3G vs 4G

3G refers to third generation cellular telephone data transmission techniques, and 4G refers to, you guessed it, fourth generation. A new generation appears about every ten years or so. 4G started appeared a year or two ago. 4G is roughly ten times as fast as 3G. That's nice. Why do I care? I don't even have a cell phone. I don't really, but it might upset the aircraft instrumentation apple cart, at least for private airplanes. I realize that in the grand scheme of things, it is not really a very big apple cart, but it is a bit of a revolution, technology wise.  

BBFlight has an app for your tablet that can provide not just navigation aids in the form of maps, but also some basic aircraft instrumentation like compass, altimeter, artificial horizon, and airspeed indicator. I was a bit nonplussed when Marc told me about this today at lunch. How could it possible maintain an artificial horizon? I know smart phones have accelerometers that allow them to tell what angle they are at, but that isn't going to help in an airplane. When making a properly banked turn in an airplane, down is going to be down relative to the aircraft, not the earth. Artificial horizons use gyroscopes as a reference. Gyroscopes on gymbals maintain their orientation regardless of which way "down" appears to be.

Seems BBFlight's software is doing inertial navigation. It watches the accelerometer constantly, and can tell when you turn or bank or change speed either horizontally or vertically. It starts on the ground and keeps track of every move you make, and by keeping a running summation of these moves, it can tell where you are and what angle you are at. Commercial aircraft using similar technology can fly from New York to London and know their location to within six feet.

Tablets not only have cell phone connections, but they also have GPS, which can tell you where you are, so the program can compare the location it has determined inertially with what the GPS tells it.

We can determine speed using our old friend "rate times time equals distance". If you know where you were five minutes (or five seconds) ago, and you know where you are now, it is a simple matter to compute your velocity. Of course, this is land based velocity, not your airspeed, which could be substantially different. You probably will still want to have a real airspeed indicator.

GPS can also tell you your altitude. So you can do away with your altimeter, which is probably wrong anyway being as it is based on air pressure, which is always changing.

So what's this all got to do with 4G cellphone communications? This same program from BBFlight can also display maps on your tablet. As you fly along, the maps are updated on the fly, so to speak. If you are flying in a circle looking for a place to land, like an airport, a tablet that only has 3G communications can't keep up. You get a map, but you are turning, so it needs to update the map, and by the time it has the update, you have turned even more so what you are seeing is a very jerky video. With 4G the map rotation is perfectly smooth.

Rumor has it you can get cell phone coverage all the way from San Francisco to Portland (Oregon). I expect it's good anywhere along the I-5 corridor. 100 miles East it might be a different story.

As for the apple cart: this program will run on an iPad or any Android tablet. The aircraft instruments they replace cost thousands of dollars. It will be a while, probably a long while, before this tablet type instrumentation is accepted by the aviation community, and probably even longer before the FAA approves it, but it will happen.

Update November 2021 replaced missing image.