SEVENTH UPDATE ON NTSB INVESTIGATION INTO CRASH OF

AMERICAN AIRLINES FLIGHT 587

 

The Relevance of the SIA A300 Incident

This snippet below, (from the recent NTSB 7th update) would seem to revisit my theory of a pressure-wave reverberation induced within the Central Air Data Computer by aberrant pitot-static measured pressure inputs. Whether by water in the system or otherwise-induced pressure fluctuations, in my opinion it remains a mechanism by which a chaotic flutter mode could be introduced into the rudder circuit via the rudder limiter or yaw damper.

This SIA incident (below) could just as likely have been caused by water in the static system. The tricky woo aspect of water in the static system is that normal post-incident trouble-shooting can eliminate it, without its presence (and therefore significance) ever being noted (or suspected). It is then perhaps wishful thinking to cinch up some pneumatic connections a little tighter and then put it all down to having been an air-leak.

I see this incident as a significant development in the sleuthing of AA587's initiating events.

Other Airbus Event

The Safety Board is interested in another upset event last year involving an Airbus aircraft. On November 25, 2001, a Singapore Airlines A340-300 departed Singapore for a scheduled flight to Dhaka, with 96 persons aboard. Shortly after takeoff, the pilots noticed a problem with airspeed indicators. Among other things, there were overspeed warnings and large rudder movements without pilot input. The aircraft returned to Singapore and made a safe landing; there were no injuries.

Inspection subsequently found problems with the pitot and static connections to the air data computers, which may have been introduced during recent maintenance. The Civil Aviation Authority of Singapore is investigating the incident. Due to computed loads that might have been experienced by the vertical stabilizer, it and the attached rudder were removed from the aircraft shortly after the incident and were recently examined in Germany. Although no damage was found in either the stabilizer or the rudder, the Board is interested in the rudder system's role in this event.



http://www.pprune.org/forums/showth...87&pagenumber=2

Links to Other Pprune posts about AA587

NTSB Advisory

National Transportation Safety Board

Washington, DC 20594

April 12, 2002

The National Transportation Safety Board today released the following updated information on its investigation of the November 12, 2001, crash of American Airlines flight 587, an Airbus A300-600, in Belle Harbor, New York, which resulted in the deaths of all 260 persons aboard and 5 persons on the ground.

Vertical Stabilizer and Rudder

Work is continuing at NASA's Langley Research Center in Hampton, Virginia on the composite vertical stabilizer and rudder that separated from the aircraft. The non-destructive testing at NASA (tap test, photography, Lamb wave test, thermography and ultrasound mapping) is essentially complete. Destructive testing has begun and will take at least four to five months to complete. Scanning electron microscope (SEM) examination of the six fractured aft rudder fitting attachment bolts has also been accomplished.

The exemplar rudder that was purchased by the Board has undergone non-destructive testing at the Sandia National Laboratory in New Mexico and will be delivered to the investigative team at NASA Langley. The stabilizer and rudder from American Airlines flight 903 (please see Fifth and Sixth Updates for details) are available for further examination by the Board if circumstances warrant. If needed, another vertical stabilizer has been identified for the Board's purchase.

The three rudder power control units (PCUs, also called actuators) from Flight 587 have been examined by CT-Scan at the U.S. Army's Aberdeen Proving Ground in Maryland. They were subsequently bench tested and torn down at the manufacturer (TRW) in France. Tests so far have revealed no pre-existing problems with the PCUs.

Aircraft Performance

The Safety Board has asked NASA to produce a model of the wake vortices that flight 587 encountered to further study their possible role in the sequence of events.

The members of the Aircraft Performance group have defined the parameters of the filtering process on the flight data recorder (FDR), which has allowed them to define more accurately the rudder movements in the last moments of the flight  (the rudder movements described in the Board's recommendation letter of February 8 are further confirmed by the latest calculations). With the refined rudder data, work is proceeding on calculating the lateral loads encountered by the flight crew at the front of the aircraft. The human performance and operations groups will attempt to determine how those loads possibly affected pilot actions. The loads at the crew stations may be higher than recorded by the FDR, which measures loads in the center of the aircraft.

In addition, the Board will be able to refine air loads and structural loads introduced on the fin caused by rudder deflections and side-slip angles.

Airbus has upgraded its Finite Element Model, which is a structural loads analysis tool that allows investigators to assess loads on small sections of the stabilizer/rudder assembly. Detailed load analyses can be performed on small critical subsections of the stabilizer/rudder assembly. This will enable investigators to examine a number of loading scenarios.

Other Airbus Event

The Safety Board is interested in another upset event last year involving an Airbus aircraft. On November 25, 2001, a Singapore Airlines A340-300 departed Singapore for a scheduled flight to Dhaka, with 96 persons aboard. Shortly after takeoff, the pilots noticed a problem with airspeed indicators. Among other things, there were overspeed warnings and large rudder movements without pilot input. The aircraft returned to Singapore and made a safe landing; there were no injuries.

Inspection subsequently found problems with the pitot and static connections to the air data computers, which may have been introduced during recent maintenance. The Civil Aviation Authority of Singapore is investigating the incident. Due to computed loads that might have been experienced by the vertical stabilizer, it and the attached rudder were removed from the aircraft shortly after the incident and were recently examined in Germany. Although no damage was found in either the stabilizer or the rudder, the Board is interested in the rudder system's role in this event.

In addition, the FAA and Airbus identified seven Airbus A300-600 and A310 aircraft whose vertical stabilizers needed to be ultrasonically inspected because of possible high lateral loads experienced by those aircraft. Three of the aircraft were from American Airlines, and the other four were from FedEx, Tarom and Interflug (two European carriers), and the German air force. The FAA reports that all seven have been checked and only one exhibited any damage to the vertical stabilizer. That was the previously reported American Airlines flight 903 aircraft that experienced an upset event in 1997.

Toxicological Tests

No blood or urine was available for testing from the pilots of flight 587, but tissue samples were obtained for routine toxicological evaluation on the captain and the first officer. Ethanol and other volatiles (acetaldehyde and n-propanol) were detected in small amounts in the captain's specimens. Such findings are commonly associated with the post-mortem production of ethanol.

Ephedrine and pseudoephedrine were detected in the first officer's specimens. These substances are present in many over-the-counter medications used for the treatment of upper respiratory symptoms, and are commonly found in nutritional supplements marketed for a variety of purposes. They are both mild stimulants.

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