The flight crew of a chartered Turkish airliner that crashed Feb. 6 off the coast of the Dominican Republic, killing 189 people, allowed the Boeing 757's airspeed to drop so low that the plane stalled and went into an 84-second dive into the Atlantic Ocean, an initial investigative report said yesterday.

The report, based on a preliminary examination of data recorders aboard the plane that were recovered from the ocean bottom Wednesday, said that cockpit instruments told the crew that the airspeed of the 757 as it climbed after takeoff from a Dominican resort was more than sufficient -- 335 knots, or about 370 mph -- but that ground-based radar and other sources "indicated a much lower airspeed."

The one-page report, released by the National Transportation Safety Board in concert with Dominican authorities, offered no reason for the discrepancy between the cockpit readings and the plane's actual airspeed. However, the circumstances raise the possibility of a malfunctioning external airspeed sensor.

There were indications that the pilots knew before takeoff that they had problems with their airspeed instruments but elected to continue. The report said "there were discussions about airspeed indicators early during the takeoff ground run and again after takeoff," although it offered no details as to what was said.

According to sources close to the investigation, however, the cockpit discussion began when the flight crew noticed that the captain's airspeed indicator was registering lower than the co-pilot's; then, as the aircraft gained altitude, the airspeed reading on the captain's panel climbed above that of the co-pilot's. When the two indicators disagree, the pilots are supposed to check a third to clarify the reading, but it was not known if that was done in this case.

One thing that could cause disagreement between the two indicators is blockage in an external sensor called a "Pitot tube," a simple forward projection from the aircraft that measures airspeed through expansion and contraction of an internal diaphragm. However, if the Pitot tube is blocked -- by ice or debris, perhaps -- it will still indicate increasing airspeed as the aircraft climbs because of rising air pressure.

For this reason, pilots are instructed to activate a device before takeoff that heats the tube and keeps it from icing over; crashes on other types of aircraft have been caused by failure to heat the tube.

The report said that flight controls, engines and thrust reversers on the 757 were functioning properly, according to preliminary data. "Also, there is no indication of any unusual weather event or external forces acting on the aircraft," it said.

The insufficient airspeed became apparent minutes after takeoff. "While climbing through 7,300 feet, the sound of the stall-warning stickshaker was heard," the report said. "The airplane stopped climbing and started descending. The stickshaker sound continued for about 84 seconds until the end of data. At the time the stickshaker activated, the recorded airspeed was about 335 knots. Data recorded from ground-based radar and other {recorder} data indicated a much lower airspeed." A stickshaker gives a pilot a warning that a plane is about to stall by vibrating the control column and emitting a loud alarm.

Aside from a Turkish flight crew and a mixed Turkish and Dominican cabin crew, most of the victims were German tourists returning from Caribbean vacation aboard a plane owned by the Turkish airline Birgen Air and leased to the Dominican airline Alas Transporte de Internacional. The aircraft took off from the Dominican resort of Puerto Plata and was to have flown to Frankfurt and Berlin. It was only the second crash of a Boeing 757 in 13 years of production.

Yesterday's report was based on an initial inspection of the plane's flight-data recorder and cockpit-voice recorder; both these "black boxes" were recovered Wednesday from about 7,600 feet of water by the U.S. Navy and flown to the safety board's laboratory here.

The boxes, which were housed in the tail section of the 757, were located Feb. 15 by a Navy-chartered recovery vessel towing an acoustic locater system that could detect electronic "pings" the boxes emit when submerged; a "cable-towed underwater recovery vehicle" later plucked the boxes from the ocean floor. Both systems are made by Oceaneering International Inc., of Upper Marlboro.

The cockpit-voice recorder tapes the last 30 minutes of cockpit sounds and conversations, while the flight data recorder on the 11-year-old aircraft was designed to register 72 different airplane movements, control-surface positions and instrument settings.