Mode S
 

I know it's hopefully a way away yet and hopefully may yet be headed off at the pass but in anticipation I am interested in what we may be letting ourselves in for.

I gather there is only one suitable unit available yet for light aircraft - around £2.5K - £3K. Not being an avionics expert however I wonder what else is involved. I gather mode S will, in addition to altitude information, provide a unique identity and heading information. Presumably the call sign is programmed into the unit - not a big problem I guess, and the altitude provided in the came way as the current mode C units - also integral to the transponder. What about the heading though? Does this mean connection to the DI and potentially also having to fit new and compatable DI, or is heading information sourced in some other way? I am always concerned about the headline price of these units because this can be so misleading if other changes to the avionics panel are required so that the fitting / conversion costs end up being as much again!! Am I correct that the only additional information mode S provides is call sign and heading?

I would also be interested to know whether controllers feel mode S equipted light aircraft would help them, and whether their answer would be different depending on whether the aircraft was operating IFR or VFR. Finally, will both radar control zones and LARS units be equipted to interogate mode S transponders or only radar control zones. Presumably if the latter, mode S will be sod all good in open FIR!

I think the short answer is "nobody knows". The cost will be a lot more than £2.5k, that's for sure.
And I've heard said that all GA will have to fit them, then that the ATC computers will be programmed to ignore all GA not flying airways.

So we'll all blow a few thousand for nothing.

What me - cynical? Never!

or its a way for G Brown to charge GA for services rendered. cynical...moi?

If you're not in conttroled airspace you don't need it. If those that use CA insist all have it, even those outside CA, then it's for their benefit and they should pay.

SSD

Whilst doing my PPL skills test I put on the transponder in mode C + ALTitude, as I would rather be 'seen' by any TCAS equipped aircraft in the vicinity and feel that information such as altitude, if available, should be given. Although I was not in controlled airspace I was underneath it.

At the test debrief the CFI said it was preferable not to give altitude information when flying below or near controlled airspace (unless specifically requested by ATC) as anything heavy passing overhead has the 'inconvenience' of changing autopilot mode to a vertical speed mode when they pick up your altitude data in the traffic advisory. If you are close enough you could also of course generate an RA which would be even more inconvenient for the Jet-A1 guzzlers !

Its no coincidence that the CFI is a jet jockey himself!

:rolleyes:

Sorry Simjock but that is absolute b*****ks. The TCAS has no effect or autopilot mode in anything that I have flown. The main difference between Mode A and C returns as far as TCAS is concerned is that an A return cannot be 'resolved'. TCAS is only able to offer vertical guidance (at present) and therefore if a 'threat' has no altitude data attached to it it will only be shown as 'proximate' traffice i.e. "Watch out buddy, there's a plane over there"

The TCAS system filters out (dependant upon mode selected) aircraft that present 'no threat' which are separated by at least 2000'. The system still looks at all of the returns and assesses closure rate and conflict liklihood based on a little protective bubble around the a/c called a Tau. When a threat is first encountered it will be observed usually as a yellow circle with accompaniny altiude difference and the aural "TRAFFIC" message. The next phase is a full RA or Resolution Advisory where the climb/descend instructions are given. Ergo the system works on closure rate. If you are outside of the Tau and no accelerating towards it there will be no message.

Main point: Without altitude data the system cannot resolve a conflict nor can it filter 'unwanteds' out. The system reverts to a safe option of announcing the altitude-less threat with "TRAFFFIC". This means that on a busy Saturday one can be flying around with "TRAFFIC TRAFFIC" harping on. If you have altitude reporting and you intend to use your transponder, turn it on.

Cheers!

From an ATC point of view: Always select Mode C if you have it, and especially if you are near CAS. We need as much info as possible on you to ensure you do not pose a threat to other traffic. Many is the time I have had a/c reporting a TCAS TA and the only thing in the area is a 7000 squawk with Mode A only. The only reply we can give is that there is traffic in the area which is BELIEVED to be outside CAS. If you have Mode C the TCAS will not shout unless you really are a conflict and we can see what the situation is (although technically we are not allowed to base separation on your Mode C unless it has been 'verified', which means gettting a level report and checking it with the radar).

There was a debate about six months ago about Mode C in which some people suggested they didn't like putting it on because it meant ATC could see that they weren't maintaining a level or because if they were close to the base of CAS they might wander into it and didn't want to be caught. If you can't maintain a level when requested then you should go and have a few more lessons, and if your attitude is the latter then you shouldn't have a licence!!

Mode S: For a commercial aircraft then I think it is a good thing. We are already short of squawks and there has been more than one occasion of misidentity due to selection of somebody else's squawk. In one dase two aircraft from the same airline flew all the way from Scotland to London on each other's squawks and the ATCO couldn't work out why his instructions were not working! It was only when one of them ended up near Brize instead of WCO that the penny dropped. What I am not clear on is whether we will also ne able to work with non Mode S squawks in the airways from people such as Fuji. I imagine we will, but haven't checked. As you say, £3000 for a C172 who goes airways occasionally seems a lot of money.

It's not just the cost of the unit. There are plenty of aircraft in the UK with no electrical system and not just gliders. They rely on hand held radios or a lightweight battery to power a simple installation. There are very few transponders that draw sufficiently low power to operate with this kind of system let alone Mode S ones.

I have seen a Tiger Moth with a transponder fitted but it was very much the exception in this class of aeroplane.

As I understand the current situation approximately 50% of registered aircraft in the UK are microlights. Where the hell do you fit a transponder on a weightshift machine? :confused:

I always fly with the txpdr on Mode C. Seems stupid not to if you have it....after all its my ass up there !

I was a bit surprised when first flying in the UK, coming back into a class D zone in the south of England, the instructor I was doing the check out with told me to turn off the txpdr as the ATC "didn't like all the 7000s all over the screen!"....seemed a bit alien to me, especially after flying around the LA basin where air traffic is about 100 times what it is in the UK.....

The thread that "eyeinthesky" refers to was placed by me. I did so to request that pilots of mode c equipped aircraft use it as advertised in order to avoid generating false TCAS alerts to other aircraft.

Unfortunately it was used as a medium by a few puerile so-called pilots to throw rocks, accusing me of wanting to close down airfields, stop GA altogether and to to catch other pilots out for committing their minor flying indiscretions.

Such is life. :rolleyes:

Search for:

"Please also use mode c when transponding 7000!"

(dated 22 March 2001, on this Private Flying thread).

[ 15 December 2001: Message edited by: Skycop ]

To reinforce the comments of those above, IMHO the advantages of a conspicuity code with Mode C far outweigh the disadvantages.

To quote from the UK AIP ENR 1.6.2. - SSR OPERATING PROCEDURES:

1. General

1.3 With the exceptions detailed in paragraph 2 pilots shall:

(d) Select Mode C simultaneously with Mode A unless otherwise instructed by an ATS unit;

2.2 Conspicuity Code

2.2.1 When operating at and above FL 100 pilots shall select code 7000 and Mode C except:
(a) When receiving a service from an ATS Unit or Air Defence Unit which requires a different setting;
(b) when circumstances require one of the Special Purpose Codes or one of the other specific conspicuity codes assigned in accordance with the UK SSR Code Allotment Plan as detailed in the table at ENR 1-6-2-3 to ENR 1-6-2-6.

2.2.2 When operating below FL 100 pilots should select code 7000 and Mode C except as above.
+++++++++++++++++++++++++++++++++++++++++++

The only time that the transponder should be selected without Mode C is when instructed by ATC or when the Mode C is u/s. Any instructor who tells you anything different is wrong and is probably not the best person to learn from. Consider changing to an instructor who knows his job.

Exactly Rolling Circle::

Any instructor that does not understand transponder mode C position reporting is three dimentional shouldnt be instructing.

And for shure does not understand the word " safety "


.................


:D The hardest thing about flying is knowing when to say no. :D

Thanks for all the advice, I shall continue my Mode C squawkings wherever possible.

I think the autopilot mode change bit is perhaps a matter of Company procedures.. if one is in say Nav mode, perhaps SOP's dictate a V/S mode if you get a TA ? RA's usually require autopilot disconnection anyway so do not apply.

Anyone in the know?

I think that this mode S protest is a bit of an over reaction from AOPA as it is clear that the JAA has not the first idea of the technical problems introduction.

Mode S is only of eny benifit if more than an SSR reply and alititude are transmited , the mode S should also transmit HDG and IAS.

Apart from the power supply issue how is the mode S transponder going to get the IAS and HDG imformation as this is required in a digital format ? has your aircraft got a digital pickoff for these systems ? i think not !.

As i fly IFR some of the time i have had to give some consideration to all this and and have held off from fitting the latest very cheap JPI fuel flow transmiter because it MAY get in the way of the most likly mode S instalation.

At the moment the best way of getting the digital output for the mode S is the Shadin fuel/air data computor apart from the fuel flow it takes the HDG imformation from the HSI bootstrap (28VAC/400HZ power required)and pitot/static from the aircraft system and it also has a OAT probe and converts this to a digital signal for the mode S HDG ALT and IAS modes.

The up side to all this is if you have a good panel mount GPS (king KLN90 / 89B and most of the garmin IFR units)this can intigrate into a system aproching the capabilitys of an modern airliner FMS system giving you imformation on actual wind speed and direction , TAS ,fual burn to waypoints,and more acurate altitude imformation for the APP mode for the GPS and all this via the screen on the panel mount GPS.

As you can see its a powerful system but it is also utterly impractical for most light aircraft that the JAA could not insist on it because without the aditional imformation from the ADC it has no benifit over mode C.

Simjock, probably a company thing. In mine, we only respond to RAs, a TA only requires a good look out in response. There is no autopilot which will automatically respond to either a TA or RA.

And as for those who don't squawk when able - please do! Flying outside controlled airspace level a thousand feet below another aircraft in the airspace will only generate a TA (even Mode C against Mode S), which will prompt a better lookout in that sector.

A and C. I was searching for something on Mode S and found this old thread. I think it's worth ressurecting cos a lot of people have their heads in the sand over the introduction of Mode S (and I'm bored :) ).

I for one didn't realise that the Mode S is supposed to transmit HDG and IAS in a digital format or otherwise. Well that effectively prevents it being fitted to 60% plus of the aircraft registered in the UK then. <img src="rolleyes.gif" border="0">

Excellent plan messers CAA, what are you going to come up with next? <img src="confused.gif" border="0">

I,v not got to the bottom of what the exact data that will be required by mode S but it seems that it will be along these lines aircraft ident , ALT ,IAS or TAS , HDG (track ?).

As soon as i can I,m going to get hold of the installation manual for the King mode S transponder and look as the interface options it is only then that I can evaluate the true impact of this on the private end of the GA market.

The digital input that i refered to in my last post on this subject is to get the data into the mode S unit from the aircraft systems for exampel the most common remote compas system in GA is the King KCS 55 and that,s HDG output is an anolog syncro system that has to be converted to a digital system even for King gps units to give a "HDG up" map display.

The bendix king web sight for europe shows the new mode S unit so the technical data shold not be to long in showing up but i dont place much faith in the glossy sales handouts as the sales people tend to hype up the product (To be fair king less than most)but as with all these systems the devil is in the detail and you will only find that in the technical manuals.

[ 14 February 2002: Message edited by: A and C ]</p>

A and C, my navigational / positional equipment consists of:

ASI. .P11 Compass. .Altimeter

Oh yes, and a PilotIII GPS :)

Unless the Mode S transponder manufacturers come out with a unit that a handheld GPS can connect to then 99.9% of the GA fleet is not going to be able to supply the data the unit requires. Alternatively, if they come up with a unit that has a built-in GPS and a colour moving map, more people might take less convincing that it is a good idea.

L&S i dont think that you should worry about mode S as once the practical realitys of implimentation for your type of VFR flight surface then it will all get just to hard to do and the burocrats will go and find some other poor sods to bother.