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Potentially dumb question about airplanes

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Jrazz posted 3/9/2014 19:50 PM

Why isn't "black box" data transmitted automatically to a land-based site? When there are (rare) crashes, everyone's scrambling to find the black box. Can't the data be translated into something simple and instantaneously transmitted to a satellite or control tower or something?

Just thinking out loud.

MovingUpward posted 3/9/2014 20:22 PM

Possible reasons are the following.

Lack of a data collection structure as the data would probably be beamed down to towers and would have to switch as it traveled much like your cell phones.

Another reason that is more plausible is the amount of data that is collected that would need to be transmitted and the number of planes dumping that information.

Another reason is if the communications go down then you have no way to transmit the data where as the black box is tied directly into the plane. it is one degree of separation closer than if you transmit the data.

Jeaniegirl posted 3/9/2014 20:31 PM

Too bad they can't manufacture planes out of the same materials black boxes are made of.

LovesLaboursLost posted 3/9/2014 20:52 PM

^^right? If it's supposedly indestructable...

Dark Inertia posted 3/9/2014 21:40 PM

I am guessing you are wondering this in light of the Malay flight that disappeared? That whole thing has made me so sick my husband has asked me to stop checking the news about it. Plane crashes always upset me so badly.

[This message edited by Dark Inertia at 9:40 PM, March 9th (Sunday)]

TrustedHer posted 3/9/2014 22:34 PM

Well, this falls into my court, as an IT guy who does VHF and HF radio as a hobby.

The black box records lots and lots of data, including the voices from the cockpit, all the monitoring data from the instruments, settings of controls, airspeed, etc.

Airplanes typically don't use HF radio at all; most of the ATC (Air Traffic Control) conversations happen over VHF, which is short range. There are only a limited number of VHF channels available, and they are all full already, with voice co-ordination of the aircraft movements and status.

Since VHF is short range, it wouldn't do any good to send data over it anyway, for flights going over the ocean or unpopulated areas.

HF has more range. But with that range, you get limitations on data bandwidth; you can send digital data, but it is very low capacity, and error-prone. It's hard enough to send one voice stream, and there's lots of technology in use to get that through.

There's no way to get a huge amount of data through those pipes.

Now that there are satellite links on planes, that's an option. But that's new technology, and actually quite expensive, and it has bandwidth limits too. And outages.

If you've ever used the inflight wifi, you get a sense how limited it is.

I imagine they will move to satellites over time, if it gets cheaper. Just realize that the major airlines have a commercial interest in fitting their planes, and it's taking them years to do their fleets.

As you pointed out, the crashes are rare, and the black boxes are there mainly to determine what happened after the fact. Since the investigations take months and months anyway, they figure they can wait.

Jrazz posted 3/9/2014 22:39 PM

Cool, thanks everyone! TH, loved the technical breakdown.

UnexpectedSong posted 3/9/2014 23:49 PM

Too bad they can't manufacture planes out of the same materials black boxes are made of.

If they did, the plane would be too heavy to fly.

purplejacket4 posted 3/10/2014 23:48 PM

T/J trustedher did you see Non Stop? I was just wondering how much of that was plausible. It scared me so bad I'll have to either have a stiff drink or a Xanax for my next flight.

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