ROMULUS, MICH., NOV. 18 -- The Federal Aviation Administration began reevaluating its criteria for computerized takeoff warning systems after the Northwest Flight 255 disaster, an FAA official told a hearing into the crash today.

Harold Wasinger, supervisor of the FAA's aviation and electronics section in Long Beach, Calif., said the agency may designate the cockpit warning system as "essential" because of the Aug. 16 crash that killed 156 people at Detroit Metropolitan Airport.

The National Transportation Safety Board, which is conducting a hearing into the crash, which was the nation's second-worst air disaster, has compiled evidence indicating that the wing flaps and slats on Flight 255 were not properly set to provide lift for takeoff.

Investigators also have said there is evidence to suggest that the crew of the Phoenix-bound jetliner did not receive a computer-generated voice warning of the improper flap and slat settings.

Wasinger said the Central Aural Warning System (CAWS) aboard the MD80 version of the DC9 currently is not classified as "critical" or "essential" under FAA rules.

"A critical system is one that is performing a function on the airplane and as a consequence of failure of that function the airplane is lost," Wasinger said.

He said one reason CAWS is not considered critical is that there are other systems to warn the crew of problems before takeoff. But he said the Detroit disaster has prompted a review of the classification.

"The FAA, as a result of the Detroit accident, has formed a special team, which is now making an evaluation of that situation," he said.

If the FAA determines the system is essential, a backup will be required in the event of its failure, he said.

Wasinger said the special review committee will "evaluate the entire subject of takeoff warning to determine whether its original assignment of criticality was correct."

Earlier, a Northwest pilot who flew in the jump seat aboard the doomed aircraft as a passenger on an earlier flight from Detroit to Saginaw, Mich., the day of the crash told the NTSB panel that the takeoff warning system was operating properly.