Mode S Miscodes

[Hawkeye]

I had two Mode S codes and therefore two registrations for the same flight in MyLog yesterday as shown in the attachment.

Any body know how and why this comes about?

It’s pretty obvious when two entries appear one after the other as these two, that one of the Mode S codes must be wrong, -  it’s actually 400C47 that’s the wrong ‘un, having checked one of the Glasgow Movements sites – but I wonder just how often single entry miscodes, which wouldn’t be picked up, occur and therefore how sure RB users who bought the unit to log the aircraft seen from their homes can be of the aircraft’s true identity

Regards

Syd

[ACW367]

It is a corruption bug that has been extensively reported to Airnav before.  The software gets confused with two hexcodes with closely related 24 bit addresses.

If you go to your mylog you will find entries like this.

400B04  BEE7RV                   G-JEDW  DH8D  FlyBe                2011/02/25 15:38:04 
   400B04  SHT2P                    G-JEDW  DH8D  FlyBe                2011/02/25 15:41:28 
   400B00  SHT2P    EGLL-EGCC       G-EUXH  A321  British Airways      2011/02/25 15:39:08

It was last reported here. 
http://www.airnavsystems.com/forum/index.php?topic=5940.msg62192#msg62192

Airnav's response that "Nothing can be done regarding this." is here:
http://www.airnavsystems.com/forum/index.php?topic=5940.msg62194#msg62194

I am currently drawing together all the reporting of this that has occured on the forum over the years, alongside my own recent notings of this bug occuring.  This is to provide airnav the full detailed analysis of the bug.  As they requested on those threads.  If you wish to do your own analysis in parallel you could always PM them to Airnav Development.  They are interested in recieveing instances and analysis of all reported bugs at the moment, to increase their understanding of how the many ongoing issues affect the system, as they are now looking to develop fixes. 

[ACW367]

it’s actually 400C47 that’s the wrong ‘un, having checked one of the Glasgow Movements sites – but I wonder just how often single entry miscodes, which wouldn’t be picked up, occur and therefore how sure RB users who bought the unit to log the aircraft seen from their homes can be of the aircraft’s true identity

Regards

Syd

Forgot to answer the latter part.  In high density areas like the UK on recieving 1000 movements it can be up to ten instances when this corruption will occur IE around 1% and when it occurs you cannot guarantee that the aircraft showing on your screen is indeed the correct one or is the spurious one that is actually somewhere else in your radio range.

I once physically watched an easyjet A319 fly low over my head into Luton showing on my box as a BA Shuttle flight with G-EUU* registration.  Whilst the easyjet callsign and G-EZ** registration was attached to a track climbing out of heathrow.  After about 5 mins the tags swapped over back to the correct airframes.

[AirNav Support]

The specifics of this issue are hard to rectify as this issue as such would affect all receivers. In busy areas you could be getting beyond 500 messages per second and therefore you do have chance a good chance of corruption of a signal.

When there is a difference of a one letter of the mode-s code, all we can do is say we have one message received but we will wait till lets say we get 2 of the same mode-s to reduce the chance it was a one off corrupted signal. However doing that you may loose that one message you might have got from an aircraft which just skirted your reception area.

This is industry wide issue and many people in the industry have said you should have multiple receivers in busy areas monitoring small areas rather than one receiver monitoring the whole area to combat these issues.

We all want 250nm range but in doing so we are open to these types of issues arising.

[ACW367]

Thank you for a very full and frank explaination Airnav.

[Hawkeye]

Thanks to both of you.

Re AirNav's second paragraph, personally I'd rather miss the one on the periphery of my reception area 'cos I'm more interested in WYSIWYG. Id make a guess most users are.

regards,

Syd

[eggplant]

Just an idea - how about making it a user preference setting ??

[phil zech]

All,

This Mode S problem seems to be getting worse, I never really noticed it before but today in My Flights  it seems to happening virtually all the time with at least 1 aircraft having its  flight details allocated to a Mode S number, 1 digit different , letter or number.

Example:  400B04  BEE4MP  G-JEDW  DH8D  Flybe

                400B06  BEE4MP  G-GOTH  PA28

Im no expert, but I do not understand how a totally different number can be confused with a different code. Isnt that the point of the codes.

Please can this fault be looked and  rectified ASAP.

Regards


Phil

[chewycanes]

Hi Phil

I also have had this happen a number of times and i do have alot of traffic being received.

My question is :-

I can undersatnd a code being detected and is a corruption of another aircraft currently being detected. But why does it continue to be detected as long as the real aircraft is still being detected ?

Surely if the proper code is being received then the corrupted code should no longer be seen and timeout. I have seen the wrong code timeout and then return along side the proper code.

Airnav i think it still needs some checking.

Brian

[AirNav Support]

Phil,

Take a look at our response earlier on in the thread, this affects all recievers and its different of one letter/number that can be corrupted than can cause problems.

Brian,

How does the RadarBox know which is correct and which isn't? Not a simple as it looks when we see it on the screen can work it out.

[chewycanes]

Hi Airnav
Thanks for your quick response.
I understand the box does not know which is correct.

I want to to just get this right in my mind so bare with me.

Scenario
RB Receives wrong code 400B00 and is displayed.
RB Receive correct code 400B02 and is displayed.

Both aircraft are now being displayed.

Now for these to be displayed then the following must apply :-

a) both signals must be being recieved by the RB or
b) one signal continually corrupted giving both codes.

Which do you think is happening?

Thanks
Brian

[tarbat]

Now for these to be displayed then the following must apply :-

a) both signals must be being recieved by the RB or
b) one signal continually corrupted giving both codes.

or:
c) Your timeout settings allow both to continue to be displayed.

I'm not saying that's the cause in this case, but it's worth checking that your local timeout settings are sensibly low to ensure that where a corrupted code is received it timeouts promptly.

Also take a look at the Message Count for the latest flight of the corrupted code.  That will tell you how many corrupted messages RB recieved.

[AirNav Support]

In most cases both signals are being received.

Remember from one aircraft you could be getting a few replies with there Mode-S details every second. Therefore if your timeout is set for 30 second it just needs just 1 message out of 90 mode-s messages in that 30 second period to be corrupted for the corrupted to keep appearing by the correct ones side.

[chewycanes]

Tarbat & Airnav

Thanks for your quick replies.

I understand now what you are saying.

Thanks

Brian

[phil zech]

Thanks for all replies on this subject

What do people regard as a "sensibly low" time-out figure to hopefully ensure these "rogue" aircraft are removed ASAP from My Flights ?


Just one more question on this are these rogue aircraft  in flight when they are wrongly credited with another aircrafts flight number.

Im still slightly confused by this because I have had a RB for 2.5 years, and have only noticed this problem in the past few weeks, I would have noticed before as on average I only have 35-40 in My Flights at any one time and duplicate Flight numbers would be noticed.

Just out of curiosity to anyone who uses "another receiver" does this problem exist  as stated earlier.


Regards

Phil