Quote Originally Posted by Belly Buster View Post
One is that it only holds 2 hours of data. If the last 2 hours were just gliding into the sea, that's useless.
It would record not just changes for the last 2 hours but the state of the craft and its sundry systems for the last 2 hours, which would be profoundly useful.

Second - if the plane was deliberately sabotaged by the pilots, they could have pulled the circuit breaker for the black box which again would render it useless.
A question that profound being answered under these circumstances is the literal opposite of useless.