How British satellite company Inmarsat tracked down MH370
telegraph.co.uk
telegraph.co.uk
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.
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?
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 used to be that voice recorders with 30 minute loops, I am not sure if that is still the case.
The data recorder will cover the entire flight.
[0] http://www.sea-avionics.com/lc/cart.php?target=productDetail...
Granted that is a lot more fragile then a plane black box but still. There should be a way to record a lot more then 120 minutes.
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.
https://www.youtube.com/watch?v=mQehX0rVYuY
Check out his other videos as well. He is really good at what he does, and his videos still retain the hackery feel.
"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.
http://www.reddit.com/r/MH370/comments/218i36/how_the_satell...
engineers were able to narrow the location of the plane down
with an initial analysis of the Doppler effect on the signal
from the flight’s pings and the plane’s approximate altitude.
I wonder if they flew test flights along both arcs and compared the data.
No, but they compared the present data with recorded data from other flights along the same routes for comparison.
So I'm guessing they extrapolated from routes that were in that general direction, like Sri Lanka - Perth.
It's likely there's a lot of assumptions at work in their calculations, but it might be good enough.
But apparently, their hardware is installed on plenty of airplanes, so they just needed to study normal flights north and south in the region to establish a baseline to which to compare MH370's data.
And it was that data that lead them to conclude that the southern route was likely the one MH360 actually took.
Also curious how they matched it to planes flying the southern route, since I wouldn't have guessed there were any other planes flying on the southern route (which goes...nowhere).
Logged ping, base carrier frequency 1375.003762 MHz.
Logged ping, base carrier frequency 1375.003761 MHz.
Logged ping, base carrier frequency 1375.002961 MHz.
Then with some maths and comparing to the known positions of the plane (pre-contact loss) and known positions of the satellite you can work out which way the plane would have had to move to get the observed results once contact was lost.
(numbers in example made up, and likely aren't appropriate for satellite communications but you get the idea)
The pings, as I understand it, came an hour apart, and continued for 7-8 hours total. With just the pings themselves they were able to extract the distance from the sat, which is what led to those arcs they published last week. I dunno if doppler shifts from pings an hour apart add much to that.
Would the satellite always relaying that level of precision to the ground? If it is, why would they have prioritized that over what would have presumably be a dramatic increase in capability if it were discarded instead? Could they have designed it to store that much precision in rotating logs available on request? And furthermore, how is a relativistic Doppler shift on those magnitudes discernible from the frequency shift naturally occurring from the plane's transmitter?
I suppose my point is that while it's easy to understand the idea of a train whistle changing pitch as it passes by, how they would do it in practice sounds like magic, being unfamiliar with the capabilities and the equipment that geostationary satellites generally carry.
However, given the corridors, it still seems like the suggestion is that the Doppler measurements said it was moving rightward or leftward, when it should only say how much the aircraft was getting closer or getting further away. Looking at the map alone, it doesn't seem like that information would help distinguish which corridor it was in.
Even if it isn't intentional, in scenarios such as measuring a Doppler shift I can see how it can be a useful tool. Almost analogous to microsaccades we make with our eyes.
** is thought to have tracked down.
It's almost a certainty that the US government has spy satellites video recording the entire planet at all times, at a level good enough to distinguish individual aircraft. The US spy agencies probably knew where the plane was right away, but they can't just tell everybody or the jig is up.
So they may have just contacted this satellite company, told them where the plane is, and came up with a technical explanation of how it was located.
On the other hand, if it is storage and downlink bandwidth that is limited, sats would probably be programmed to ignore or discard uninteresting signals. This seems likely to me.
So the question may be whether commercial airliner pings from the southern Indian Ocean area were considered 'interesting' at the time and, if not, did anyone realize there was a rogue 777 in time to re-task the satellites?
Regardless, I'd bet those signals are considered interesting going forward.
Down-links are ( depending on generation and usage ) either from one of an array of narrow-beam antennae on the Inmarsat or from the wide-area general broadast antenna; much easier to intercept, you and I can do it with a sat-TV dish and an RTL dongle.
the fact that none of these countries gave information about the whereabouts of the plane in a timely fashion suggests to me that they have a vested interest in not sharing what they know.
It's almost a certainty that the US government has spy satellites video recording the entire planet at all times, at a level good enough to distinguish individual aircraft. ...
You are a conspiracy nut. :-)
Spy satellite time is expensive. And they typically have a narrow field of view (the better to read the license plate number off of your car). Basically they are orbiting telescopes like the Hubble, except they are pointed down instead of up.
It is inconceivable to me that they'd waste time having a spy sat looking at empty stretches of the Indian Ocean for no good reason. Especially when there are more interesting things to look at (Afghanistan, Ukraine, North Korea, etc.).