On the note on recorders, an interesting paper was published this year on Recovering Data and Voice Recorders Following At-Sea Crashes.
I can't link the paper, but i'm posting the abstract below. If anyone wants to read the whole thing, send me a PM and i'll email it to you.
Abstract – The international aviation safety community has
concluded that existing methods of blackbox localization and
recovery are not effective in deep ocean situations, and
occasionally not effective even in relatively shallow water when
the acoustic pinger is buried or covered in debris. The majority
of these pingers are provided by two companies, Teledyne
Benthos and Dukane, according to pre-determined form and
function, and these devices are essentially “built to spec.” The
purpose of this paper is to identify the shortcomings in the
existing, decades-old functionality and to recommend the
introduction of acoustic modem technology to provide orders of
magnitude improvement in blackbox localization and data
recovery.
Fundamental ocean physics clearly indicates that the
following conceptual changes should be considered:
1. The current pinger technology operates at nearly 40 kHz
frequency. Simply reducing the frequency to perhaps 12
kHz will substantially increase range in seawater and
even improve performance when the device is covered in
sand or debris.
2. The devices use very short sinusoidal tones (usually
called tonals) as their signals. Ocean propagation often
is highly selective in frequency due to the constructive
and destructive alignment of propagation paths – some
frequencies are supported, others are canceled.
Furthermore, it is difficult to transmit sufficient energy
into the water with these signals.Tonals are very poor
candidates for robust, reliable ocean signaling.
In addition to fundamental issues, the current system
operates by a water-activated commencement of repetitive
transmissions (pings) of these short tonals the moment the device
enters the water – even though no listening devices are present.
This is a waste of energy.
In this paper, we provide a brief overview of acoustic
propagation from the perspective of its differences with more
commonly understood radio frequency (RF) propagation. We
follow that with our suggestions for substantial changes in
operational concept, specifically arguing for wider bandwidth
waveforms with more sophisticated receiver processing.
However, given the effort to utilize more complex systems, we
recommend they be further adapted to support underwater
acoustic communications (acomms). This will provide blackbox
and crash recovery far more effectively than is now possible, and
can support data recovery when the devices themselves cannot be
recovered. In particular, acomms modems can be used in support
of long-range, accurate position estimation by either manned or
unmanned platforms. Our proposed system will be somewhat
larger than the present system, but it will significantly enhance
the ability to find a submerged black box.