HISTORY OF FLIGHT On June 20, 2006, about 0630 central daylight time, a McDonnell Douglas DC-9-83, N961TW, piloted by an airline transport pilot, sustained substantial damage during a nose-wheel up landing on runway 14R (13,000 feet by 200 feet, asphalt/concrete), at the O'Hare International Airport (ORD), Chicago, Illinois. The 14 CFR Part 121 domestic passenger flight was being operated by American Airlines as flight 1740. There were no injuries to the 131 passenger and 5 crewmembers. The flight originated from the Los Angeles International Airport (LAX), Los Angeles, California, about 2350 pacific daylight time. 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. PERSONNEL INFORMATION The captain held an airline transport pilot certificate with a multi-engine airplane rating. The certificate listed a type rating for DC-9 airplanes. The certificate also listed commercial pilot privileges for single engine airplanes. The captain's most recent fist class medical certificate was issued on April 12, 2006. The first officer held an airline transport pilot certificate with single and multi-engine airplane ratings. The certificate listed a type rating for second in command privileges in DC-9 airplanes. The first officer's most recent second class medical certificate was issued on December 18, 2005. AIRCRAFT INFORMATION The airplane was a McDonnell Douglas DC-9-83 transport category airplane. Two Pratt and Whitney JT8D series engines producing 20,850 pounds of thrust each powered the airplane. The airplane was configured to seat 136 occupants including 131 passengers, 3 cabin crewmembers and 2 flight crewmembers. The airplane had a retractable tricycle landing gear configuration. METEOROLOGICAL INFORMATION The reported weather conditions at ORD at 0553 were: Winds variable at 4 knots; Visibility 10 statute miles; Scattered clouds at 25,000 feet; Temperature 18 degrees C.; Dew point 14 degrees C.; Altimeter setting 30.03 inches of Mercury. WRECKAGE AND IMPACT INFORMATION 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. TESTS AND RESEARCH 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. During the investigation it was discovered that another DC-9 type airplane had arrived at ORD with a broken spray deflector. This airplane's landing gear did extend and the airplane made an uneventful landing. The spray deflector from this airplane had fractures in the same general location as those of the accident airplane's deflector. During the investigation, it was found that airline personnel have access to and use a type of towbarless tug on various aircraft. Tests by the airline confirmed that the tug can apply an upward force to the spray deflector of DC-9 type airplanes. No determination could be made as to whether either the accident airplane or the other DC-9 with the broken spray deflector had been moved using one of the towbarless tugs during the preceding several days. ADDITIONAL INFORMATION The Federal Aviation Administration, Boeing, American Airlines, and the Allied Pilots Association were parties to the investigation.