NTSB Identification: CHI06FA158.
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Scheduled 14 CFR American Airlines
Accident occurred Tuesday, June 20, 2006 in Chicago, IL
Probable Cause Approval Date: 11/29/2007
Aircraft: McDonnell Douglas DC-9-83, registration: N961TW
Injuries: 136 Uninjured.
NTSB investigators either traveled in support of this investigation or conducted a significant amount of investigative work without any travel, and used data obtained from various sources to prepare this aircraft accident report.
The airplane was damaged during landing with the nose landing gear in the up position. According to statements from the flight crew and communications transcripts, the flight crew attempted to lower the landing gear and did not receive a gear down indication for the nose landing gear. The flight crew requested and performed a low-approach at which time the air traffic control tower personnel confirmed that the nose landing gear was not extended. The flight crew executed a climb to 6,000 feet and contacted American Airlines maintenance in an attempt to troubleshoot the problem. After performing the steps in the appropriate emergency checklists, including an attempted manual extension of the nose landing gear, proved unsuccessful, the flight crew executed a landing on runway 14R with the main landing gear extended and the nose landing gear in the up position. Examination of the airplane revealed that the nose landing gear spray deflector center link had fractured and the right hand urethane deflector was displaced. The deflector was rotated aft and was not in the track within the wheel well that contains the deflector when in the retracted position. When attempting to lower the nose landing gear, the deflector was observed to impinge on the nose landing gear wheel well structure preventing the nose landing gear from extending. The nose landing gear spray deflector components were sent to the NTSB Materials Laboratory for examination. The center deflector assembly was fractured along three separate lines where the right side deflector is attached. The aft right side of the center deflector was fractured through the bolt holes and the vertical and horizontal plate members. Magnified optical examinations of the three fracture faces revealed rough, crystalline matte gray surfaces consistent with overstress separations in cast aluminum alloys at each location. No evidence of porosity, corrosion or preexisting cracking was noted on any of the fracture faces. The engineering drawing specified the center deflector, p/n 5952241, as cast aluminum alloy C355 per federal specification QQ-A-596, solution heat treated and aged to T61 temper. A Brinell hardness impression on a piece of the center deflector measured 101 HB, which was consistent with the specified alloy and heat treatment.
The National Transportation Safety Board determines the probable cause(s) of this accident to be: The jammed nose landing gear due to a failure of the nose landing gear spray deflector for undetermined reasons. Full narrative available
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