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Ask HN: Why do airlines still use "black boxes" ?

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11–20 of 93 posts

Re: Ask HN: Why do airlines still use "black boxes" ?

#11

From : http://www.eng-tips.com/viewthread.cfm?qid=246491&page=1 Again, any single box is not the problem. It's the receiving end. Picture the FAA receiving 8000 planes worth of a minimum of 88 data streams at 50 Hz at 12 bytes each. That would be a minimum of about 4 Gbps data stream, and allowing for collisions and whatnot, you're around 20 Gbps datastream capacity. Guess where the hackers are going to concentrate t…

Why does each plane have 88 data streams? Why 12 bytes per stream? Why 50 Hz? That's over 8 kilobits per update, 412 kbps.

With 16-bit precision, you can get 528 sensor updates for the same amount of bandwidth. Let's cut that in half (~250 sensors) and reduce the frequency to 30 Hz, then we've gone from 825 kbps to 274.5 kbps. Multiply by 8000 planes, that's 1.8 Gbps aggregate. With stream compression, a lot less.

Challenging? Sure. But I think even my restatement is too much data. Maybe send data less often if everything is within "normal operating parameters." I bet most sensors don't need 16 bits of precision, or to be updated even once per second. Cut my estimate to 10%, that's <30 kbps per plane, <200 Mbps total. Easy!

Re: Ask HN: Why do airlines still use "black boxes" ?

#12
post #8
post #3

There is constant data sent out by most aircraft already. The black box is for when shit goes very wrong, like when a plane is on fire, out of power, with a big hole in it, falling like a rock and spinning like a top.

I still don't see why only a black box should be used for that. As long as a satellite uplink is powered by a separate external power source, none of these factors will stop a transmission.

or you are flying through an electrical storm...

Re: Ask HN: Why do airlines still use "black boxes" ?

#15

Why don't they make the whole plane out of the black box?

Aside from the usual reasons given (a plane consisting mostly of steel armor could not get off the ground, etc.) it would make no difference to the passengers. Falling to the ground from altitude will kill you even if you are sitting inside an indestructible box, simply through rapid decceleration.

Re: Ask HN: Why do airlines still use "black boxes" ?

#17
post #3

There is constant data sent out by most aircraft already. The black box is for when shit goes very wrong, like when a plane is on fire, out of power, with a big hole in it, falling like a rock and spinning like a top.

The best reply I've ever seen on HN.

Redundancy is good, always. Especially when the cost is negligible compared to the lifetime operating expense of the machine and the costs from any misinformation regarding the last moments of a doomed flight (a Crash that is the Airline's fault mega-screws them in the wallet).

Re: Ask HN: Why do airlines still use "black boxes" ?

#20

Good question. Likewise, I've always wondered why don't they have parachutes in aeroplanes :(

Probably because the majority of passengers are not trained to operate a parachute, attempting to jump out of a plane at 40,000 ft is likely to be lethal even with a parachute, and that having 200+ people orderly jump out of a plane with parachutes while the plane is crashing out of control is unlikely to work.
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