Peter wrote:
It also seems clear that in Germany there is a big cross-subsidy from airlines to GA, which in the UK would cause a lot of trouble.
The same thing happens in the UK. Most GA does not pay IFR enroute charges. Most of that is paid by the airlines which funds NATS. Light GA uses ATC in the UK for free.
I can’t agree that the system in UK is ‘ridiculous’ as stated in post #2. There’s very little that’s funny, or worthy of ridicule, in this situation.
What I do believe is that the UK situation is amateurish and not fit for purpose. It’s also widely believed that ATC in UK is not cheap compared with FAA land.
The small and fragmented cells of ATC coverage, the frequent refusals of ‘traffic service’ and the nonsense of the ‘Basic service’ all serve to put UK VFR pilots outside the envelope of Radar protection. This may be the reason why the UK is currently enjoying the emergence of a plethora of proprietary collision avoidance systems, all well intentioned in themselves but all trying to cover up for the total absence of what should be an essential public service, Flight Following*.
*For anyone who is not familiar, Flight Following is a discretionary but rarely refused service available to VFR pilots in the US (subject to radar coverage) that provides a single squawk for an entire trip and and synchronized handovers en route. While much of the traffic called does go unseen as stated earlier, in my experience any conflict is followed up with repeated advisories and suggested avoiding actions.
Sadly, you can even see a little of the UK Mk1 eyeball mentality in what the airprox board term “the late sighting” by the C42. At a closing speed of several hundred knots and constant aspect, I regard that as a good effort, probably better than would occur in the majority of situations. The fact is that collision was avoided by an early (or timely) sighting, not a late one!
Lastly, the TCAS failure must surely be worthy of investigation.
Light GA uses ATC in the UK for free.
Agreed, but also there is total resistance to going any further, specifically total resistance to going beyond ICAO FIS obligations.
I’ve just read the airport report. I find nothing there notable but as Aveling says
The pilot of the C525 reported not having seen the C42, nor receiving any TCAS alert, although TCAS II was reported fitted to the C525, and both aircraft were transponding SSR Mode A & C.
should be investigated. However, as I have often reported here, light GA (not bizjets) often shows very late on my Avidyne TAS605. I assume this is due to crappy transponder installations, combined with my installation having less that claimed sensitivity at the 12 o’clock bearing due to the roof curvature. However I see all jets up to the claimed 15nm on all bearings… That C42 ought to have a proper radio check done.
Peter wrote:
However, as I have often reported here, light GA (not bizjets) often shows very late on my Avidyne TAS605. I assume this is due to crappy transponder installations … That C42 ought to have a proper radio check done.
Remember that most light GA will have one transponder antenna, on the bottom. This is the perfect location for the primary interrogator of transponders (ATC radar on the ground). However, if you’re above or even level with the other aircraft, their transmission will be attenuated by airframe parts.
Jets have transponder antennas on the top as well as underneath. The C42’s transponder is probably working perfectly well and is not in need of a proper radio check, as evidenced by ground radar being able to track it just fine. But without imposing the expense of a dual antenna installation on every aircraft owner, you’re just not going to get the range on your Avidyne that ground radar will since your antenna is on the top, the other guy’s antenna is on the bottom, and you like to fly high so are probably above most transponding traffic – with the signal having to pass through two airframes before reaching your antenna.
I would not think that is an issue at a distance, however, when the altitude difference represents only a tiny angle.
Discussion with the C42 pilot whilst flying a, possibly the, C42 here…
Interview with the C42 student here…
Peter wrote:
I would not think that is an issue at a distance, however, when the altitude difference represents only a tiny angle.
Distance (inverse square laws) and now the line of sight slants through each airframe presenting a lot more metal between your antenna and their antenna, plus an antenna radiation pattern that’s at least a few degrees down will certainly have a very measurable effect, I would have thought!
The only good information on transponder radiation patterns with 1/4 wave stubs I’ve found is this: page 21 and on, and it’s for an antenna mounted on top of a Cessna 172, so turn things upside down to get a feel for what the pattern looks like with a typical bottom mounted antenna.
http://calhoun.nps.edu/bitstream/handle/10945/32613/98Dec_Calusdian.pdf?sequence=1 [ local copy ]
Significantly: “Underneath the aircraft, the radiation exhibits sharp peaks and nulls with the peaks being approximately 10 dB below the maximum value (5.0 dB for this plot). However, adequate coverage below the aircraft can not be expected with the antenna installed at this location.”
The diagrams also show that depending on the exact location, the signal can quickly get attenuated when you’re on the wrong side of the aircraft (which for a typical installation on the bottom, there is already significant attenuation horizontally from the aircraft). To make matters worse for you personally, with your TCAS antenna on top, you’re actually combining the worst of both worlds when you’re trying to look out for a GA plane with only a bottom mounted transponder antenna!
Interesting… thanks for finding that.
There are other factors.
Most GA TAS/TCAS installations have two antennae; one above and one below. One resolves left/right and the other resolves front/back. You can install them either way round. I think this is the case for both Avidyne and Garmin products. I would think Avidyne are more numerous simply because Ryan/Avidyne have been the main player for a long time. It seems obvious that the software blanks out a target when it is seen by one one of the two antennae, but by then it will be really close, or has already hit you.
A target which is far enough above or below to mask its antenna from you is also not going to hit you – unless there is a climb/descent taking place as there was in this case.
Silvaire wrote:
That’s arguably negligent but pragmatically true – If I see an airliner or other jet in (say) Class E airspace I assume they are not watching for traffic as they should, and that ATC may not call me as traffic for them.
Interesting point you are raising there. Here is a quote I can never get out of my head (from http://www.flv.dk/milais/flyingindenmark/flying%20in%20denmark.pdf page 3):
Between 3500 ft MSL and FL 195 (Class E) VFR flight may be conducted without clearance from ACC Copenhagen, but only with ‘Traffic Information’, i.e. the pilot must be in two-way radio contact with a radar unit (ATS or ACU) and receive traffic information. Under all circumstances the pilot must ensure a separation to civil IFR flights of minumum 5 NM horizontal or 1000 ft vertical. (This is very important – triggering somebody’s TCAS will result in a report from the civil aviation authorities!)
How the hell can you make sure that you don’t trigger somebody else’s TCAS? Like in the scenario described in this thread. The C42 had no chance to see the Citation Jet before the last seconds, and it was just a coincidence that the TCAS was not triggered.
Dimme wrote:
Between 3500 ft MSL and FL 195 (Class E) VFR flight may be conducted without clearance from ACC Copenhagen, but only with ‘Traffic Information’, i.e. the pilot must be in two-way radio contact with a radar unit (ATS or ACU) and receive traffic information. Under all circumstances the pilot must ensure a separation to civil IFR flights of minumum 5 NM horizontal or 1000 ft vertical. (This is very important – triggering somebody’s TCAS will result in a report from the civil aviation authorities!)How the hell can you make sure that you don’t trigger somebody else’s TCAS? Like in the scenario described in this thread. The C42 had no chance to see the Citation Jet before the last seconds, and it was just a coincidence that the TCAS was not triggered.
Well that is a briefing for military pilots and it is highlighting maintaining separation. Other ways to avoid triggering are not having very high climb rates or descent rates when there are aircraft above or below. So for example when overflying London and being descended in preparation for landing, I won’t typically do a 3000ft per minute descent when I know airliners are going to be vectored 1000ft below my cleared altitude. The TCAS should have been triggered in the subject flight obviously.
