What I had understood before was that the airplane carried an Inmarsat satellite transceiver which remained active, even though certain subsystems that use it (notably ACARS) were disabled. While active, the transceiver communicates with the satellite once an hour (the "pings" at 11 minutes past), even if it has no traffic to send. Failing to disable the transceiver in addition to the other systems would have been an oversight on the part of the plane's hijackers, assuming it was hijacked.
Apparently, Inmarsat had available accurate ping timing data. Combined with knowledge of turnaround delays, this would enable them to calculate the plane's distance from the satellite during each ping. That defines an imaginary sphere in space, which intersects with the earth's surface to form a circular locus of where the plane could have been at the time. Presumably, there were eight such ping interactions, ending with the one at 0811 Kuala Lumpur time. There was no 0911 ping, meaning the plane had either crashed or landed and powered off before that time.
And so we had the northern and southern arcs. These were obtained by cropping the circle based on factors such as how far the plane could have flown in the available time, whether or not military radars, if any, had detected the plane, etc.
Now comes the Doppler data. Apparently, Inmarsat also has an accurate read of the plane's transmit frequency. The extent to which this frequency differs from the nominal frequency would indicate the plane's velocity towards or away from the satellite at the time of the ping.
Today, Chris McLaughlin revealed that Inmarsat had studied the Doppler patterns of normal flights in the same region and concluded that the Doppler data for MH370 indicated that the southern arc was the right one. Hopefully, Inmarsat has it right, and the black boxes will be found before their beacon batteries run out.
One minor correction, which I'd seen an indication of and had suspected from an architectural design point of view: the plane was getting pinged, it wasn't producing the pings. Per The Aviation Herald, which has lots of details today (and isn't behind a pay wall who's visits per month I used up yesterday): http://avherald.com/h?article=4710c69b&opt=0
"During the flight the ground station logged the transmitted and received pulse frequencies at each handshake."
That's in the middle of a huge paragraph describing how they did it in quite some detail, e.g. compared data to other 777s flying that day.
No. Persistence of the data does not require continuous power. But the black box has a battery-powered "pinger" that produces sound to make it easier to find. The batteries for that is only required to last for 30 days.
For communication under(salt)water, you're pretty much screwed with every part of the electromagnetic spectrum apart from visible light, and even that won't work in cloudy conditions or if the emitter is occluded. Sound is really the best option.
Because infrared doesn't work very well in water, and crashes in water are the biggest challenge for finding wreckage.
Airliners also carry emergency locator transmitters† (ELTs), which, when activated by a crash, transmit radio signals which can be triangulated via satellite. However, ELTs do not work underwater. No ELT signals from MH370 were heard.
> It seems very clear that these airplane blackboxes are ridiculously under-specced and underpowered.
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.
> 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.
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.
Why 2 hours isn't enough? We're talking about voice conversation between the crew. Mot of the information meaningful to investigation would happen in a short period of time prior to the crash.
Usually correct I imagine but what about the slow de-pressurisation scenarios where the pilots have passed out and the plane flies until it runs out of fuel?
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.
That's a good point. However I believe low pressurization event is captured by the data recorder. That information, coupled with other events, and the fact that the voice recorder goes silent for 2 hours, would give investigators sufficient clue.
I don't have any inside knowledge of how blackbox works the way it does, but I imagine, like with any critical system, reliability and redundancy trump everything else. I bet the two hour limit is not an arbitrary number but rather result of some lengthy tried and true testing process and debate. Any design decision is a trade-off, no matter how small.
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.
Why can't the damn thing record audio (and lots of other data) from the entire flight, rather than only two hours?
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.
>>Why not have an atomic (nuclear) battery that will be able to send out sonic pings for a year?
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.
Atomic batteries are not at all powerful enough. Microwatts.
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.
They don't have to be microwatts. Galileo, for example, used 17 pounds of plutonium to generate 570W of power at launch, with a half life of about 88 years.
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.
Sticking a bunch of nuclear material on airliners to aid in accident investigation seems kind of counterproductive. Imagine how much more fun the 9/11 cleanup at the Pentagon and WTC would have been if the workers got to play "find the needle in the haystack" with a couple of pounds of plutonium along with all the rest.
I don't understand why the pingers are on continuously until battery depletion. Assuming we can't have them be triggered by incoming sound (making them essentially sonar transponders), why couldn't they be on for e.g. 15 days, then off for a month, on for 7 days, off for two more months and on for 7 days? The power requirements of the timing device are minuscule (my watch needs a new battery every few years).
How would turning the pinger off for a month help? It just means that the search operation stops for a whole month while they wait for the pings to resume. I don't understand how your proposed idea would benefit a rescue operation.
I'd suggest something more sensible. E.g. one ping every Ns for the first 15 days, every 2Ns for the next 15 days, every 4Ns for the next 15 days... oh look, "infinite" duration.
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.
the second biggest issue with the data is that it will have written over some of the information that would have occurred at the time the flight deviated from the assigned course.
It used to be that voice recorders with 30 minute loops, I am not sure if that is still the case.
I suspect the answer is similar to "why don't they stream FDR-data, live, for all flights?".
That being: the airlines feel the cases in which extra measures matter are only a small subset (flights with problems in incredibly remote areas) of a small subset (flights that have any problems at all) and thus not worth the extra cost/complexity/risk to all the other flights.
What I had understood before was that the airplane carried an Inmarsat satellite transceiver which remained active, even though certain subsystems that use it (notably ACARS) were disabled. While active, the transceiver communicates with the satellite once an hour (the "pings" at 11 minutes past), even if it has no traffic to send. Failing to disable the transceiver in addition to the other systems would have been an oversight on the part of the plane's hijackers, assuming it was hijacked.
Apparently, Inmarsat had available accurate ping timing data. Combined with knowledge of turnaround delays, this would enable them to calculate the plane's distance from the satellite during each ping. That defines an imaginary sphere in space, which intersects with the earth's surface to form a circular locus of where the plane could have been at the time. Presumably, there were eight such ping interactions, ending with the one at 0811 Kuala Lumpur time. There was no 0911 ping, meaning the plane had either crashed or landed and powered off before that time.
And so we had the northern and southern arcs. These were obtained by cropping the circle based on factors such as how far the plane could have flown in the available time, whether or not military radars, if any, had detected the plane, etc.
Now comes the Doppler data. Apparently, Inmarsat also has an accurate read of the plane's transmit frequency. The extent to which this frequency differs from the nominal frequency would indicate the plane's velocity towards or away from the satellite at the time of the ping.
Today, Chris McLaughlin revealed that Inmarsat had studied the Doppler patterns of normal flights in the same region and concluded that the Doppler data for MH370 indicated that the southern arc was the right one. Hopefully, Inmarsat has it right, and the black boxes will be found before their beacon batteries run out.