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-   -   Mode S: do we need it in GA? (https://www.pprune.org/private-flying/561180-mode-s-do-we-need-ga.html)

300hrWannaB 9th May 2015 22:19

Mode S: do we need it in GA?
I fly a group owned touring plane, and we are having a discussion (about money) and whether we really need to upgrade a perfectly serviceable Mode C to a Mode S.

One or two members have IMC rating, in fact one is progressing to PPL-IR.
The rest of us are VMC only, but like to know where we are.

Having tried to understand the rationale, I am still struggling to see why, or where, we would need Mode S. Apart from local flights in SW England/Wales, the typical routes include Lancashire, Ireland, Channel Islands, France and the near Continent. The furthest we have been is Switzerland. It's 99% UK.

I'd like some input, but please be clear about the difference between opinion and fact.

dublinpilot 9th May 2015 22:27

No mode S needed in Ireland for VFR. No plans for introduction either.

Talkdownman 10th May 2015 00:22

Opinion: For PRIVATE aircraft Mode S is an infringement of PRIVACY.
Opinion: Mode S should not be necessary for flight within UK uncontrolled airspace.
Opinion: Mode S does not enhance flight safety outside controlled airspace.
Fact: Mode S is not even required in the London CTR.
Opinion: If your aircraft will not fly within airspace requiring Mode S don't bother with it. Apart from the spotters, who is going to be interested in your reg and any other downlinked parameters? Save your money and stick with A+C for ACAS safety.

Johnm 10th May 2015 06:28

Mode S and ADS-B will be a requirement for IFR flight in controlled airspace in a couple of years and so your PPL IR member may be a bit stuck then. I would wait until the requirement is introduced as there are product developments in the pipeline that may be cost effective.

Maoraigh1 10th May 2015 07:29

Mode S is very useful on our Jodel DR1050. ATC can see the callsign. I've been called "Are you on our frequency yet?" when returning, as soon as I appear on the radar. Fewer radio requests for position reports.

tomellis6680 10th May 2015 07:50

I'm currently in Prague LKPR on a European trip, most larger TMA's in Europe are adopting a Mode S requirement to be able to fly VFR in their airspace. That's why I find it useful as it gives me the 'go-anywhere' ability without having to trawl information about specific aerodromes requirement for fly in VFR. If you're just flying in the UK then it doesn't matter too much but it doesn't mean that the UK won't start implementing the Mode S requirement in the future.

Jan Olieslagers 10th May 2015 08:33

Adding to previous: some countries require mode S for almost all flying. For one example the Netherlands airspace is all TMZ above 1200'. Not that it matters much, the Netherlands is generally not an attractive destination anyway.

Yet it really depends on where you wish to fly.

Rod1 10th May 2015 10:16

In the UK TMZ - Transponder mandatory zones - are becoming more common. If you have mode s you can ignore them if you have mode a/c you have to get permission to enter which can be a pain.

I find I get clearance through CAS more easily now I have s over my old a/c - same aircraft.

Mode S is becoming steadily more important in Europe with different states having different rules but it all slowly getting harder to (a) know the differences and (b) fly without s. France is considering changes which may require mode s in class D but this is not a done deal.

In the medium term it is likely that Mode S combined with ADS-B will give considerable advantages for collision avoidance and airspace access. Avoid the Garmin range of units as these will not do Extended Squitter without spending silly money - if at all. Almost all other units will.


The Ancient Geek 10th May 2015 10:22

There is a simpler answer.
If you need to fit a new transponder go for Mode S to avoid having to buy another in a few years time, they are gradually becoming required in more places.
If you already have Mode C dont bother upgrading until you actually need it because they are getting cheaper.

Jan Olieslagers 10th May 2015 11:14

Mode S is becoming steadily more important in Europe
That is certainly the trend we have seen over the last few years. With EASA promising to have more attention for the situation of g/a and recreational flying, couldn't this trend be reversed, or at least slowed down?

@The Ancient Greek: such would be my recommendation, too, if only it were clear where the plane is intended to fly. If a good part of flights are to the continent, it might be more urgent.

Bigears 10th May 2015 13:04


Fact: Mode S is not even required in the London CTR.
I respectfully suggest that you are incorrect in your assertion.
UK AIP GEN 1.5 Para 5.3.1(b) & in conjunction with the ANO Schedule 5 paragraph 3(6)(b) would appear to state otherwise :8
Happy to be convinced otherwise :p

lasseb 10th May 2015 14:36

Just to clarify for talkdownman (and maybe others)

First, the simple mode-s that is required for private small planes does not really send that much downlink data, besides altitude, squawk and transponder ID (ac reg).
It is not required to send position or any related parameters.

Secondly, the mode-s protocol is much better and contains both better bit encoding and checksums. This leads to less mistakes in decoding, which leads to better TCAS and better ATC awareness, which leads to better safety for everyone.

I would go for mode-s any time...

Private jet 10th May 2015 16:07

Mode S is hardly new, its been around for a quarter of a century now! I'm always amazed at the reluctance to accept new technology once it has be proven to be reliable and of benefit. I can only imagine its that old chestnut of cost making people reluctant to use it.
As stated above mode S is basically A+C with automatic aircraft ID as far as ATC are concerned. In the air its function extends to the aircraft collision avoidance system, a very reassuring bit of kit to have I must say, having had it in my professional life. The more aircraft 'S' equipped there are, the better things are, especially when venturing into "no mans land" outside controlled airspace! ADS-B is the system where there is downlinking of more data for tracking purposes (present position, track, ROC/D etc. etc.) Not sure why that's a privacy issue for private flying though.

Jan Olieslagers 10th May 2015 16:28

amazed at the reluctance to accept new technology
The price ticket is perhaps not an issue to you? That makes it easy to be amazed. But no, it wouldn't, to anyone who can afford a Private jet. There are some private flyers around, though, to whom cost is more than a chestnut. Thanks for your consideration.

[[edit]] adding the cost of having to upgrade comm's to 8,33 in the near future, nobody's waiting for another mandatory avionics upgrade.

Talkdownman 10th May 2015 16:59

Originally Posted by Bigears
UK AIP GEN 1.5 Para 5.3.1(b) & in conjunction with the ANO Schedule 5 paragraph 3(6)(b) would appear to state otherwise refers only to the London TMA.

TMZ exceptions are detailed in GEN1.5 paragraph 5.3.4, AD-2 EGLD, AD-2 EGTF, AD-2 EGLM, AD-2 EGWU and for Brooklands see EGLL AD 2.22 paragraph 8.

eg. AD-2 EGLD:

Mode S Transponders:
(i) The carriage of a Mode S Transponder within the LFA is encouraged, however there is currently no requirement for aircraft operating in the Denham LFA to comply with the requirements of the London CTR Mode S Transponder Mandatory Zone (TMZ).

Bigears 10th May 2015 20:08


I apologise for my mistake ref

If I may be so bold, I would think that your original statement
'Fact: Mode S is not even required in the London CTR' should have read
'Fact: Mode S is not even required in some portions of the London CTR', as that is more factually correct.

Thanks for the references, which were an education for me :ok:

Talkdownman 10th May 2015 21:20

Conceded. Shake on that.

300hrWannaB 10th May 2015 22:31

Thanks for the inputs so far, please keep them coming.

Of prime concern is the cost of the upgrade, considering that the Mode C is working just fine. The other consideration is that we are going to change the radio (yes we still have one) to an all singing & dancing GPS type navcom on 8.33 separation. That's a bit of a sting.
Doing the Mode S at the same time seems logical, if money were no object. However, the money pits are not bottomless, and the old girl has some other repair/maintenance priorities to be addressed.
All I'm trying to do is to establish the priority ranking of a Mode S.

-Netherlands are now restricted to Dambuster style bombing raids at low level (watch for the pylons!)
-SOME London TMA remains accessible, ie to nominated airfields on the margins.
-The creep of EASA regulations will likely lead to its expectation. Charge the GA flyer, yet benefits accrue to the other users ie ATC and jets.

My query remains one of restrictions and access.

A le Ron 10th May 2015 23:20

When is the requirement for ADSB likely to come in? That wil be yet another expense, having recently upgraded my unreliable Narco mode C to a Garmin mode S (at the suggestion of my engineer).

chevvron 11th May 2015 03:47

Answer to original question:

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