COAA PlanePlotter Review Part 3

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USAF JUVAT80 (Gulfstream V, 01-0076) - a successful Mlat!
USAF JUVAT80 (Gulfstream V, 01-0076) – a successful Mlat!


Assuming you have a fully operational set-up (GS/MU or just MU), you can now manually “Mlat” non ADS-B aircraft. For the most part these will be military assets, though it will become apparent that there are a fair few civil types that don’t transmit positional data too.

PlanePlotter Multilateration Tutorial PDF – How Mlat works

Unless you have read the Help Topics within PlanePlotter or the PDF file above it may not be that obvious what to do now and how Mlat works. Simply put – if a precise distance from an unknown location (position-less aircraft) can be received by 3 known locations (Ground Stations) it is just a matter of using geometry to determine the position of the unknown aircraft. Of course it is way more complicated than this simplified explanation and I recommend reading the PDF file above for a more thorough briefing.

To use the PP Mlat feature go to View… Aircraft list as position-less aircraft obviously do not appear in the chart view until successfully plotted. It is useful to mark additional sub search parameters from the Aircraft list display options notably: Aircraft without positions (shortcut key U) or Aircraft with Mlat possible (shortcut key M) as this will eliminate aircraft that have positions and make it easier to see what is or not plotted.

It is advisable to select a green coloured aircraft for Mlat. Check the altitude too as high flyers are more likely to be sharing raw reports across a broader sweep and thus picked up by numerous ground stations simultaneously.

There are two ways to Mlat: Ctrl+left click or Shift+left click. The latter initiates a series of requests. The title bar at the bottom of the screen will display the status of the Mlat request. A small pop-up progress window will also show the current request actions which include the total raw reports (messages) number of ground stations, amount of hyper curves, curve users and the hex code for the aircraft in question.

Mlat repeat request progress window
Mlat repeat request progress window

A sign that the request maybe successful is the amount of raw reports that are being received. If this rapidly increases during the process it is likely to result in an accurate and therefore successful plot. A minimum of 3 ground stations are also required and more will improve chances.

352 SOG MC-130's JOSH 34/35 Mlat over the Netherlands. Note the blue crossed circles, these are Ground Stations that are providing raw data for the Mlat
352 SOG MC-130’s JOSH 34/35 Mlat over the Netherlands. Note the blue crossed circles, these are Ground Stations that are providing raw data for the Mlat

If successful the display will change to Chart view and the aircraft will be displayed circled by a blue ring (default colour which can be changed) covered in curves (hyperboloids) and the location of the ground stations used to Mlat. The sequence takes 10 seconds and a countdown timer indicates progress through 2 cycles.

If unsuccessful the following message will be displayed:

  • No recent data for selected aircraft
  • Insufficient raw data sharers
  • Sharing state incompatible with Mlat request

Sometimes you just can’t Mlat a position-less aircraft due to low altitude, no data or insufficient sharers. Try another aircraft and hope for better luck!

I manually Mlat'd JOSH31-33 as they crossed the North Sea inbound Mildenhall. As they were directly overhead my location I nipped outside with a camera and...
I manually Mlat’d JOSH31-33 as they crossed the North Sea inbound Mildenhall. As they were directly overhead my location I nipped outside with a camera and…
... snapped this photo of one of the MC-130's at around FL100
… snapped this photo of one of the MC-130’s at around FL100

A very useful feature is the repeat request in Chart view. By using Shift+Ctrl+left click you can select an aircraft that is expiring (orange) and update its position if sufficient ground stations and raw reports are available. This sequence continues until either the aircraft is no longer plotting (i.e. landed, out of range or lacking sufficient data) or user cancelled by pressing the Esc (Escape) key after the pop-up progress window has closed or there is a red cross in the pop-up window itself. Selecting a new aircraft to Mlat or left clicking an aircraft in Aircraft view will also cancel the current request.

The Auto Mlat feature (Options… I/O settings) if checked will, whenever Plane Plotter is idle, try to Mlat any position less aircraft in the list that have sufficient ground stations in the sharer list. Unlike manual Mlat requests, information is displayed in the status bar and not in the pop up window.

Alert list
Alert list


Alerts can be set-up either via a conditional expression or the chart options (blue spanner symbol). This is the simplest method for inputting some quick alerts such as aircraft types or ICAO hex codes. I currently have the emergency Squawk codes (7500, 7600 and 7700) in my alert list and have alerts logged for daily review. If you have set-up an alert zone check the aircraft in zone box so that each aircraft that transits the zone gets recorded and alerted. SMS alerts are also available however you’ll need to prepay for this service before activating it. The alerts system is excellent, though I must say the whooshing jet alert sound gets a bit annoying after a while! This can be changed via Windows sound options or simply turned off (by volume).

Conditional Expression menu (click for full size image)
Conditional Expression menu (click for full size image)

Conditional Expressions (Condex)

Conditional expressions are the ultimate way to filter aircraft movements and display the results in various ways. We discussed their implementation in Part 2 and the same formatting applies. The set-up screen can be found under Options… Conditional expressions. There are 6 different options, but the most used will probably be chart/outline, though the alert expression can be very handy too.

Once clicked it all becomes obvious (well, sort of). A degree of experimentation is required to get desired results and the expressions need to be carefully thought out. At times it can be a challenge, especially when working with highly complex strings which fail to work! Double check every character – often its just a missing double quote symbol. Once you get the hang of how the condex works its very rewarding and a hugely powerful filtering system unsurpassed by any other plotting program.

Personally, I’d keep it simple – something like segregating aircraft types – particularly useful if you want to display just military fast jets for example. Make sure it works, then move on to something more complex such as being alerted when a specific aircraft type is within visual range of your location.

Here is an example I use to catch CV-22 Osprey’s out of RAF Mildenhall:

range < 10 & altitude < 5000 and type code = “V22”

In other words when an CV-22 is within 10 miles of my location and under 5000ft altitude (they don’t generally fly higher around here) the alert expression will notify me so that I can get outside and watch it fly overhead.

I really recommend checking out the conditional expression resources listed below. These sites contain some excellent examples and ideas for your own expressions.

Remember to check the enable this conditional expression or nothing will happen!

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