Using a GPS-Watch on board
In summer 2009 I started taking a GPS-watch on all my flights. The watch is a GlobalSat GH-625m, which is basically designed for running and othe outdoor sports.
Its main competitors are the Forerunner-watches of Garmin. However, they're a bit more fixed on sports and therefore might not use as many functions when used for flying. I need to stress though, that the Garmin watches are far more popular and that they seem a bit more mature.
The GlobalSat watches still have some minor errors and glitches. However, the tech team is constantly working on the watches and frequently releases software updates. In addition, they're very open to ideas and suggestions by customers.
First off: Overall I'm very happy with my watch. It did very well on all my flights despite definitely not being designed for that.
Using GPS on an airplane
Generally, using a GPS on a plane should do no harm to the plane or the security on board, since the GPS device does only receive data and not send anything itself. Because it doesn't send, it has no way of interfering with instruments in the cockpit. Secondly, GPS is also used up front in cockpits, so it is a save and common technology used in aviation every day
I know many airline pilots who use their own GPS device in the cockpit or allow passengers they know to place theirs in the cockpit. However, some airlines prohibit GPS on board of their planes. So to be sure, inform yourself first before flying.
I can not be held responsible for anything having to do with using a GPS device on an airplane, may it be damage to the device itself, it being taken away, or any charges of airlines for usage on board!
Satellite Fix
In order to be able to know and log its position, the watch needs to have contact to at least 4 satellites. First establishing this contact after a longer downtime (of more than 2-3 hours) can take up to 3-5 minutes and should be performed outside and possibly when standing still. It's best to do this before entering the terminal building. Thereafter, you can switch the watch off again.
When you're seating down on your window seat in the airplane, the watch has no problem finding the satellites again. Most of the time it found way more than the required 4 satellites (see how many are marked black in the photo below!)
The watch even managed to establish a connection when I had a window seat, but no window in my row (only in the rows before and after). Even when the persons in these rows closed their window blinds, it didn't really matter to my watch!
Contact seemed to be a bit better on B737 and CRJ planes, and a bit less good on the MD-11. On my two transatlantic flights, the watch both times lost contact in the middle of the ocean, but re-established it again afterwards. As can be seen on the photo above, most satellites are located around the middle of the planet, with not so many up in the far north. That's why it is better to sit on the southern side. However, I still had no problems establishing a connection even from a seat on the northern side of the plane.
Overview of functions
So what can the watch do in addition to saving the position every second?
Working with fix points
The watch can save 100 fix points. These can either be entered on the watch directly (a bit tedious) or uploaded from your computer. These points can be used in two interesting ways:
- First you can greate a "go to" to a single point, or create whole routes consisting of multiple points, and observe as you're proceeding. The watch will show the remaining distance and time to the next point. While the distance is always about 5% too high, the calculated time is quite exact.
- Secondly, you can use these points to see where you're flying, as these points are shown on a simple navigation display.
Below are two photos of this: On the very left you see the map mode, which shows us passing "between" Manchester (EGCC) and London (EGLL). On the right it shows the remaining distance to our destination, Amsterdam (EHAM). The photo on the right hand side pictures the "go to"-option. It shows the actual heading, the heading to the next point, as well as the remaining distance and time to get there. As you can see, the time is pretty exact!
Note: The dotted lines above EGCC are some kind of error, which only showed up on long flights. However, they're only present on the watch display, not in the log file on your computer. So don't worry!
 
Displaying flight data
The watch can display various flight parameters. You can create four different "pages", and fill them with up to four different data sources each. This can be done directly on the watch. For flying I created a display featuring speed, altitude, vertical speed and remaining distance. Unfortunately, there are still some flaws here:
First there are the units. Up to now you can choose between metric, statue miles and nautical. Nautical will provide you with distance in nautical miles and speed in knots, but the altitude is also displayed in miles instead of feet. I asked the developers for an aviation mode and I hope they'll include it in the next update.
Speed is displayed pretty accurately. However, at the moment, the display starts from 0 again after passing 655. This only happens on the watch display - the logged speed is correct. I hope this is corrected soon. As you can see on the photo, the measurement is pretty accurate (280 + 655 = 935).
Altitude: The displayed altitude is always about 500-1'000ft too high. But this isn't really the watch's fault, since measuring altitudes with satellites just isn't that great. But knowing the standard flying altitudes for the regions you're flying in, you can just round the data to this and you should be fine most of the time.
Vertical Speed: I can't really judge the correctness of this one, since up to now it is not available in ft/min. However, it seems that the display is not continuous but only offers certain steps, like -14, -18, -22, etc. This isn't so much of a problem though, since you can easily find out your vertical speed afterwards when looking at the log file on your computer.
Remaining distance: As mentioned above, the distance shown by the watch is always a little too high, even more when considering that the watch goes direct and the plane is bound to airways. However, since the deviation isn't that big and you can always find out how long your trip was afterwards, it's ok.
Analysis
The saving of the position is extremely accurate, particularly if the watch is in contact with more than 4 satellites. Just look at the taxiing in Zurich - not too bad, huh?
Of course, the data can also be displayed in 3D, for example in Google Earth. This is a half holding followed by an ILS-Approach in Zurich.
You can also process the file with various programs. I especially like "GPS-Track-Analyse.NET" . Its core is the list of all track points, together with graphics of altitude and speed. Here you can also find out your vertical speed pretty easily (see circle in photo). The program can be switched to aviation mode, with all the correct units.
If you like, you can also have a look at your flight in 3D here!
Finally, here are some of my flights in Google Maps you can have a look at!
Of course there are many more possibilities of what to do with your GPS data
The only limiting factor is the battery: Battery life is only about 7 hours. But it is no problem to reload the watch even when recording data, and the reload takes under an hour. Therefore I recommend taking an USB-loader on your longhaul flights.
All things considered, the watch indeed is a nice gimmick that provides some fun inflight as well as afterwards!
I wouldn't want to fly without it anymore!
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