Controllers, how do gliders show up on your screens?

[mary meagher]

In Holland, they required all gliders to carry and use transponders, which so cluttered up the screens they then asked them to restrict use. Do you think gliders should use transponders?

Can anyone in your line of work tell me how do gliders show up? Especially traveling in gaggles? Enroute controllers, how do you warn traffic using your services about these plastic hazards behaving in strange ways?

Right now the gliding folks are all bent out of shape because the Junior Nationals endangered a display by the Red Arrows over Silverstone, which had to be cancelled. This is being discussed at length on Private Flying forum, where a Dutch glider pilot contributed information about their local requirements.

I would be very interested to know your opinions.

[eagleflyer]

Thermalling gliders are usually filtered out by the software because they have virtually no groundspeed. A glider that is quite close (say 30 miles at reasonable altitudes) to an antenna will usually be displayed as a primary target (just a little cross) that´s moving veeery slowly.

These primary targets are easy to miss on a busy day and working with a large scale.

I think that a transponder should not be mandatory for gliders. They are very useful though in some cases though, especially around airfields without protected airspace for IFR-traffic like Niederrhein near the Dutch/German border or a couple of military airfields. Flying in the middle of nowhere you don´t necessarily need a transponder.

What happens on nice weekends is that the 7000-codes will be put into a code-filter and only be displayed in a dimmed colour so that you will still be able to see your IFR-traffic.

[orgASMic]

Using a short range radar at an airfield (ie out to about 40nm), they show up pretty well as primary contacts but not all the time. The return will tend to twinkle as the glider manoeuvres due to large changes in the glider's aspect to the radar head and its ground speed.

Transponders in gliders would be of use when they are operating in small numbers but only if they had Mode C. They would be of no value during mass competition launches; the overlapping labels would just cause ridiculous clutter.

[chevvron]

Gliding competitions in the UK often involve up to 100 gliders; if all these used transponders it would mean the radar display being unnecessarily cluttered.
As far as primary radar goes, if it's 'raw' primary with MTI, you would lose the blip every time the glider circles in a thermal as its turn takes it tangential to the radar (tangential fade = zero apparent groundspeed); if using processed primary with an adaptive MTI system, it would depend on the threshold speed of the MTI, this being the groundspeed below which all returns are filtered out, usually 50kts but tends to vary according to user requirements.

[Lon More]

EagleFlier the problem comes, as Eurocontrol discovered last week, is when there are so many squawks that the track server is saturated and then just rolls over. It is possible to suppress them but this only happens after initial processing has taken place. It would be easier to filter them out using mode C info but this would often require making an expensive bit of kit that adds nothing to the enjoyment of gliders/ultralights compulsory. As most of this traffic doesn't venture or isn't allowed into the upper airspace the conspicuity codes are unnecessary as far as I was concerned however they are essential in the lower airspace as, despite the almost universal use of GPS, airspace infringements continue to be a problem.

[PeltonLevel]

At least the CAA doesn't appear to have mandated carriage (and, presumably, operation) of transponders throughout UK airspace for all types of aircraft!

http://www.caa.co.uk/docs/1/Mode%20S%20decision%20-%20In%20Focus.pdf

[Jagohu]

Lon More: the cause of the problems wasn't the number of squawks, but the fact that a short plan was made on a VFR squawk (erroneously having a Mode C of FL601) and due to their large numbers, this input has overloaded the correlation logic that didn't know which one to couple the short plan with - then it all went down.

I think the problem here (NL, BE, W-Germany) is the lack of "middle of nowehere" airspaces - wherever you go, you'll bump into a TMA, CTA, MTMA, TRA rather sooner than later.
I don't think Mode-S transponder is a solution for gliders either, but as a matter of fact they are a clutter also when they appear only as primary targets - and those ones are much more frightening for me than seeing that it's A7000 - at least from that I know that even if it hasn't got mode C it's somewhere "down below" our airspace.

[Lon More]

Thanks Jagohu, that's a new one

but the fact that a short plan was made on a VFR squawk (erroneously having a Mode C of FL601)

The old problem. When you think you've built an idiot-proof system someone builds a better idiot.

[mary meagher]

Thanks, guys, I really appreciate your information!

When Upper Heyford was still active, they invited local fliers for a tour, including the radar room, and they impressed us with the radar view of road traffic on the M40!

I was towing a glider back from Booker (Wycombe Air Park) once, with a Piper Supercub in a fresh wind, making a ground speed of about 30 knots, which apparently made it difficult to see on radar. Anyway, I did talk to them, and they kindly informed me that a couple of F111s were about to do a maneuver abeam, which was so interesting (sort of a Red Arrows flypast)
that I lost my concentration, and next thing, the glider on tow was also abeam!

Didn't know what to do, so did nothing, and the glider pilot sorted it out by opening his airbrakes. It took us well over an hour to get back to Edgehill!
Ah, those days are gone forever!