NTSB To Pilots: ‘Watch Your Tail’
By Howard Schwach
While the National Transportation Safety Board (NTSB) is still reporting that the investigation into the crash of flight 587 in Belle Harbor three months ago may well take several months more to complete, the agency has issued a "safety recommendation" that warns pilots that sudden swings of a jet’s rudder could cause a tail fin to separate from the aircraft, precisely what happened to the Airbus A300 that crashed into Rockaway.
"Certain rudder inputs during certain stages of flight can cause catastrophic failure of an airplane’s vertical stabilizer," said Marion Blakey, chairwoman for the NTSB. "We have seen several circumstances that make it very apparent that this is something that is not widely known by the industry and in the pilot community."
A spokesperson for the agency says that it found during its investigation of the flight 587 crash that even a slight pressure on the rudder pedal, just a 1.5 inch tap, at high speeds could move the rudder much more than expected.
"The rudder movement in one direction and then back in the other direction could put more stress on the tail than it is built to bear," the spokesman says.
Flight 587’s Airbus A300 became uncontrollable after the tail fin sheared off over Jamaica Bay. The plane had reportedly been experiencing turbulence caused by a larger jet that had taken off from JFK Airport just previous to the Airbus.
"Before the separation of the vertical stabilizer and rudder, flight 587 twice experienced turbulence consistent with encountering wake vortices from a Boeing 747 that departed JFK ahead of the accident aircraft," Blakey says. The two airplanes were separated by about five miles and 90 seconds at the time of the vortex encounters."
Flight recorder data shows that the rudder on the doomed plane moved to its maximum limits left and right at least five times within seven seconds, according to Blakey. She says that the tail broke off at an altitude of 2,400 feet and a speed of 255 knots.
While admitting that such movement was "unusual," she refused to speculate on whether the rudder moved on its own, malfunctioned because of a mechanical problem or whether it was controlled by the pilot.
"We don’t know if this has any pertinence to the accident," a spokesperson said, but it is theoretically possible that over-compensation could cause the tail fin to fail or to fall off."
Aviation Week and Space Technology, a leading industry trade magazine, reported that it had done an independent and detailed analysis of the data and concluded that the rudder movements of flight 587, recorded in its last moments of flight, would cause forces on the side of the tail greater than it was designed to bear.
The NTSB says that further updates on the investigation into flight 587 will be forthcoming at regular intervals, but that it would be perhaps another year before the case report is released to the public.