The data is persistent, but the beacons only transmit for 30 days or so.
Yes, I know these things have to be hardened, debugged, tested, and paid for. Still!
Why 30 days only? Why not have an atomic (nuclear) battery that will be able to send out sonic pings for a year?
Why can't the damn thing record audio (and lots of other data) from the entire flight, rather than only two hours?
I think after this crash, blackboxes are going to be redesigned....
I commented on this on a prior thread [1]. There has been push back from the Airline Pilots Association against longer recording duration on privacy grounds:
The Air Line Pilots Association (ALPA) did not support the proposal to increase CVR recording time because the FAA did not propose any increase in the privacy protections regarding the access and use of information recorded on a CVR. The ALPA stated that existing protections are inadequate despite years of its attempts to change the standard.
Running anything on batteries for days takes a lot of batteries. A Raspberry Pi for 2 days for example takes somewhere from 1.5 to 2 kg of li-ion batteries.
That sort of weight starts to be really problematic for a device which needs to survive a plane crash - since every bit of extra mass increases the force with which it hits.
Not that you'd want to carry 17 pounds of plutonium around on an airliner all the time, but power output is not an insurmountable problem by itself.
Sorry but you really don't know what you are talking about. Black boxes are not made to be latest generation hardware and top class storage equipments, they are made to resist and survive and air crash as their first priority. And in most cases (i.e. crash on land, since most crashes occur at take-off or landing) 30 days is far enough to recover the data and the black box.
Note that even without the beacon, the AF Rio flight black boxes were recovered 2 years after the crash, under extreme depths of water.
You could say the same about, say, the body of the airplane or the engines. But we have innovation in those fields (composite materials, exotic metals, etc.).
The point is: 2 hours is simply not enough. The BB should be able to hold the entire flight's data; and our current technology (in terms of processing power and storage capacity) is more than enough to do that. Plus, given that the BB is a modular, independent unit it would be easy to swap out an older BB with a newer, better BB.
In this case (whatever the cause) it would definitely be useful to have the recording for the time the plane went off the planned route but that will probably have been overwritten.
I'd argue that, if we have learned anything from MH370, ensuring blackbox survive in the harshest environments in the planet and stay discoverable for long period of time should be the utmost concerns.
Sadly, it is an arbitrary limit insofar that the pilots union opposes increasing it beyond 2 hours: http://www.gpo.gov/fdsys/pkg/FR-2008-03-07/pdf/E8-3949.pdf
However, I suspect the "pinger" mechanism is very, very simple and completely analog. No logic in its circuit at all. Because having it SURVIVE to ping 30d was the key consideration.
At some point the airline is then asking you to buy more expensive tickets on the grounds that they can find your corpse in the event of a crash.
"Why didn't you spend that money making the plane not-crash?"
Because atomic batteries use RTG cells which convert heat directly into electricity - and that's one of the most inefficient ways of doing it, which means, that for amounts which would be safe to put in an airplane, you would have maybe a couple watts of power, and I doubt you would even get that much. Also, nuclear batteries don't last forever, for them to be producing power a highly radioactive materials must be used,with super-short half lives - a material with a half life of hundreds of years doesn't produce enough heat through radioactive decay. Which means that those batteries would have to be frequently replaced - and as with anything nuclear, the costs would be enormous. 30 days to find the black box after a crash is plenty.
Are you really proposing to have every commercial airliner fly around with a relatively large lump of plutonium?