Hacker News Board Hacker News, browsed like a classic message board
Live data from Hacker News

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

news.ycombinator.com

Post reply on HN
Print view View original

31–40 of 93 posts

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

#31

Post by stan_rogers »

sp332 wrote: post #11
anigbrowl wrote: post #2

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. Ch…

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.

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

#32

Post by kgrin »

asciilifeform wrote: post #22
cstejerean wrote: post #20

Earlier quoted context omitted.

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.

A more interesting question is why one is not permitted to bring a parachute on board at one's own expense, and why there are not even token provisions for enabling their use in a situation where they might be helpful. Air travel phobia seems to be rooted in the lack of control experienced by the passenger - specifically, in the anticipation of utter helplessness in the event of a crash. A parachute would help with t…

I suspect it's a practical concern if nothing else, having to do with mundane constraints like carry-on sizes. Also, as another practical matter, I highly doubt that the folks with severe air travel phobia would be even remotely trained to use a chute (which requires doing it, more than once!)

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

#33

Post by noonespecial »

simplegeek wrote: post #16

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

The percentage of actual crashes in which a parachute would do anyone any good is likely vanishingly small.

You can't use them when too high up (not enough O2) or too low (not enough time to deploy). Most crashes take place on takeoff or landing.

Of the problems that do happen that would take you through a "jumpable" altitude, you can only make the jump if you 1) have time, 2) have enough airplane left to jump out of. If a big whole ripped in the plane while in flight at 30k feet, you are very likely already unconscious or dead.

There are other issues related to the fact that commercial airliners are not made to be jumped out of at speed. Its difficult or impossible to open their doors during flight (with good reason). Even if you could get them open, there may not be a jump trajectory from some doors that doesn't provide a personal introduction to wing or engine part. Also, you cannot jump and live from a plane going 300 knots. The plane would have to decelerate to near stall to make it safe and if its already crashing, maneuvering at the edge of performance is not likely.

Also, consider that professional and military jumpers are highly trained, in top physical shape, and the landing sites are carefully chosen to avoid injury. As a fun thought experiment, take Rosanne Bar, put her in a small canopy "emergency chute", and drop her, at random, over the Arizona desert. (She was on her way to Vegas, baby). Calculate survivability.

Chutes for everyone would be expensive, heavy and probably only be beneficial in single digit percentages (or even sub single) of all crashes. They would very likely cause more problems than they would solve.

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

#35

Post by shiro »

dcurtis wrote: post #23
anigbrowl wrote: post #2

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…

You only have to transmit data when something is wrong. You can use software to determine when to start sending updates.

There certainly are cases with well-understood causes (e.g. birds flew into both engines to make them stop), but I guess there are cases that originally caused from combination of previously-unknown failure pattern; since the failure pattern understood enough to write a software to detect, it may likely be backed up by some fail-safe mechanism.

I don't know much about aircraft controlling software, so this is only a guess from my experience of general system software crash recovery; usually the hardest case is caused by something I've never imagined to happen.

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

#36

Post by jules »

aconbere wrote: post #28
raquo wrote: post #19

Why don't they make black boxes floatable?

I suspect that a floating object increase the range over which you have to search. If you object sinks to the bottom, at least you know about where it ended up.

Let it send a signal.

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

#37

Post by jdbeast00 »

noonespecial wrote: post #33
simplegeek wrote: post #16

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

The percentage of actual crashes in which a parachute would do anyone any good is likely vanishingly small. You can't use them when too high up (not enough O2) or too low (not enough time to deploy). Most crashes take place on takeoff or landing. Of the problems that do happen that would take you through a "jumpable" altitude, you can only make the jump if you 1) have time, 2) have enough airplane left to jump out of…

i'm sorry but i just don't buy the 'chutes aren't worth it / wouldn't work' argument. i'm confident that in the next few decades we'll have better safety systems in planes, it will just take a few really smart engineers. people will still die in planes, sure, but in the cases where chutes or whatever will help, there will be huge benefits.

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

#38

Post by anigbrowl »

dcurtis wrote: post #23
anigbrowl wrote: post #2

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…

You only have to transmit data when something is wrong. You can use software to determine when to start sending updates.

Remind me not to hire you for anything mission-critical.

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

#40

Post by anamax »

jules wrote: post #36
aconbere wrote: post #28

Earlier quoted context omitted.

I suspect that a floating object increase the range over which you have to search. If you object sinks to the bottom, at least you know about where it ended up.

Let it send a signal.

Why do you think that it doesn't?
Post reply on HN