19990909029049I

(.19) On September 9, 1999, at about 1138 central daylight time, a Douglas DC-9-31, N993Z, twa flight 600, registered to first security bank, north American trustee, operated as a 14 CFR part 121 domestic passenger flight, experienced a separation of the left main landing gear on landing rollout at Nashville International Airport, Nashville, Tennessee. Visual meteorological conditions prevailed and an IFR flight plan was filed. The airplane sustained minor damaged. The airline transport rated pilot-in-command (PIC), first officer (fo), 3 flight attendants and 38 passengers reported no injuries. Three passengers were transported and released from a local area hospital with minor injuries. The flight originated from st. louis, Missouri, 54 minutes before the incident. The fo stated he was flying the airplane and was vectored to the downwind and cleared for a visual approach to runway 02 left. He turned final and his sink rate was between 600 to 800 feet. The airplane touched down hard on the right main landing gear which surprised him and the PIC. The PIC immediately got on the flight controls with him as the airplane bounced. He asked the PIC if they were going to land or make a go-around. He received no response and continued with the landing. On the second impact he felt a vibration, and it became evident that they had a directional control problem. He initially thought they had a landing gear strut or tire failure. The left wing started to settle and made contact with the ground. The PIC informed the tower to roll the equipment, and pulled the left start fuel lever to the off position. He pulled the right start fuel lever to the off position, and the airplane came to a stop. The crash rescue fire (crf) vehicles arrived, and the PIC communicated with them and the tower. They completed the evacuation checklist, and briefed the flight attendants and passengers. After some communication with the crf personnel an evacuation was made down the evacuation emergency slide at the L-1 door. The PIC stated right before touchdown, he knew the fo was not going to make a good landing. The airplane touched down hard, but he did not expect a hard landing of that magnitude. He immediately got on the flight controls and remained on the flight controls until the airplane came to a stop. On the second touchdown, he felt a wobble on the left side. The airplane started a left roll, and he experienced directional control problems. He used right brake to keep the airplane on centerline. As soon as the airplane stopped, he started coordinating with crf and tower personnel. The crf arrived without delay. They ran the evacuation checklist, and he briefed the flight attendants and passengers. A short time later after coordination with the crf personnel, he commanded an evacuation out the L-1 door. All flight attendants stated the airplane experienced a hard landing. All personnel completed an emergency evacuation out the L-1 door in an orderly fashion. No problems were encountered with the emergency equipment. Review of recorded transmissions between twa 600 and Nashville tower local control, revealed that twa 600 was cleared to land at 1135. At 1138, northwest airlines flight 1746 informed the tower that twa had just lost its gear. (.4)the first officer failed to maintain the proper rate of descent (sink rate) resulting in a hard landing on touch down, and separation of the left main landing gear during landing rollout. The pilot-in-command stated he knew the first officer was not going to make a good landing. He did not take any corrective action other than informing the first officer initially to increase power. Examination of the left main landing gear assembly revealed a preexisting crack in the outer cylinder housing.