FDR Recovery Difficulty
The investigation report on UA93 states the CVR was recovered 25 feet below ground. It does not say it was in the crater on top of the earth - it was under 25 feet of earth. Assuming this aircraft struck ground at nearly the same speed, it would indicate the possible difficulty in finding the memory module. I addition, the impact was apparently into the side of a ridge, not at the bottom of the valley where much of the debris was recovered. If it was into the side, the impact would have dislodged a great deal of earth with which the data module is intermixed. It would be a surprise if it was recovered quickly.