The Federal Aviation Administration ordered airlines Friday to check takeoff warning alarms on all Boeing 727 jetliners because of questions raised in the investigation of a Delta Air Lines crash last month in Texas.

FAA officials said the directive to the airlines for a one-time check of the estimated 1,200 jetliners being operated in the United States was "purely precautionary." They insisted there is no evidence at this point to indicate the alarm, which warns of a false flap setting, malfunctioned in the Delta plane. Investigators have uncovered conflicting evidence as to whether the flaps were positioned properly.Boeing spokeswoman Liz Reese said Friday in Seattle that the company was unaware of the FAA order but added that the order is not unusual.

A federal investigation has yet to determine what caused the Aug. 31 crash at the Dallas-Fort Worth airport, which killed 14 of the 108 people aboard the plane bound for Salt Lake City.

But National Transportation Safety Board investigators have said that among the areas being examined is whether the flight crew extended the flap setting as required. An alarm in the Boeing 727 should have sounded in the cockpit if the flaps were not extended for takeoff as required, but no such alarm could be heard on the cockpit voice recorder tape.

An aircraft's wing flaps help the plane gain lift and should have been extended 15 degrees when the Delta jet took off.

The lever that controls the flaps in the Delta jet was found in a "retracted" position and the flaps on the wing also were found retracted. However, the co-pilot was heard on the cockpit voice recorder tape to acknowledge that the flaps had been set at the 15 degree position.

Sources close to the investigation emphasized that nothing has been developed yet to explain the conflicting evidence.

Among the theories being examined is that the flap setting might have been called out but not set properly. Another theory has been that a crew member might have extended the flaps properly prior to takeoff, but at the last second retracted them in a desperate attempt to reduce drag and keep the plane aloft.

Anthony Broderick, the FAA's associate administrator for regulation and certification, said the directive to check the alarms on the Boeing 727s was precautionary and "not anything other than our own effort to gather data."

Broderick said the action was taken because there have been "a lot of questions asked" in connection with the crash and the positioning of the flaps during the takeoff.