Yes I was thinking the same it shows more messages just because you feed it sort of double to flightaware/piaware or something.
But also not sure 
I use it for tracking aircraft not using Mode-S. Although it doesnât identify the plane it displays the squawk / altitude of F15âs etc that come into range as a green trace.
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So what software youâre using?
I tried planeplotter but it is a sort of hell of a program so I stuck with the web interface of skyview and others.
At least in them I only see a increased message rate which is not send to the online services. only local and the also donât display in the web interfaces.
So not sure, maybe I;m totally wrong, Iâm not really an expert in linux. Just understand the basics
But hey, always willing to learn 
If anyone wants to make this their default, ssh into piaware, go to the web root, make a backup copy of the index and then edit it to add the parameter.
$ cd /var/www/html
$ sudo cp index.html index.html.original
$ sudo nano index.html
Scroll to near the end, add the #extended parameter where shown and save the file.
<div class="row">
<a id="map-link" href="/dump1090-fa/#extended" class="btn btn-primary btn-lg">Go to Map</a>
</div>
Now clicking the âGo to Mapâ button will always give you the extended Mode S data.
If you make a mess you can restore the backup copy and try again.
$ sudo cp index.html.original index.html
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Maybe someone can explain?
Transponder have different transmit modes.
The original one was called mode A.
Additional fields were added and then called mode C.
More fields were added and is then called mode S.
Then extended again and called extended mode S, aka ADS-B.
Then ADS-B was extended again and called extended ADS-B. (this was recently added to 3.6.2 version of piaware)
There are also more proposed extensions to extended ADS-B in the pipeline. Extended Extended ADS-B???
ADS-B has GPS lat and long positions in the messages. All the other message modes will need to be MLATed to have a plane position. The FlightAware system that does MLAT for mode S is different from mode A/C.
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Just to clarify some more⌠In rough order from oldest to newest technology:
Mode A responds to radar interrogation with a squawk code; Mode C responds with altitude; neither includes anything identifying the aircraft (no 24-bit address, etc) so itâs hard to do anything very useful with that data. PiAware does not upload or multilaterate A/C data. Skyview doesnât display A/C data at all. view1090-fa will display some basic A/C data (it tries to pair it up with Mode S targets where possible). A/C data is really only interesting to advanced users who have their own use for it; for everyone else, decoding it just uses extra CPU for no benefit.
Mode S provides 24-bit address, squawk, altitude, ident, and other transponder registers in response to interrogation; also ACAS/TCAS uses Mode S. Thereâs no position/velocity information in basic mode S. PiAware will multilaterate Mode S equipped aircraft that are not also ADS-B equipped.
Mode S EHS defines some additional transponder registers that provide additional aircraft data (roll, heading, airspeeds, autopilot settings) when interrogated for.
ADS-B v0 (DO-260) extends Mode S to transmit position/velocity/ident and some other data spontaneously, without radar interrogation.
ADS-B v1 (DO-260A) / v2 (DO-260B) add additional information to ADS-B transmissions including autopilot and squawk information. v3 (DO-260C), still in development, adds even more info.
The 3.6.2 âextended dataâ update decodes/displays Mode S EHS and the newer fields in ADS-B v1/v2.
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OR
to avoid a second instance of dump1090 as in view1090 running,
you can edit /usr/lib/piaware-support/generate-receiver-config
in receiver settings - here shown for type rtlsdr -
and add "--modeac". then reboot system and it will work.
ED1: you also need to put a line allow-modeac yes in /boot/piaware-config.txt for SD card images or in /etc/piaware.conf for the other systems.
also further down the same file added a remark (#) as shown
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Thanks for the info!
Thank you for the info you shared to us.
I did edit as per described and now modeac is ON even without typing view1090-fa --modeac in the terminal.
Great. Cheers~!
Regards.
You can also set âallow-modeac yesâ in piaware-config.
Given the posts by @david.baker & @Obj immediately above, what is the interest in decoding Mode A/C?
Probably no reason except because they canâŚ
useful for Planeplotter. seems to display aircraft ahead of Skyview. other than that ⌠because is available as a feature, and not all aircraft (very few, gliders, heli etc) are equipped with mode-s/ads-b.
Tried this but I do not get the modeac output to Planeplotter by this method.
do you have line allow-modeac yes in /boot/piaware-config.txt for SD card images or in /etc/piaware.conf for the other systems ?
Yes it is the default in the image
Should PiAware enable reception of Mode A/C messages when requested?
You may need to disable this if processing Mode A/C overloads your receiver.
allow-modeac yes
what is the receiver type set in PP. I use RTL > Rpi+Dump1090.
and under Optiosnsâ>Mode-S ReceiverâŚ
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Same settings and when using view1090-fa --modeac it works
there is one more change needed. i updated my original post, to alleviate the need of running view1090.
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How so?
If Mode A/C contains no position or identification, I fail to see how it can contribute to a quicker âfixâ.
Gliders typically use a completely different protocol (FLARM) that transmits on 868MHz.
While some FLARM receivers can decode ADS-B/C/S, do gliders actually transmit ADS-x?