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Correlation between weekend flyers and Mode A transponder use

This seems so overwhelmingly obvious, when flying around with a TCAS system.

On Sunday I did a little scenic local, Shoreham, around the Isle of Wight, and back. Loads of Mode A targets.

Are there really so many planes which have specific old Mode A – only transponders? Or do many pilots turn off Mode C?

Administrator
Shoreham EGKA, United Kingdom

Maybe the mode-C interrogations from you aren’t seen as easily by other transponders as your mode-A interrogations?

ESTL

Why would this be much worse on weekends?

Administrator
Shoreham EGKA, United Kingdom

No idea. But you are quick to conclude that people either do not have altitude reporting transponders or turn it off. I am just trying to take a broader look on the issue that you see few mode-C returns on your TAS-box.

Maybe your TAS equipment has trouble to map mode-A returns with the corresponding mode-C return to get both code and altitude?

ESTL

In a radar environment transponders are triggered by the ground station anyway….so I would have thought detection does not rely on active interrogation from the TAS….i.e. passive detection should be adequate…

EGPD / OMDW / YPJT, United Kingdom

An active TCAS system uses returns from its own transmission only. It could not measure the distance otherwise.

Administrator
Shoreham EGKA, United Kingdom
In a radar environment transponders are triggered by the ground station

AIUI, you may leave out the radar environment bit – traditional transponders, up to and including mode S, will only transmit when triggered.
That is (if I have things right) the one difference to ADS-B, European style: such a transponder will transmit data packages, similar to mode S, periodically even when not triggered. To the delight of FlightRadar24 and the likes – and many more who prefer to remain unnamed and unmentioned.

And yes, to me it seems obvious the opening suggestion is right, or at least it might well be right round here though I am not acquainted with the UK situation: many pilots do have a transponder available, but activate as little of its functionality as they can. None will say so publicly of course, but I am sure this is deep into the PPL culture round here, and even deeper among (a certain subgroup of) ultralight pilots. My reading is that they judge the disadvantages (for themselves) more important than the advantages (for others). Leaving frustration with ATC and FIS staff.

EBZH Kiewit, Belgium

That is (if I have things right) the one difference to ADS-B, European style: such a transponder will transmit data packages, similar to mode S, periodically even when not triggered. To the delight of FlightRadar24 and the likes – and many more who prefer to remain unnamed and unmentioned.

FR24 sees both Mode S and ADS-B aircraft, though it may see ADS-B ones (currently, almost nobody in light GA) a bit better, and should see them much more accurately.

Sure a lot of people don’t want to be seen, but turning off Mode C is going too far. Mode C reveals nothing about the individual aircraft. Turning it off does enable you to bust CAS from underneath. It also makes you invisible to commercial TCAS 2 systems… so when you are busting CAS you are all the more likely to hit something big.

The Mode A returns I see are nearly always “proper” powered aircraft, which is why I question this. I didn’t think there were many Mode A transponders still installed… maybe someone running an avionics shop might know?

Maybe your TAS equipment has trouble to map mode-A returns with the corresponding mode-C return to get both code and altitude?

I don’t know if that is possible. Doesn’t the altitude come back in the same (longer) packet as the squawk? @tomjnx might know this stuff.

Administrator
Shoreham EGKA, United Kingdom

I suspect there are very few mode A only transponders still around these days (I have never even seen one )

When secondary Radar installations began to become more prominent, I believe there was a certain initial reluctance ( for PPLs especially) to squawk mode C, (even one of my flight examiners deselected it because he “didn’t like to be watched”) but these days I would have thought that since the widespread installation of mode S units, the reasons for not squawking mode C are now pointless and that it has therefore become less of an issue.
I find Peter’s observations are therefore a little surprising.

Egnm, United Kingdom

If you do not want to be seen, why turn the transponder any further than STBY anyway? Mode A make more harm than good because ATC are forced to give traffic information (or even avoidance) about such traffic which may be vertically separated by several thousand feet. I am not sure how smart it is to fly underneath a TMA transponding mode A.

I would need to dig into AIPs to check that, but I was under the impression that pilots were asked to turn on Mode C or nothing.

LFPT, LFPN
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