ACARS FAQs Note on sharing

There are four main ACARS frequencies for the UK and Europe.  These are 131.525, 131.725, 131.825, and 136.750 MHz.  The mode is AM, so use the line, headphone or speaker output, and not from a discriminator tap!.  Traffic appears to be evenly shared between all four frequencies, so if you have the facility to scan them all, then do so.

ACARS FAQs

• Q: Although my ACARS message log is big, I am not seeing many plots on my screen.
• A: The ratio of ACARS messages which contain position reports, to those which don't, is very small.  Don't expect to see a screen full of red triangles within five minutes of running your system. The keyword with ACARS is PATIENCE!

• Q: Sometimes I can see a string of red triangles spread out across the world.  How can this be, given that (a) VHF ACARS is 'line-of-sight', I am in the UK and some of these plots are in India, and (b) the aircraft can't possibly be in all those positions at the same time, can it?.
• A: PlanePlotter searches through the body of ACARS messages and extracts positions which it recognizes as having a valid Lat and Long format.  In the case of messages which contain more than one valid position,  PlanePlotter obviously cannot tell which position is the current one, so it plots them all.  The most well-known examples are the VHF ACARS Oceanic Clearance messages from Shanwick, which normally contain positions in full (e.g 50N 20W, 50N 30W, 50N 40W etc).  If you DON'T want to see a string of red triangles cluttering up your map of the North Atlantic, or wherever, then click on Options...Acars decoder, and then tick the 'override reports' box.  That way, PP will only display the latest position and will update it whenever a newer one is found for that particular flight

• Q: Why do some British Airways flights appear over the Gulf of Guinea when they're actually over the North Sea?

• A: The A319s and A320s in the G-EU.. range appear to be fitted with ACARS units which insert a leading zero into the "Degrees of Latitude" column. Seeing as how latitude can never be more than 90 degrees North or South, one wonders what the thinking was behing this.

  Be that as it may, it means that a true latitude of, let's say 50.164N becomes 050.164N in the ACARS message and is interpreted by PP as being 5.0164N. I believe this is something to do with the way PP looks for, sees and reads the position format; I may be wrong. The result is that the position is in error by about 50 degrees of latitude, which will effectively plot the flight as being somewhere off the coast of Ghana when it's really over Clacton, UK.

• Q: I can sometimes see blue, magenta, and green triangles on my screen.  What do they mean?
• A: See: "what do the different colours mean", on the Customising the display page.

• Q: When I look at my message screen I can often see corrupt messages, and there's sometimes a squiggly line [~] at the start of the message. What does that mean?

• A: It could mean that you are overdriving the audio input, or (more likely) you have not checked the "CRC correct" box, and Planeplotter is thus displaying both corrupt and error-free messages. For details regarding the significance of the "CRC Correct" option, see HELP....Help Topics...Options...Display....Decoder Options....display. If you only want to see error-free messages (and maybe cut down the size of your ACARS log at the same time) then you'd be well advised to click the "CRC Correct" box  (OPTIONS....ACARS Decoder)
• Note also the following advice from Bev, issued with the release of PP Version 5.4.1 (2nd Aug 2009)
• (quote) PP is now more assertive about not sharing ACARS reports if the Options..Decoder..CRC condition is not set. Previously, there were circumstances in which corrupt ACARS messages could slip

  into the sharing system (unquote).

• Q:  When I stop processing, clear the screen (Options...Purge....Purge flights) and select REPLAY Yesterday's ACARS log, (Review....Yesterday....Replay yesterday's ACARS log) my screen does not show any aircraft.

   

• A:  In order to display yesterday's plotted aircraft, your "Omit aircraft after" time must be set to at least 24 (hrs) x 60 (mins) , i.e 1440 mins. In reality, set it to some hideously ridiculous time like 5000 mins; that should work. Don't forget to Purge the screen, reset the "Omit time after" to its previous value and then click on the green 'Start Processing' button afterwards, otherwise PP will just sit there and stare at you, while you sit there and stare at IT!

• Q: Is it possible to see just ACARS traffic on my screen, and exclude SBS/RB traffic? I'd like to see other sharers' ACARS plots, nothing else.

• (A) Yes it is possible
• (1) Click on Options...chart...options

• (2) On the pop-up window, in the 'Plot Aircraft' section, untick every flight level EXCEPT the one marked FL325-335.

• (3) Clicking on the FL325-335 button will open another window which allows you to set the upper and lower limits of the Flight Level interval.

• (4) As ACARS position-reporting aircraft cruise at at a fictitious height of 33333 feet, delete the default figures of 325 and 335 and replace them with 332 as the lower limit and 334 as the upper limit. You will also see that the neighbouring flight level boxes will change to reflect this alteration.

• (5) Click OK on the flight-level limit window, then click OK to close the 'Options' window.
• (6) Note that with this setting, you will see SBS and RB traffic as it passes through FL333 on its ascent or descent, but such traffic should be short-lived.

Don't forget: If the previous settings were saved as a configuration, you will need to save the new settings otherwise all your hard work will have been in vain.

Note on sharing

If you are sharing your ACARS traffic, the only reports which other people should see should be the flight's current position (a red triangle).  Predicted positions over significant UK waypoints appear as magenta triangles.  These are NOT sent via the COAA sharer, so no-one else sees them.

[Text supplied by Dick Ware - many thanks]