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Posted on 11/24/2001 8:21:02 AM PST by eno_

FAA-mandated inspections of Airbus A300-600 series and A310 aircraft with composite vertical stabilizers were underway last week while American Airlines Flight 587 accident investigators eyed rudder deflection as another contributing factor in the Nov. 12 crash.

View of rear fuselage looking aft shows left center fin lug in left foreground with repair rivets visible. The fuselage clevis for the left aft lug is partly visible in the center, obscured by a torn piece of fairing. Part of the delaminated stabilizer skin rises above the fairing like a shark fin. Wake turbulence and composite structure of the vertical stabilizer were identified as possible accident components by the National Transportation Safety Board in the first few days of its probe (AW&ST Nov. 19, p. 32).

Japan Airlines Flight 47, a Boeing 747-400, began its takeoff roll on Runway 31L at New York JFK International Airport at 9:13 a.m. Flight 587, en route to Santo Domingo, Dominican Republic, followed 1 min. 45 sec. later. Winds were from the northwest and Flight 587's flight path was about 800 ft. below and 0.7 naut. mi. east of Flight 47's at time of the aircraft's last transponder return.

According to the NTSB, flight data recorder (FDR) information indicates that Flight 587 encountered two wake vortices generated byFlight 47. Each is followed by "rattling" noises heard on preliminary cockpit voice recorder readouts at 66 sec. and 80 sec. after liftoff of Flight 587(see timeline).

The first rattling noise was followed by the captain's report of "wake encounter"; the second, by loss of control of the aircraft. Both encounters averaged about 0.1g lateral movement, according to the safety board.

The NTSB last week said the cockpit voice recorder (CVR) runs 154 sec. following start of takeoff roll, 10 sec. longer than previously indicated in preliminary accident data. The safety board calculates 93 sec. elapsed from Flight 587's liftoff to end of FDR data.

In the final 8 sec. of FDR data, Flight 587 experienced three strong lateral movements, two to the right, of 0.3 and 0.4g, followed by one to the left of 0.3g, which coincided with rudder movements, according to the NTSB. Rudder data from the FDR is unreliable about 2.5 sec. before the end of the recording.

During this lateral g sequence the sideslip angle reached 8 deg., followed by full motion of the rudder in the opposite direction, according to a source close to the investigation. The FDR's rudder pedal traces matched the rudder position itself, but this does not necessarily mean the pilot commanded the rudder because the pedals are probably backdriven by the control cables. Extreme control application is sometimes a sign of pilot-induced oscillation (PIO), but there is no clear public evidence of that yet. PIOs usually involve a pilot executing a precise tracking task, in an aircraft with a certain response lag, and with the pilot in a panicked state. They are often triggered by responding to a change in flight path or handling.

Flight 587's vertical stabilizer departed the aircraft first, with the rudder and tail fin found floating 200 yd. apart in Jamaica Bay. The engines and main wreckage plunged about 0.6 naut. mi. south, into the Rockaways beachfront community of Belle Harbor, killing all 260 on board and five people on the ground about 103 sec. after the aircraft's departure from JFK.

The NTSB is continuing to look for the cause of the rudder deflections. Last week, the board clarified that further examination of the jackscrew and FDR data show the trim setting to have been close to neutral--not 10 deg. left as initially reported.

UPDATED INVESTIGATION data released last week by the NTSB highlighted a May 11, 1999, rudder movement incident involving another American Airlines A300-600, tail No. N7082A. The aircraft, with 119 passengers and 10 crew on board, experienced multiple rudder deflections while on approach to Runway 9R at Miami, and landed safely. FDR data indicated the rudder deviated continuously between 5-11 deg. each side of center. That investigation indicated maintenance personnel at Tulsa, Okla., had cross-connected the wiring of the autopilot. The FAA and its French counterpart issued Airworthiness Directives (ADs) following an Airbus advisory to check for cross-connects. N7082A was repaired, as was another aircraft found to have been cross-wired.

In 1996, an A300 began to shake violently after climbing to 31,000 ft., with a 5-6 Hz. rudder pedal movement that could not be overridden, according to NASA's Aviation Safety Reporting System. The crew took immediate action to control the aircraft; they slowed and started to descend. The pedals returned to normal upon slowing, but the crew declared an emergency and landed. They reported weather as clear and smooth.

Last week, the NTSB's Aircraft Performance Group chairman joined the BEA French accident investigation bureau members and Airbus engineers in Toulouse to further extract flight profile and performance data on the accident aircraft, although no details were available as to what specific tests would be performed.

Investigators also plan to look for signs of structural weaknesses in the aircraft that may have resulted from a clear air turbulence incident in November 1994. FAA incident data indicate there was "minor damage" to the aircraft, while last week's NTSB's investigation update says American reported no damage to the tail.

Tests to determine whether advanced composite materials played a role in the inflight failure of the tail assembly are ongoing, according to the NTSB.

Investigators completed visual examinations of the aircraft's tail fin and rudder assemblies in the first week following the accident. On Nov. 16, aircraft operators were asked to do the same, when the FAA issued an Emergency AD 2001-23-51. It ordered all operators of -600 series and A310 aircraft with Modification 4886 to conduct a one-time detailed visual examination of the vertical stabilizers made of advanced composite materials.

Operators are checking the vertical stabilizer-to-fuselage attachment fittings (including the main attachment lugs and transverse load fittings) as well as rudder-to-vertical stabilizer attachment fittings, including hinge arms as well as rudder hinge, support and rudder actuator support fittings.

The purpose of the AD is to detect signs of damage, alterations, repairs or areas of discrepancy. This would include pulled or loose fasteners, corrosion or distorted flanges in metallic areas and delamination, moisture damage and cracks, or abrading in paint surfaces in composite areas.

Operators have 15 days from receipt of the AD to submit their inspection reports.

The AD makes particular note of searching for repairs or alterations. The accident aircraft had a delamination of its left center fin attach lug repaired, which included a series of rivets visible in NTSB photos (http://www.ntsb.gov/Events/2001/ AA587/tailcomp.htm).

The directive is considered an interim action to assess a potentially unsafe condition and to determine whether additional action is necessary.

By the end of October, 242 -600s were in service with 27 operators, according to Airbus. American last week reported finding no problems following completion of its voluntary visual inspections of the 34 remaining -600s in its fleet. Federal Express expects to complete inspection of its 37 A300s within the specified time.

Aircraft wreckage is being temporarily stored at Floyd Bennett Field, located near JFK airport, while some components of the tail fin and rudder assembles will be transferred to another facility for more detailed examinations. The accident aircraft's two General Electric CF6-80C2 engines will undergo teardown at General Electric's Tulsa facility within a few weeks, according to the NTSB.

The board may issue safety recommendations at any time during the investigation, which the NTSB anticipates will continue for more than a year.

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