This question would have received much better response had it been posted in the Tech/Ops forum but I came across it and will attempt to answer your question.
The industry has taken steps to improve the probability of 100% data recovery. First, it had been noted that in the majority of cases where the data has been unrecoverable after an aircraft disaster was due to a post-impact fire not power loss. It was also concluded that in many cases, the post-crash fire was not the short, high intensity scenario covered by qualification to the existing TSOs, but due to a much lower intensity, with substantially longer duration fire. Therefore EUROCAE, included the low intensity fire requirement (10 Hours at 260°C) into ED-56 Rev. A. The NTSB and FAA have also acted in increasing the existing high intensity fire survivability from 30 minutes to 60 minutes (50,000 BTUs, 1100°C) in TSO-C123a and TSO-C124a which superceded existing TSOs. in August of 1998.
Another major cause of unrecoverable data (or a "poor" recording) after an aircraft disaster, is due to broken and/or damaged recorders which were unable to record the necessary information due to an internal or system level fault.
Historically, electro-mechanically-based CVRs and FDRs have suffered in terms of overall reliability and performance due to their basic design. Recording head and tape wear, motor belts and bearings, etc. will degrade over time in the severe environments encountered on commercial air transport aircraft. This cause has been dramatically improved by the introduction of all solid-state crash survivable recorders, where non-volatile memory devices have replaced the electro-mechanical tape based recording systems. Since there are no longer any moving parts in Solid State recorders, basic reliability (as expressed in Mean-Time-Between-Failures) has improved dramatically by at least 5-fold. Additionally, since there are no moving parts in the recording system, there is no degradation over time in the quality of the recording. In the past, the quality of the recording has been greatly effected by where in the "maintenance cycle" the recorder is when data is extracted from it (i.e. if it has been a long time since the last overhaul of the unit, head/tape wear, motor bearing wear, etc., will naturally cause a lower quality recording).
Several recent accidents of commercial aircraft have demonstrated the effect of the Solid State Recorders. The AlliedSignal SSFDR and SSCVRs have performed flawlessly with 100% recovery and no errors in the data. In one particular investigation the NTSB started with a download of the SSFDR contents at 9:00 am and by 1:00 pm of that same afternoon a full animation of the final moments of the flight were available for review.
As a result of the survivability and maintainability of Solid State recorders the NTSB have released Safety Recommendations to mandate solid-state cockpit voice and flight data recorders by 2005, i.e. retrofitting of all tape based recorders to solid-state. Many commercial airlines are already doing this on their own based on economic (cost-of-ownership) arguments.
In 1992, an industry-wide meeting discussed ways to improve the probability of 100% post crash data recovery for both the cockpit voice and flight data information. AlliedSignal proposed that one way was to have combined recorders in a dual-redundant installation (i.e. two separate crash survivable recorders storing both the cockpit voice and flight data information) on the aircraft. Further, these combined recorders should be installed in vastly different locations on the aircraft, such that in a worst case scenario at least one of the recorders would be subjected to a less severe post-crash environment. Aircraft manufacturers agree with this basic philosophy, but have yet to implement a dual-redundant recorder installation on any commercial aircraft being currently produced.
To avoid recurring changes to aircraft interfacing and the recorder itself; a new recording system philosophy is required. This new architecture can be an extension of the existing "Data Acquisition System" as the central processing component, accompanied by multiple high-speed serial interfaces to dual Solid State Digital Data Recorders (SSDDR).
In this proposed new system the crash survivable recorders are reduced to simply recording digital information received on high-speed serial interface(s). The recorders need not know the specific source or type of information being recorded, but simply recording the digital data as it is received under a yet to be defined rule set. The processing of information and digitization would therefore take place in other avionics within the aircraft and transmitted to the redundant recorders. If developed suitably, this architecture can provide the following benefits:
1) Dual redundant Crash Survivable Recorders - Reduces airlines spares and logistic support and provides improved probability of 100% data recovery.
2) Crash survivable recorder need not require modification to meet changes in recording requirements.
3) Lower system cost - data processing and digitization process moved to highly integrated avionics subsystems (instead of the recorders themselves, which are subject to more severe operating environments)
4) Minimizing Installation costs by reducing wiring required for growth systems.
5) Eliminating the need to add other crash survivable recorders for additional information storage
6) Minimize cost impact for the recorder itself. The price of two redundant recorders would only be on the order of 50% more than the total price of today's separate FDR/CVR combination.