The nation's airlines are being told to examine the takeoff warning horns on two of the industry's most widely used jetliners after faulty alarms were found in 35 of the aircraft.

The inspections on nearly 1,800 Boeing 727s and 737s, which were ordered Thursday by the Federal Aviation Administration, comes as federal accident investigators continue to try to determine whether an alarm may have failed on a Delta Air Lines Boeing 727 that crashed last August at the Dallas-Fort Worth airport.The alarm is designed to sound if a pilot has forgotten to prepare an aircraft properly for takeoff, such as leaving wing flaps, which help give a plane lift, in the wrong position.

The National Transportation Safety Board has said there is evidence, though not conclusively determined, that the flaps may not have been in the proper position on the Delta jet, yet a cockpit voice recorder tape shows the alarm did not sound. The NTSB investigation into the crash, which killed 14 people, is not yet completed.

As a result of questions surrounding the Delta accident the FAA last month ordered a one-time "purely precautionary" check of the takeoff alarms on nearly 1,200 Boeing 727s. The agency announced Thursday that in 35 cases, the alarms either did not work or worked improperly.

"This condition, if not corrected, could result in an attempted takeoff with the airplane in the improper configuration and with the takeoff warning system inoperative," the FAA told the airlines in its special airworthiness directive.

The FAA said 29 of the jets with defective warning systems belonged to three airlines: Continental Airlines, with 17; Eastern Airlines, eight; and Delta Air Lines, four. United Airlines and Federal Express each had two planes with faulty alarms and Orion Air and AmeriJet International each had one, the FAA said.

The airlines were ordered to conduct "repetitive testing" of all the alarm systems including the "repair and replacement of inoperative components if necessary" on the 727s as well as Boeing 737s which the FAA said had a similar system "subject to similar failures."