I wrote earlier on how we might make it easier to find a lost jet and this included the proposal that the pingers in the black boxes follow a schedule of slowing down their pings to make their batteries last much longer.
In most cases, we’ll know where the jet went down and even see debris, and so getting a ping every second is useful. But if it’s been a week, something is clearly wrong, and having the pinger last much longer becomes important. It should slow down, eventually dropping to intervals as long as one minute, or even an hour, to keep it going for a year or more.
But it would be even more valuable if the pinger was precise about when it pinged. It’s easy to get very accurate clocks these days, either sourced from GPS chips (which cost $5) or just synced on occasion from other sources. Unlike GPS transmitter clocks, which must sync to the nanosecond, here even a second of drift is tolerable.
The key is that the receiver who hears a ping must be able to figure out when it was sent, because if they can do that they can get the range, and even a very rough range is magic when it comes to finding the box. Just 2 received pings from different places with range will probably find the box.
I presume the audio signal is full of noise and you can’t encode data into it very well, but you can vary the interval between pings. For example, while a pinger might bleep every second, every 30 seconds it could ping twice in a second. Any listener who hears 30 seconds of pings would then know the pinger’s clock and when each ping was sent. There could be other variations in the intervals to help pin the time down even better, but it’s probably not needed. In 30 seconds, sound travels 28 miles underwater, and it’s unlikely you would hear the ping from that far away.
When the ping slows down as battery gets lower, you don’t need the variation any more, because you will know that pings are sent at precise seconds. If pings are down to one a minute, you might hear just one, but knowing it was sent at exactly the top of the minute, you will know its range, at least if you are within 50 miles.
Of course things can interfere here — I don’t know if sound travels with such reliable speed in water, and of course, waves bounce off the sea floor and other things. It is possible the multipath problem for sound is much worse than I imagine, making this impossible. Perhaps that’s why it hasn’t been done. This also adds some complexity to the pinger which they may wish to avoid. But anything that made the pings distinctive would also allow two ships tracking the pings to know they had both heard the same particular ping and thus solve for the location of the pinger. Simple designs are possible.
Two way pinger
If you want to get complex of course you could make the pinger smart, and listening for commands from outside. Listening takes much less power, and a smart pinger could know not to bother pinging if it can’t hear the ship searching for it. Ships can ping with much more volume, and be sure to be heard. While there is a risk a pinger with a broken microphone might not understand it has a broken microphone, otherwise, a pinger should sit silent until it hears request pings from ships, and answer those. It could answer them with much more power and thus more range, because it would only ping when commanded to. It could sit under the sea for years until it heard a request from a passing ship or robot. (Like the robots made by my friends at Liquid Robotics, which cruise unmanned at 2 knots using wave power and could spend years searching an area.)
The search for MH370 has cost hundreds of millions of dollars, so this is something worth investigating.
Other more radical ideas might be a pinger able to release small quantities of radioactive material after waiting a few weeks without being found. Or anything else that can be detected in extremely minute concentrations. Spotting those chemicals could be done sampling the sea, and if found soon enough — we would know exactly when they would be released — could help narrow the search area.
Track the waves
I will repeat a new idea I added to the end of the older post. As soon as the search zone is identified, a search aircraft should drop small floating devices with small radio transmitters good to find them again at modest range. Drop them as densely as you can, which might mean every 10 miles or every 100 miles but try to get coverage on the area.
Then, if you find debris from the plane, do a radio hunt for the nearest such beacon. When you find it, or others, you can note their serial number, know where they were dropped, and thus get an idea of where the debris might have come from. Make them fancier, broadcasting their GPS location or remembering it for a dump when re-collected, and you could build a model of motion on the surface of the sea, and thus have a clue of how to track debris back to the crash site. In this case, it would have been a long time before the search zone was located, but in other cases it will be known sooner.
Reporting has not been clear, but it appears that the ships which heard the pings did so in the very first place they looked. With a range of only a few miles, that seems close to impossibly good luck. If it turns out they did hear the last gasp of the black boxes, this suggests an interesting theory.
The theory would be that some advanced intelligence agencies have always known where the plane went down, but could not reveal that because they did not want reveal their capabilities. A common technique in intelligence, when you learn something important by secret means, is to then engineer another way to learn that information, so that it appears it was learned through non-secret means or luck. In the war, for example, spies who broke enemy codes and learned about troop movements would then have a “lucky” recon plane “just happen” to fly over the area, to explain how you knew where they were. Too much good luck and they might get suspicious, and might learn you have broken their crypto.
In this case the luck is astounding. Yes, it is the central area predicted by the one ping found by Inmarsat, but that was never so precise. In this case, though, all we might discern — if we believe this theory at all — is that maybe, just maybe, some intelligence agency among the countries searching has some hidden ways to track aircraft. Not really all that surprising as a bit of news, though.
Let’s hope they do find what’s left — but if they do, it seems likely to me it happened because the spies know things they aren’t telling us.