Halibut Hangar

Originally Published June 02, 2009; Last Updated December 13, 2009; Last Republished December 13, 2009:

United States Navy joins the search for Air France flight 447—a debris field has been located—estimated maximum water depth is two miles; sea floor topology very rugged.

Web:

• UPDATED 12/13/2009 CNN, Search for Flight 447 data recorders to resume.
• UPDATED 07/30/2009 UPI, French looking for remains of Flight 447.
• UPDATED 07/11/2009 BBC, Air France box search winds down.
• UPDATED 07/02/2009 BBC, Piecing together fate of Air France jet. Excluding a failure of the "black box" beacon itself (i.e. no acoustic signal), it seems incredible that searchers cannot localize its acoustic signal.

• UPDATED 06/27/2009 Scotsman, Search for passengers of Flight 447 ends, race for black boxes goes on.

  Earlier reports (6-15 hours) that the flight data recorder (FDR or black box) had been located proved over optimistic—searcher are investigating a sound but are not able to confirm it is the FDR beacon from the.

  A typical FAA approved pinger or beacon attached to the FDR will send out a continuous acoustic 160.5dB, 9ms pulse at 37.5 kHz for a minimum of 30 days, usually up to 90 days or longer at a slightly reduced dB level.¹

  By comparison a dolphin's sonar might click (ping) around 170dB whereas a modern submarine might ping² at a much higher level of 210 - 220dB.

  Every 10 dB increase is like turning up the volume by a power of ten (10, 100, 1,000...)!

  Submariners know that sound travels about four times faster in seawater than air (say 1480 m/sec versus 340 m/sec, respectively). In seawater sound speed decreases for about the first 1,000 meters then increases linearly with water depth.

• UPDATED 06/15/2009 UPI, Investigators: No explosion on Flight 447.
• UPDATED 06/06/2009 Times of India, France sends nuclear sub to help find missing plane. The submarine Émeraude S 604.
• UPDATED 06/04/2009 Time, Could a Computer Glitch Have Brought Down Air France 447?.

• BBC, Lost jet data 'may not be found'. France sends two deep diving submersibles (perhaps both are Nautiles) to support recovery efforts.

  Contrary to current news accounts it’s very likely larger debris items will be examined—if these items (or other information) are indicative of a bomb, debris will be recovered.

• Reuters, FACTBOX: Facts and speculation surrounding Air France crash

Video:

• AP, Brazil Confirms Air France Jet Crashed in Ocean:
• Reuters, Air France searchers find debris

Wikipedia: UPDATED 06/06/2009 Air France Flight 447

-----notes-----

1. Based on the Teledyne Benthos TSO-C121 FAA approved pinger.

2. A submarine sonar operator might compare the difficulty of searching for the "black box" to randomly detecting and characterizing a very noisy (160dB) and stationary submarine using a single relatively fast attenuating high frequency (37.5 kHz) tonal.

Now imagine a submarine sonar operator's job if the "black box" were very quiet (100-110 dB), non-stationary, evasive, emitting multiple tonals within a wider frequency spectrum (1Hz - 20kHz) and maybe using counter-measures like decoy tonals, noise generators etc.).

As correctly operated modern submarines approach the practical limits (technical and cost) of very quiet even the most skilled sonar technician, aided by neural network software, and massive computing power will have an increasingly difficult job.

Thankfully, we can leave the experts to openly debate the nonproliferation implications. A future where nations' undetectable and undeterrable ballistic missile submarines are silently driving into each other gives new meaning to the term "silent service". Perhaps there are better alternatives?