Magnetic FDR locator beacon

[Interested Passenger]

I know that whenever a plane goes down over water the same question gets asked, 'why is it so hard to find the fdr?'

The two issues are of course the limited range of a transmitted signal under water, and the limited power/duration of a battery powered transmitter.

Given that magnetometers are already used to search for wreckage, and solid state drives replace hard drives, what if a powerful permanent magnet was included in the FDR as a beacon, or even replaced the battery powered transmitter?

The advantages are of course that it won't run out, and even in normal service there are no batteries to worry about. What I don't know is how easy is it to detect a large but steady magnetic field? If magnetometers dragged by a ship can find metallic objects from the distortions in the earth's tiny magnetic field, how would they react to something 100,000 times stronger?

[island_airphoto]

The fluxgate for the aircraft compass might not be happy with this plan.

[Denti]

Which fluxgate? But the backup magnetic compass might be unhappy, still, he works with all the other electronics right around it whereas the recorders are pretty far away usually at the back of the plane.

[peekay4]

It won't work well anyway.

Magnetic field strength diminish very rapidly with distance (inverse cube law). A magnetic field 100,000x "stronger" measured 1m from the aircraft would be barely distinguishable from 100m away, much less 1km away.

And passengers with pacemakers wouldn't be so comfortable in the plane...

[underfire]

Searching with the mag, even right now, really doesnt work when looking for an aircraft, a mag looks for differences in the Earths magnetic field, and there is not enough steel in the aircraft to provide a decent signature at depth.
Searches are concentrated on using multi-beam sonars to image and look for anomalies.
Improvemnts would be continuous broadcast/monitoring of aircraft in flight, longer ping time, dedicated ping per aircraft, better understanding of which frequencies to use for longer distance sensing, battery life, and perhaps an ejectible locator beacon...