Comparison of 3 Flight Tracking Services

FlightAware, FindMeSpot, and APRS

by Dave Morris, 20 May 2008
Updated 8 December, 2008

The Flight Test
Below you see the AeroPlanner flight track for a trip I took on May 19th, 2008, from Dayton International (KDAY) in Dayton, Ohio, to Northwest Regional (52F) just north of Fort Worth, Texas. The dot near the center of the flight path is a lunch stop at Dexter, MO (KDXE), which has a nice little restaurant on-field right next to the fuel pumps (you must try it!). There is also an unscheduled stop at Mena, AR (KMEZ) because I had been fighting 50 mph headwinds and projected a lack of sufficient fuel to make it into my destination without making one more stop.

You will notice a bump in the lower half of the flight path, as I was advised to go around the Hog North MOA due to military activity, just before descending into Mena.

Next I will present 3 different options for tracking this one flight, and show you the variety of different levels of accuracy you can get from these 3 different methods .

This is the list of waypoints:
Option #1 - FlightAware.com
You may be familiar with www.FlightAware.com as a method of tracking airline flights and General Aviation flights on instrument flight plans. As I am writing this, they do sometimes include VFR flights on Flight Following, but as you can tell from the track to the left, those VFR tracks are not very accurate! But it does seem that more and more VFR flights are showing up in their database.

Despite using Clearance Delivery on the ground at Dayton to obtain a squawk code for Flight Following, they don't show me as originating from KDAY but rather from KOXD. And despite picking up Flight Following again for the KDXE-KMEZ leg as well as the KMEZ-52F legs, they never show any of those tracks at all!

Anyone using FlightAware to track my progress might deduce that I had never left Dexter.

This is really pretty useless information
Option #2 - Spot Messenger
There is a new device you can buy for around $150 now that acts as a sort of PLB (Personal Locator Beacon). You can order it at www.FindMeSpot.com, or occasionally deeply discounted elsewhere. A small, brightly colored box you can clip on the seatbelt, this tracker has an onboard GPS and a satellite phone transceiver. You don't talk into it, but rather use it to send 4 different types of messages: 1. I'm OK, 2. I need help, 3. MAYDAY (911), and 4. a tracking blip every 10 minutes.

Before you go anywhere, you log into your account on their web site and set up the people you want to receive the messages, whether text messages to a cell phone, or emails to an email address. Once set up, you just press the appropriate button on the Spot Messenger to send the message along with your GPS lat/long coordinates.

The regular service costs $100 a year to do the first 3 of those message types. For an additional $50 yearly subscription, you can also have the 10 minute tracking information sent.

However, I found it a little error-prone to use. Here's why: You use the same button to send the "I'm OK" message as you do to start up the 10 minute tracking blips. There is only one LED to tell you that you have initiated something, and if you don't do the button presses carefully, you will send just the single "I'm OK" message instead of starting up the 10 minute interval transmissions. And you can't really tell from the LED which you've done. So far, I have never gotten this right, and I'm always missing one or the other transmission. To their credit, the company has now installed an interactive tutorial "simulator" on their web site to hopefully help us memorize these important button sequences.

So, if you look at the FindMeSpot.com track below, you'll see I did not even have the 10 minute interval transmissions engaged until I realized the LED was not blinking at the correct rate, and pressed the button again somewhere around Evansville, Indiana.

They now also offer a "sharing" feature that will allow people to look at your track, either with or without a password, your choice. This is a nice change from the previous version that required you to give visitors full access to your entire account. They have now also fixed the 24 hour limit, so you can now view previous days' tracks. And they number the waypoints in chronological order now as well.

This system has the advantage of using satellites, not ground stations, for positioning and for communications. So it should work well even at low altitudes and in remote terrain. But coverage does not seem to be 100% with the device clipped to my shoulder harness in my Mooney next to the window. As you can see in the example on this page, there are only 14 waypoints. There should have been 54 waypoint logged. Obviously quite a number were lost, either due to GPS not being able to determine location, or due to the satellite phone not being able to reach a satellite to transmit the location.

I have noticed this on several other flights. There will typically be gaps. On a recent trip, it lost 11 out of 30 transmissions. (Oddly, or maybe just coincidentally, the major gap was in the same area both going and coming, between Lake Tawakoni and Lake O' The Pines, in East Texas. In one case I was at 5500 feet, in the other, 6500 feet.) So you should not rely on this device alone to give your position every 10 minutes in flight if your health and welfare are at stake.

Here is an excerpt from CarolAnn Garratt and Carol Foy's ALS Dash for the Cure (around the world in 7 days in a Mooney). Note the large gaps in coverage.

Also, here is an example of GPS inaccuracy. With the exception of number 16, the plane was sitting in exactly the same spot the entire time.

That having been said, I carry this with me all the time and turn on the tracking beacon on every flight. It's cheap insurance.

Option #3 - APRS
First of all, I'll just warn you that APRS requires a ham radio license, so it won't be for everyone. APRS is an Automatic Position Reporting System that is gaining in popularity among amateur radio operators. I was able to buy the Microtrak 8000, a small 8 watt tracking device, and a GPS from Byonics.com for less than $200 that runs on a 9V battery and requires no further subscriptions or periodic payments. I threw the Microtrak on top of a suitcase in the back seat of my Mooney, with the GPS near the North (right) window, and a quarter wavelength whip antenna lying horizontally across the suitcase. (Being inside a solid metal fuselage like that is NOT an ideal setup, but it does show what the system is capable of doing with a temporary setup!)

It does, however, rely on line-of-sight distance to a nearby ground-based ham operator for its operation. Each of the dots you see on the map below corresponds to a transmission from my device that was received by a ground station. So you will see in the map below that there are locations where many reporting points are logged, and other long stretches where there are no dots. The lines are drawn by the web-based program used to display the track, and are merely connecting the dots.

There are several mapping services that extract data from the APRS database and display it. A few of these are www.APRS.fi, www.APRSWorld.net, and www.FindU.com

I am a bit curious as to why there are no dots around Evansville. The only guess I can make is that I was in light rain for about 20 miles transitioning the Evansville area, and maybe that interfered with the transmissions. The other possibility is that the battery went dead. The next dots you see are near Dexter, and that's where I replaced the battery with a new one, just so I knew there would be a fresh battery for the second leg. I never bothered to see if the first battery had died. (By the way, a carbon 9V battery will not power this unit. It requires an alkaline battery.)

Look at the 3 dots in a straight line to the left of the word "Hot Springs" on the map below. What you can see clearly is that, once I dropped below a certain altitude on my way westward into Mena, Arkansas, there were no ground stations that could pick me up. It wasn't until a half hour later when I re-emerged from the mountain range that surrounds Mena and climbed high enough to hit a ground station, that the dots resume. The line connecting the dots is therefore completely erroneous, and does not reflect the fact that I flew Northward, landed, and then took off again and came South again before flying to the Southwest.

The final waypoint tracked by APRS was a few miles East of my home field, 52F, as I was entering the 45 degree to the downwind. If I had a nervous spouse watching this track, she might have concluded that I didn't quite make the airfield.

Using a 9V battery to power this device is not an ideal solution. I recently went on a cross country trip that involved 1 1/2 hours there, 2 hours at the destination, and 1 1/2 hours return. I powered the device up on the ground and set it on a ledge in the baggage compartment, verifying that the LED was flashing. When I got home, I checked APRS.FI and it had not recorded a single one of my transmissions on the entire trip. I can only guess that the battery was powering the processor enough to blink the LEDs, but not enough to power the transmitter.

Conclusion
All 3 of these services/products have advantages and disadvantages, and none of them provide 100% coverage to allow all your friends to track your progress if you are VFR.

FlightAware requires no additional equipment investment beyond the transponder you already have, and Flight Following. But it is at best spotty and unreliable for the VFR pilot. It seems to be extremely good at tracking IFR flights.

The annual subscription price of the Spot Messenger makes it worthwhile if you want your friends and relatives to be able to see where you're flying right now, or within the past 24 hours. Of course, as a personal locator beacon, if you are still alive and coherent after an emergency landing, it is going to be even better than the old 121.5 ELT in your airplane, because it transmits your exact location to search and rescue. You can hit a satellite pretty easily from most anyplace in the Spot's published footprint, but not 100% of the time. And the "I'm OK" button is a great aid for notifying your friends when you land, if you don't want to dig out the cell phone and engage in lengthy conversations while you top off your tanks.

APRS has a large number of ground stations, but they are typically only in towns and cities, and don't cover uninhabited areas very well, despite the fact that you're several thousand feet in the air. The advantage is that as a mapping tool you can give ALL your friends, it is more reliable than FlightAware if you are flying VFR. It does require a ham license, which is now easier to obtain since they dropped the morse code requirement. See the ARRL for information about earning an amateur radio license.

I'm looking forward to seeing the Spot Messenger people coming up with a more error-resistant user interface for the buttons and LEDs.

Meanwhile, since I'm a nerd and a gadget-hound, I'll use all 3 methods. It means I now have 5 GPSes in my cockpit (including the one in my ATT Tilt smartphone). And, as most pilots (and all libertarians) will find predictable, the least capable of all of them is the one that the FAA certified. (It's installed in the instrument panel.) These others are much more kewl!
-- Dave Morris, N5UP (FCC) and N6030X (FAA)