Both recorders stopped six minutes before the MD-11 plunged into the North Atlantic off Nova Scotia on Sept. 2, killing all 229 people on board.
"They are on separate power [systems] so...it would mean most likely a very severe power incident," said Dana Doiron, a spokesman for Canada's Transportation Safety Board.
Doiron said the cockpit voice recorder will still be able to provide valuable information about the situation the crew faced.
Without recordings from the last six minutes, however, investigators will never learn what (if anything) the two pilots said to each other after their last communication with air traffic controllers. That conversation ended with the pilots declaring an emergency because of smoke in the cockpit and saying they must land immediately.
Hugh Waterman, a former pilot and retired aircraft safety expert with the U.S. Federal Aviation Administration, said the pilots may have turned off the recorders in an effort to find the source of the smoke.
"Automatically, the system wouldn't work that way," and shut down at the same time, Waterman said.
Experts confirmed a series of irregularities in systems on the plane prior to the last six minutes of flight, the safety board said.
"Developing a valid understanding of these anomalies will require extensive examination of wiring and aircraft components that have not yet been recovered from the wreckage," the board said.
It said the effort to recover wreckage from the ocean floor a task assigned to the U.S. Navy salvage ship USS Grapple could be critical to the investigation.
Divers have located several large pieces of wreckage at a depth of about 180 feet. On Tuesday they brought bags with more victims' remains to the surface, which were taken to a temporary morgue at a nearby military base.
Authorities say they won't begin hoisting large chunks of the plane until human remains are removed. Divers say it could take months to clear the crash site completely.