Flight 188's black boxes may contain evidence to resolve the mystery conclusively, but they may not. One key issue will be the recording capacity of the cockpit voice recorder, which records sound through several cockpit microphones. Some voice-recorder models can only record 30 minutes worth of data; if that is the case with the recorder on Flight 188, then it is possible the recorder will not tell the full story of what the pilots were up to during the 78 minutes they were out of touch with the ground. One theory already being discussed among experts is that perhaps the pilots fell asleep, and, upon awakening, and knowing that the voice recorder only had a 30 minute capacity, decided to fly around for a while so that the recorder would erase evidence of what went on. But more modern recorders can record up to two hours of sound, and if Flight 188 had such a recorder—which is not yet known—then this theory probably is invalid.
Airplane Overflies Its Destination: Will The Tapes Tell the Tale? - Declassified Blog - Newsweek.com
We'll see...