If A Popular Malaysia Theory Is Right, Half The Black Box Data Will Be Worthless

NTSBAn NTSB official with the flight data recorder from Asiana Flight 214, which crash landed in San Francisco in July 2013.

If Malaysia 370 crashed into the Indian Ocean, its two black boxes would almost certainly have survived, and will be crucial to finding out what happened to the plane with 239 people on board.

But the bizarre circumstances of the Malaysia situation could render much of the information they reveal totally useless.

One of the two devices, the cockpit voice recorder (CVR), records the pilots' voices, air traffic control, and other noise in the cockpit.

The problem is that it's designed to hold onto only the final two hours of the flight. Until an FAA rule change a few years ago, it held just 30 minutes.

Two hours is plenty in "standard" crashes, which usually happen quite quickly. But if one popular theory turns out to be right, it's not nearly enough.

In a Google+ post, Chris Goodfellow theorized that smoke filled the cockpit, maybe from a burning tire on the front landing gear. He suggested that the pilots then turned the plane toward an airport that could handle the 777, turned off the transponder along with other electronics in an effort to isolate the source of the fire, and were then overcome by smoke.

If Goodfellow's right, the CVR will include two hours of silence and reveal nothing about the pilots' final moments and decision making. If the plane was hijacked, then crashed several hours later, investigators won't have potentially crucial audio of the takeover.

The second black box, the flight data recorder, tracks of a wide range of parameters, including speed, altitude, engine power, and flight controls, and holds 25 hours of data. It does not, however, hold voice recordings from the cockpit.