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Evidence of transponders being turned off (and can primary radar see altitude?)

This report

In terms of failure to plan separation this one is nearly as bad as the RAF Grob Tutor mid-air.

It is very interesting that both pilots claimed to be operating a transponder but no secondary radar returns were observed. This would appear to support the hypothesis that pilots in the UK are flying without turning them on. I wonder if the AAIB commenting on this will make the CAA look a bit more closely at the unwanted effects of their airspace infringement policy.

It is odd that the report offers no information or comment on the altitude the aircraft were flying at, other than the perhaps obvious implication that they were operating mainly beneath the 2,500 base of the LTMA. The SkyDemon screenshot in the report suggests it occured at about 1,600-1,700ft. One presumes that in that location there is no chance they were too low for a secondary return to register on radar.

Last Edited by Graham at 10 Sep 17:14
EGLM & EGTN

One flying school I know of was looking to purchase an additional training aircraft and the seller sheepishly told them it only hand an old narco mode Alpha transponder.

They were then somewhat surprised when the buyer said “excellent that’s exactly what we are looking for”

Rather unsurprisingly they fail to mention that if you go through the re-education course once next stop is license suspension.

Off_Field wrote:

Rather unsurprisingly they fail to mention that if you go through the re-education course once next stop is license suspension.

I think the CAA comment was carefully positioned so as to give the impression that only prosecution counted as any sort of sanction.

It is entirely possible that the AAIB are detached enough from light GA to accept that CAA comment at face value.

EGLM & EGTN

Having just been on a 400 mile flight my impression (and it was only that) is there were more class A contacts than I have seen before on TA, but of course this gives no indication of totally non transponding aircraft at all.

I would have thought the CAA would have the data.

That said, I am never sure how good and how much primary radar cover there really is, and, to what extent primany can be used to ebable the CAA to take regulatory action?

They could at least try to measure the amount of non txp traffic comparing primary and secondary radar data.

LFPT, LFEH

This is prompted by another thread, but I realised that I have no idea how widespread primary radar is and just what are its capabilites? Inevitably primary provides the only mechanism for identifying and tracking non TPX traffic, but how effective is it? What are its tolerances?

If you watch the White Waltham area on FR24 you see very little activity. This does not correspond at all with actually happens there (lots of comings and goings, many obviously with Mode S). This is alluded to in the report, but it is not within the remit of the AAIB to dig any deeper.

As a member of West London Aero Club (the White Waltham operator) I receive fairly regular comms asking pilots to do what they can to prevent the Heathrow alarms going off. Last year they lowered the OHJ height from 1300 to 1200 for this reason. They’ve never asked us to do anything with our transponders, but the phrasing of the comms is clear enough to let you know that transponders (via CAIT) are the problem.

EGLM & EGTN

Primary radars are fairly ubiquitous – those big radomes or big latticework antenna reflectors are all primary; secondary radar antennas look like narrow horizontal beams.
There are about 160 civil primary radars in Europe plus some military ones. Maximum range is typically 100-250 NM for enroute radars or 30-60 NM for approach surveillance radars, and the resolution would be 1-2° in azimuth, about the same in elevation, and 0.1-0.3 NM in range. The main problem in use is the lack of reliable identification of aircraft. It also costs a lot to operate, and a significant part of that cost is electric power. Power consumption grows very steeply with maximum range, as the required radiated power increases as the fourth power of range, whereas for a secondary radar it’s only the square of range.

Last Edited by Ultranomad at 11 Sep 10:11
LKBU (near Prague), Czech Republic

Fuji_Abound wrote:

Inevitably primary provides the only mechanism for identifying and tracking non TPX traffic, but how effective is it? What are its tolerances?

You send an F16 to get you the ID, that is how it works “outside Europe”
Depending on the settings sometimes it may confuse a double deck bus or birds gaggles with a Cub but that is a different story…

Last Edited by Ibra at 11 Sep 10:36
ESSEX, United Kingdom
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