Re:Ask HN: Why do airlines still use "black boxes" ?
by stan_rogers on Wednesday June 03, 2009 @05:16PM
(#640439)
More than once per second (in fact, more than many times per second) means the difference between FOD ingress failure mode and, say, a spontaneous single blade failure in a turbine, between a synchro follower field inversion (think of a compass needle flipping around in an electromagnetic coil forcing the table it sits on to try to re-orient itself to the new reality) and a hard manual input, between externally-induced overtemp and a fire starting in the monitored system, not to mention vibration-induced momentary shorts playing all kinds of hell on both digital and analog control systems.
People really ought to try to grasp how quickly things can go wrong in the real world, and how difficult it can be to tell what made the nice shiny silver bird look like the crumpled foil discard of a cigarette pack smeared with a poorly-preserved meat jelly. You only have to see one used-to-be jet (complete with used-to-be pilot) before you start wondering how anyone could make sense of it -- and that's with the physical evidence in hand.
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!