapint]

All agreed. As long as its as good or better than the system its replacing and is as upgradable. (30 years worth at least).

Putting 'new' code into pretty grey boxes may suit many but if it don't work in the first place don't bother.

I would appreciate information on any COTS system, available now, that has at least the current capacity to shift 2 million movements with 4 centres ( 2 en-route, 1 sub-centre and one TMA) and has the capacity to handle 4 - 5 million? I have said this before. Let the US spend the money deveopling a new system then buy it. ONCE ITS PROVEN!:)

[atco-matic]

Getting back to the topic, wasnt there a procedure that came in a few years ago when we were still at LATCC for times when we ran out of codes? I seem to remember that the letters SATN would be printed on the pending strips instead of an allocated sqwawk... if we saw this happen we were supposed to run to flight plans and tell them, and manually unpair sqwawks on aircraft that had left our airspace, so that the codes could then be reallocated a.s.a.p to aircraft waiting to depart (which could not depart until they had been allocated a sqwawk)... was this not the case or am I just imagining it? What happens now we are at Swanwick where we don't have pending strips? Is this procedure still in? How do we know if the system is running short of codes?

I seem to remember this coming in about the same time as those awful ''half strips'' were being banded about... do you remember? Those strips that had different fonts and would be printed in half the time as normal strips when it was busy cos the dear old printers couldn't get them out quick enough... only thing was they looked awful and had crap fonts on them... hmmm sounds familiar!!! Never saw any of those operationally either...