A bit premature, but in the hope that this incident gets to this phase, here's some data on recovery of flight recorders and underwater locator beacons (ULBs).
The Wikipedia page on ULBs
https://en.wikipedia.org/wiki/Underwater_locator_beacon
links to this 1968 FAA report:
http://www.fire.tc.faa.gov/pdf/na68-7.pdf
"Background
Certain types of commercial transport aircraft are required by regulation to carry airborne flight data recorders for accident investigation purposes. A number of airborne recorders and their records were never located following a crash, especially after an aircraft crashed into water. The CAB requested the FAA to conduct a study for possible solutions to aid in locating the recorders and/or the recorded records from submerged aircraft. Following a crash in 1965 in which a flight recorderr and its record were lost in water and never recovered, the CAB formally requested the FAA to require commercial carriers to install acoustic-type locating beacons on all flight data recorders that are carried for crash investigation purposes."
The report talks about acoustic propagation through aluminum honeycomb fuselage structure, which may imply that was a consideration that drove the ULB acoustic frequency selection.
A set of slides describing at-sea recovery:
http://www.irs.uji.es/2nd-i-auv/pres...ert-Thomas.pdf
Slide 13 lists time to recover flight data recorders for a number of at-sea accidents.
Table 4 of the Metron report on AF447 has a more comprehensive summary of at-sea accident recoveries.
http://www.bea.aero/fr/enquetes/vol....h.analysis.pdf
Description of Table 4 in the Metron report:
"Table 4 below highlights data on 27 aircraft crashes at sea that were assembled by the BEA. Of the aircraft involved in these crashes, 25 were fitted with 2 ULBs while two had only one. The crashes involved 52 ULBs of which only 5 failed to function. This indicates a more than 90% survival rate which is higher than the 80% assumed for the underwater search analysis in section 4.3.1. The failures in the table include those of the ULBs onboard the South African Airways Flight SAA 295 which were likely to have been caused by an in-flight fire. With this in mind, the estimate of 90% survival rate for the ULBs may itself be low for a crash at sea that does not involve a fire."
While there appears to be some trend between depth and days to recover, there are exceptions, such as Air India 182, 23 June 1985, where the recorders were found 17 and 18 days later at a depth of 3250 meters.
For those cases with depths greater than a kilometer, half (4 of 8) had recorders recovered in less than 30 days. Of 27 cases in the table where at least one recorder was found, only 6 were found after more than 30 days, and only 3 after more than 90 days. The last 3 were all deeper than 1 km.
The design parameters of existing ULBs are close to the specs in the 1968 FAA report. One could argue that the 90% ULB reliability figure cited by Metron does not imply a need for any drastic changes to the ULB design (e.g., frequency).
The FAA appears to have been responsive to the BEA recommendation from AF447 to extend the battery life of ULBs. A 2012 notice of Revision B to TSO-C121:
Federal Register, Volume 77 Issue 43 (Monday, March 5, 2012)
This includes a number of interesting comments from industry.
Also being adopted in Europe:
http://www.easa.eu.int/rulemaking/do...0Issue%203.pdf