By John Crawley WASHINGTON, Feb 8 (Reuters) - The tail fin of an American Airlines (AMR) jet was likely under enormous stress before it snapped off the aircraft, which then plunged into a New York neighborhood last year, killing 265 people, investigators said on Friday. Preliminary engineering and other analysis of the crash of Flight 587 last Nov. 12 shows the Airbus A300-600 was moving straight at 290 mph (465 kph) with its nose pointing 10 degrees left of center. In addition, the plane's rudder was deflected to the right. The National Transportation Safety Board said Airbus engineers determined that that combination produced forces on the right side of the tail fin, also called the vertical stabilizer, that might have exceeded design standards. The fin and rudder broke off the wide-body jet before it crashed into a residential area of Queens shortly after takeoff from John F. Kennedy International Airport. All 260 people on the plane were killed as were five on the ground. The latest information has investigators probing deeply into the jet's complex flight control system. It also was the basis for new safety recommendations for pilots on rudder use. HIGHLY UNUSUAL RUDDER MOVEMENTS Investigators are focused on at least three full and highly unusual rudder movements in rapid succession in the final moment of flight. The safety board still does not know if the crew commanded them or if the rudder moved as a result of a mechanical malfunction. Pilots generally use the rudder during flight to position the nose of the aircraft while turning. Other flight controls actually turn the plane. The safety board said it was investigating a handful of incidents involving A300 flight control problems, including one about a week ago on a FedEx (FDX) cargo plane. That plane was undergoing maintenance checks when damage to the rudder system was found. With the crash probe focusing closely on the plane's rudder, the safety board issued new guidance on the aggressive use of flight controls in certain situations. The board recommended that regulators make airlines and manufacturers tell pilots that maximum rudder movement can be achieved with only light touches on the rudder pedal when the plane is traveling fast. The recommendation also would advise pilots that full or nearly full movements of the rudder in one direction followed by similar movement in the opposite direction while the plane was in the same general configuration as Flight 587 could put excess forces on the tail fin. Dozens of Airbus (EAD) (EAD) pilots at American Airlines want the carrier to ground its fleet of 34 Airbus A300 aircraft, saying the accident probe had raised too many safety questions about the planes. Marion Blakey, the safety board chairwoman, said on Friday there were no plans to recommend that the carrier's A300 fleet be grounded. The board will not determine what caused the crash for a year or longer.