Primarily for general aviation discussion, but other aviation topics are also welcome.
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By Cub
FLYER Club Member  FLYER Club Member
#1846060
lobstaboy wrote:
Cub wrote:
Crash one wrote:So SE2 performance is compromised in favour of a compact unit, onboard battery, no sticky out bits.
Or is that stating the bleeding obvious?


I don’t believe the performance is compromised at all. The performance is based upon a requirement for short range air/air detection and conspicuity in accordance with a technical specification detailed in CAP 1391. The product achieves this. Surely it would only be ‘compromised’ if it didn’t achieve the requirement?


That is what you said @Cub in response to @Crash one saying the performance of SE2 is a compromise to allow it to fit in a small box with internal power.
"The performance is based on a requirement... ...in CAP1391". But there is no performance requirement in CAP1391 - lots of other technical requirements, yes.
So clearly you agree that it is perfectly possible for PAW to do what it does better than SE2, in a performance sense.

I am not critical of SE2 at all. It meets a requirement for EC and is very convenient. It's designers have done a good job. But they chose to make different compromises to the designers of PAW.
And, as pointed out before, we have no test data on either in terms of their performance. I totally discount the vector diagrams and the anecdotal review of the Flyer article - they just aren't technically sound.


I think you are comparing apples and pears. I am talking about the performance of an EC device designed to achieve short range air/air electronic conspicuity and detection, built in accordance with a technical specification published by an aviation regulator. PAW clearly may do other things better or worse against another set of requirements but most definitely is not compliant with CAP 1391. Clearly two very different products.

I think most GA pilots reading the pros and cons of each device will come to the correct choice for their situation despite no clear reiteration of policy or guidance from the CAA. My personal hope remains that people prioritise making themselves electronically conspicuous via ADS-B Out and then assess their further requirements and the merits of the various devices available.
By riverrock
FLYER Club Member  FLYER Club Member
#1846064
So a CAP1391 device could only broadcast in a bubble a few meters around the aircraft (so as good as a chocolate teapot) as there aren't performance specs?

What is the broadcast range of an SE2 and what effect does placing it in different orientations / against certain items (there was a photo going around of someone who had velcroed it neatly underneath the glare shield against the panel) make to that broadcast range?

Vector diagrams show where it has been detected using an enhanced antenna / receiver on the ground, but doesn't necessarily tell you which directions it isn't broadcasting, and what distance another receiver (such as another SE2 which doesn't have a large antenna) will see it broadcasting.
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By lobstaboy
#1846065
Dave W wrote:Point of Order: CAP1391 isn't a full technical specification.

It identifies capability, but includes no installed performance specs.


Precisely my point.

SE2 could be so duff that it won't see anything further than a hundred yards away, yet it would still be a CAP1391 device. I'm not saying it is, mind. I'm saying we have no data either way.
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By lobstaboy
#1846067
riverrock wrote:So a CAP1391 device could only broadcast in a bubble a few meters around the aircraft (so as good as a chocolate teapot) as there aren't performance specs?

What is the broadcast range of an SE2 and what effect does placing it in different orientations / against certain items (there was a photo going around of someone who had velcroed it neatly underneath the glare shield against the panel) make to that broadcast range?

Vector diagrams show where it has been detected using an enhanced antenna / receiver on the ground, but doesn't necessarily tell you which directions it isn't broadcasting, and what distance another receiver (such as another SE2 which doesn't have a large antenna) will see it broadcasting.


Yes!
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By leemoore1966
#1846074
To be fair to @Cub, he is absolutely correct, this is what is said in CAP1391
AMC 1391-4.4: ADS-B out requirements Due to the reduced transmitter power of EC devices covered by this requirement, it is accepted that the minimum air-to-air range specified in ICAO Annex 10, 5.1.1.3 for extended squitter transmitting and receiving systems in the classes specified, may not be supported.

This is quite a strange (non) requirement, but from Annex 10, the lowest specified A0 Device must have a minimum performance of 10nm for both transmit and receive.

In which case, the CAP1391 specification is saying that a CAP1391 device does not have to meet the minimum performance of the (lowest performing) A0 device

More importantly, it does not specify what it should meet, so Cub is perfectly correct, the performance range in any direction for a CAP1391, is completely unspecified
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By lobstaboy
#1846086
leemoore1966 wrote:...so Cub is perfectly correct, the performance range in any direction for a CAP1391, is completely unspecified


Well I rather feel that Cub was being ambiguous and that it took me and DaveW to point that out - but at least we all agree!
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By Cub
FLYER Club Member  FLYER Club Member
#1846091
lobstaboy wrote:
leemoore1966 wrote:...so Cub is perfectly correct, the performance range in any direction for a CAP1391, is completely unspecified


Well I rather feel that Cub was being ambiguous and that it took me and DaveW to point that out - but at least we all agree!


I don’t agree with you. I don’t feel I have been ambiguous at all.

I contest that the performance of a properly positioned and orientated SkyEcho is perfectly acceptable as a short range ADS-B conspicuity and detection device.

I additionally confirm that I believe that the device is built in conformance with the requirements of CAP 1391 which, as Lee points out, contains no minimum range requirement, which is hardly surprising for a carry-on device, with no external antennas, which is subject to the vagaries of how the pilot chooses to position it on the airframe.
By riverrock
FLYER Club Member  FLYER Club Member
#1846093
@Cub - can you define "perfectly acceptable"? A 10 n. mile range? Less? Will there always be blanked areas (such as where engine is in line)? Is that acceptable?

Can you agree that SE2 shouldn't ever be thought suitable for ground detection / access to airspace as its range may not reach a central ground station?

I guess its just ensuring that each system meets a pilot's expectations, and the limitations are known and understood.
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By Wide-Body
FLYER Club Member  FLYER Club Member
#1846098
Cub wrote:
I contest that the performance of a properly positioned and orientated SkyEcho is perfectly acceptable as a short range ADS-B conspicuity and detection device.



It is not "Perfectly" acceptable. Both devices are away from perfect.

They are however acceptable in the reduction of MAC risk, and their compliance with the current legislation (however flawed).

My opinion is based as an end user of both systems.
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By ls8pilot
#1846101
riverrock wrote:[usermention=2700]
....
Can you agree that SE2 shouldn't ever be thought suitable for ground detection / access to airspace as its range may not reach a central ground station?

I guess its just ensuring that each system meets a pilot's expectations, and the limitations are known and understood.


I respectfully would'nt agree with the blanket statement above - for ATZ use a 5nm radius round the tower should meet the need & there are plenty of SE2 installations that meet or exceed that. It may be that for some aircraft an internal antenna is not a suitable solution, but there are plenty of aircraft for which it works fine, we should maybe avoid generalisations that will discourage people from fitting EC devices which will work adequately in their situation

Meanwhile of course if someone would like to set up a company, design & certify a device to CAP1391 standards which has a better and/or external antenna then I'm sure they will sell like hotcakes ?

Unfortunately I think it unlikely that Flarm or P3i will be thought "suitable for ground detection access to airspace" either.....

(PS it's anecdotal and not representative, but my SE2 has been detected at over 30nm air to air - by a PowerFlarm receiver)
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By Cub
FLYER Club Member  FLYER Club Member
#1846104
riverrock wrote:@Cub - can you define "perfectly acceptable"? A 10 n. mile range? Less? Will there always be blanked areas (such as where engine is in line)? Is that acceptable?

Can you agree that SE2 shouldn't ever be thought suitable for ground detection / access to airspace as its range may not reach a central ground station?

I guess its just ensuring that each system meets a pilot's expectations, and the limitations are known and understood.


It is perfectly acceptable to me which is really all that matters, these days. I think there is plenty of evidence from the Flight Information Display (FID) trials that a CAP 1391 device is also acceptable for the ground based, short range detection required to enhance the traffic information provision by a suitably qualified FISO or A/G operator.
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By lobstaboy
#1846120
Cub wrote:
I contest that the performance of a properly positioned and orientated SkyEcho is perfectly acceptable as a short range ADS-B conspicuity and detection device.

I additionally confirm that I believe that the device is built in conformance with the requirements of CAP 1391 ...


I'm happy to accept these points, Cub, as long as we don't have to define what we mean by 'short range'.
My argument stems from your assertion that SE2 does not represent a compromise in terms of performance. I and others maintain that it does. Whether that matters or not I have no idea since we have no reliable performance data..
I'll say again - SE2 designers have done a good job around the compromises that were necessary for them to work within. Maybe another company would come up with a different CAP1391 solution - say with an external antenna?
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By ls8pilot
#1846129
I wouldn't disagree @lobstaboy , but to be fair my impression is that a substantial percentage of PAW users rely on internal antenna and I've not seen much systematic analysis of how that performs either.

I wonder what is an acceptable air:air warning? With Flarm:Flarm it can quite short head:head, maybe 10-15 seconds (closing speed for two gliders head on typically 120 to 180kt) At, say, 240kt closing speed 4nm range gives you a minute to react, so if SE2 is better than that it should bring benefits.

Unlike TCAS an EC system is meant to augment visual acquisition, so I'm not sure how useful it really is knowing about traffic 10nm plus away?
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By Tim Dawson
SkyDemon developer
#1846133
lobstaboy wrote:I'm saying we have no data either way.


It isn’t true to say there’s no data available.

Ian did a good review of SE2 and PAw using multiple devices and aircraft, and that contains lots of information on the air-to-air ranges observed, if I recall correctly.
Last edited by Tim Dawson on Mon May 10, 2021 6:13 pm, edited 1 time in total.
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