Lack of transponder use - Midlands?

[RobertPBham]

Hi all,

This is just a general query for any one flying Midlands based (Wellesbourne) etc!

Has any one noticed a lack of transponder use in the general area by planes?

The reason I'm asking is that there have been a few occasions recently that I've spotted planes visually but had absolutely no Mode C/S pickup. They definitely haven't been transmitting ADSB/PAW.

I'm just trying to work out if something is wrong/not working on my PAW or people just aren't using their transponder.

I've also had an interesting occurrence on the ground - PAW located on dash in PA28 and Mode S detected from plane behind taxing past me but as soon as they've passed I've had no Mode S detection.

On the dash, the ADSB aerial is at a slight angle as it hits the windscreen - could this be a potential issue? If this was an issue, detecting a plane behind doesn't make sense.

Could the propellor/engine be shielding the signal?

Can the WIFI power interfere with the ADSB signal detection - I think I've turned mine up quite high?

Appreciate the help as it's difficult to test not knowing if other aircraft are transmitting data! :-)

Thanks
Rob

[RobertPBham]

This is a picture of the case setup which I place on the passenger side dash - in case this is causing any issues.

[Ian Melville]

That case should be OK, but not optimal. You will have some blind spots, but so will most installations. I also use a similar dash mounted PAW but use an all-in-one case.

Yup there are loads put there who don't have any transponder fitted (or any other electronic conspicuarity) , or fail to furn it to 'Alt'.

[exfirepro]

I've also had an interesting occurrence on the ground - PAW located on dash in PA28 and Mode S detected from plane behind taxing past me but as soon as they've passed I've had no Mode S detection.

On the dash, the ADSB aerial is at a slight angle as it hits the windscreen - could this be a potential issue? If this was an issue, detecting a plane behind doesn't make sense.

Could the propellor/engine be shielding the signal?

Can the WIFI power interfere with the ADSB signal detection - I think I've turned mine up quite high?

Appreciate the help as it's difficult to test not knowing if other aircraft are transmitting data! :-)

Thanks
Rob

Hi Rob,

Just to supplement Ian's reply -

Re the Mode S on the ground, the other aircraft's transponder will only transmit in response to a Radar or TCAS interrogation. On the ground away from major airports with Ground Radar, this can be very 'hit or miss' and would easily explain your anomaly.

Yes, Radio signals can easily be blocked by metalwork or other 'dense' objects (such as pilots / passengers, effectively large bags of fluid), but in the case of your PA28, other than a permanent antenna fit, yours should work fine in the air, as long as you are aware that there will be some blanking to the rear and below to the front. In most cases, you should get early warning as aircraft approach before they get into these 'blind spots'.

If you fly out of/into Wellesbourne, ask for Keith Vinning. He flies from there and I'm sure he would be happy to take a look at your setup/settings for you.

Regards

Peter

[Admin]

Seems like Ian and Peter beat me to a response 

So to back up a few of the statements.

Mode C/S transmissions are not automatic, they are only transmitted upon request, this means either from interrogation by Ground Radar, or a TCAS system. its unlikely to see an interrogation on the ground, the other aircraft may have been interrogated by a TCAS, or hit the 'ident' button, which I think forces a response.

Also regarding Mode C/S,  remember that all reception does not necessarily generate a warning.
If you want to see what PilotAware is receiving in terms of Mode C/S, take a look at the traffic page.
These signatures are only forwarded to the navigation device, based upon certain criteria
- relative altitude
- sensitivity

If you are not seeing Mode C/S listed in the traffic page - there may well be a fault, but I think this is unlikely

The acid test is to take a look at the traffic page, and determine whether it is showing reasonable information

thx
Lee

[RobertPBham]

Thanks for all the replies - very helpful!

I didn't realise that Mode S requires being queried by radar/TCAS - thinking about it now, I'm sure I knew, but had forgotten - hence the lack of returns! I'll do a thorough test via the traffic page when I'm a passenger/co pilot - I'm sure all will be working fine.

I also suspect a lack of transponders being turned on is the other cause! :-)

Thanks
Rob

[grahambaker]

Don't forget that there are still a lot a transponder equipped aircraft without an altitude encoder, so they only emit Mode A which is invisible to PAW.

[Admin]

Don't forget that there are still a lot a transponder equipped aircraft without an altitude encoder, so they only emit Mode A which is invisible to PAW.

Interestingly, not invisible, just dont know what to do with the data 

[grahambaker]

alright then... invisible to the user of PAW 

[tnowak]

I thought mode S would also transmit occasionally (every 5 seconds?) irrespective of whether being interrogated?
Isn't that how Mode S ADS-B out data gets "broadcast"?
Regards

Tony

[Moffrestorer]

Only if the Mode S Transponder is ES (ADS-B Out) capable and enabled by connecting it to a GPS source. Otherwise, for the basic Mode S it needs to be interrogated by a Ground Radar, as previously stated.

Chris

[Moffrestorer]

As of yesterday, 12 October, the final stage of SERA implementation came into force. One of the provisions concerns mandatory use of Transponders. In general, if you have a serviceable Transponder it is now compulsory to have it switched On and to ALT setting (to give Mode C output) during flight. Exceptions are if ATC request you stop squawking or if you are part of a formation flight in which case the leader solely does the squawk, until such time as the flight ceases to be in formation.

There is also a  provision concerning lack of an electrical system and Transponder functioning on limited battery power, but not sure what this says.

So no excuse not to be using Transponder, if you have one, as it's now required by law!

Regards,

Chris

[Paul_Sengupta]

Interestingly, not invisible, just dont know what to do with the data 

Would there be any way of adding this to the bearingless report in some way? Can you tell if a single transmission is Mode A only?

[Wadoadi]

Only if the Mode S Transponder is ES (ADS-B Out) capable and enabled by connecting it to a GPS source. Otherwise, for the basic Mode S it needs to be interrogated by a Ground Radar, as previously stated.

Chris

Chris, I think this may be wrong even without a GPS Mode S will send out SS unsolicited from the ICAO ref doc below:
Mode S SS (Mode S short squitter) Periodic unsolicited output of a Mode S transponder (nominally once per second) in a specific format to facilitate passive acquisition.

Mode S ES (Mode S extended squitter): Periodic unsolicited output Mode S signal format containing 56 bits of additional information.

[Moffrestorer]

Hi Wadoadi

I stand corrected. My own Becker Mode S is apparently ES capable yet cannot be connected to a GPS source without a hardware and software upgrade. I supposed, incorrectly, that the ES hardware was missing in its entirety yet close reading of the manual reveals that there is an acquisition Squitter (the short Squitter you refer to, 4/sec) and an extended Squitter (56 bit, once/sec). Just what these do, in the absence of ADS-B out, is anyone's guess?

Regards,

Chris