Frequently Asked Questions

Here are some frequently asked questions about the tracking programs at this site and APRS in general.

• Did the airplane crash if it can no longer be found on this site?
• What should I do if the airplane is overdue?
• How does this technology work?
• What stations are tracked?
• For how long will position reports be available?
• How do I use Google Earth to "fly along" or play a tour of a track?
• How can I contact the site owner?

• Did the airplane crash if it can no longer be found on this site?


Probably not.

More likely is a failure in the APRS tracking chain of equipment.   You must remember that this is amateur radio, not "professional radio". The network of amateur radio ground stations as well as the aircraft APRS installations are run by individual radio amateurs and not tested or maintained to any specific standard.  Hardware, software, and human failures happen every day.

The most likely explanation for a "missing" airplane is some sort of system failure.  In approximate order of likelihood:


The aircraft is not in an area of radio coverage.  This happens when the airplane is too low to reach a ground station or is blocked by terrain or has a substandard antenna installation.


The server is (temporarily) down or the feed of position reports to it from the ground stations has been (temporarily) interrupted.


The pilot forgot to turn on his APRS tracking equipment or has turned it off (either on purpose or accidentally by bumping a switch). The equipment could have blown a fuse or sufferered any number of other malfunctions.

• What should I do if the airplane is overdue?


Be sure you have given the airplane enough time to reach its original or an alternate destination.   Consider the possibility of a change in plans and flight for considerably longer than initially planned due to weather diversion or another reason (within the limits of the fuel on board).

Then you can accomplish these steps in sequence:


First, attempt to contact the pilot at his destination by cellphone or other means.


Next, contact another party at the intended destination and inquire on the whereabouts of the aircraft.  Contact any friends or family members that may know the location of the aircraft.


Finally, when you have exhausted all means to locate the aircraft, contact the FAA to report an overdue aircraft.   Once way to contact the FAA is by telephoning the Automated Flight Service at (800) WX-BRIEF (800-992-7433).   Ask for a "briefer".   Be prepared to give specific information about the aircraft's last known position, the pilot, and the pilots intentions.   Flight Service will initiate the Overdue Aircraft procedure.

• How does this technology work?


A combination of radio and TCP/IP ("the Internet") communication is used.  The aircraft position and other parameters (as measured by an onboard GPS) are transmitted from the aircraft in real time to a network of amateur radio (ham) ground stations on VHF (the radio link).   Any ground station(s) receiving the transmission forward it to a network of servers and they in turn feed it to this site's server (the TCP/IP link).

At this site, the server filters and parses the TCP/IP feed and the resultant parameters are used to populate a database of position reports.   The database is queried and displayed by a number of scripts running on a web server.   This is all done by a combination of Perl, MySQL, Javascript, and HTML running on a dedicated PC in my hangar, using my home internet connection.

Other web sites (see the APRS Tracking Links on the sidebar at the left) also receive the same TCP/IP feed but populate and display their own databases.

The on-board equipment needed for tracking can cost from about $75 to over $200 and consists of the following:


GPS.  Often the aircraft GPS can be used.  Or a dedicated "puck-style" GPS device such as one from Argent Data Systems or Byonics can be used.


Transceiver.   An amateur radio transceiver capable of transmitting on 144.390 MHz at any power level (i.e. one watt is just fine).


Antenna,   An external vertically polarized antenna (such as a bent whip) is best but a "rubber dummy load" can give acceptable results.   A spare COM antenna is nearly ideal and even an unused VHF NAV (VOR) antenna will work fairly well.   Generally, a horizontally polarized antenna in a poor location (such as in a wingtip) will work somewhat but will give inferior results (reduced coverage at lower altitudes).


TNC or modem-like device (e.g. a "tracker") that converts the digital data from the GPS to audio tones transmitted by the transceiver.  One low cost device is the Byonics TinyTrak3+.


This device is an all-in-one turnkey solution ($150) although it does require a GPS connection.  

• What stations are tracked?


All airborne APRS stations in the USA and Canada transmitting either the small airplane or large airplane symbol are tracked.   "Aircraft" that appear to be ground vehicles ("fly" on roadways and at lower speeds) are filtered out.   Note that a very small number of non-aircraft mobile stations are also tracked as favors to individuals and there's an occasional balloon.

APRS stations not tracked here can most likely be found at one of the APRS Tracking Links on the sidebar at the left.   aprs.fi is recommended for ground-based stations.

In addition to APRS stations, certain ADS-B aircraft (generally within a 60 NM radius of Independence, OR) are also tracked on this site. These are generally small aircraft; scheduled airline ADS-B position reports are ignored. The ADS-B technology is entirely separate and different from APRS but ADS-B aircraft are displayed alongside APRS for no special reason other than that is my preference.

• For how long will position reports be available?


APRS position reports are generally retained for one year and ADS-B for two months in order to maintain reasonable database file size and performance. Certain position reports will be deleted in less time.   Here are some conditions under which position reports will be deleted before a full year has passed:


• If a station with an aircraft symbol is found to be a ground station (or mixed ground and air), all of that station's position reports are deleted and new ones will not be displayed.


• If position reports arrive via UI-View32, DSTAR, or other direct injection into the APRS IS servers (i.e. non-RF methods), those position reports are deleted.


• If a station beacons excessively (too frequently), that station's position reports are deleted much sooner than after one year.

• How do I use Google Earth to "fly along" or play a tour of a track?


Lets assume you're reading this because you'd like to try the Google Earth network link or track/tour functionality from the user interface page (items 8. or 9.) or the page that displays all tracks for a particular station.   Lets further assume that you have Google Earth installed on your PC and have at least a little bit of experience using it.

The Google Earth network link functionality is only useful if a station is presently in motion.  It displays a "birds-eye view" of what the pilot sees and is refreshed every 30 seconds.  If the aircraft has moved the station's icon "flys" to the new position and the map is refreshed.  No operator action is necessary to see a continually updating display. When the station stops moving, there are no further updates.

The Google Earth track/tour functionality displays a previously completed track or "replays" a track by "flying" a tour of it. It creates a collection of points in Google Earth's Places pane (under Temporary Places) that can be viewed or "toured".  Select Tools | Play Tour from the menu or use the controls below the Places pane to start, pause, or stop the tour.

Here are some tips for optimum use:


Do not check more than one network link or track simultaneously in the Places pane or Google Earth will attempt to fly back-and-forth between them.  This is probably not the effect you want.


You can save an interesting network link or track permanently under My Places and revisit it by checking it whenever you run Google Earth.  Again, check only one item at a time.


The default parameters are generally satisfactory for the Tour but they can be modified to taste by selecting Tools | Options | Touring tab from the menu.

• How can I contact the site owner?


Email is available under certain conditions explained here.  I (Joe Dubner) would appreciate any reports of error messages or unexplained operation so I can address them. (No one has ever done this.)

I cannot promise to implement enhancements regardless of their worth as I've moved on to other projects and barely maintain this site now but feel free to speak up.