Delta Airlines Flight 1972

The airplane landed with the right main landing gear partially extended. This was the second leg of the day in the airplane for this crew; the second officer (SO) completed walk around inspections prior to both flights and noted no discrepancies. The captain was hand flying the airplane in the initial takeoff climb, and selected landing gear up passing through 300 to 500 feet above ground level (agl). The red "doors" light illuminated on the front panel and the amber right main gear door light illuminated on the second officer's panel. All attempts to lower the right main gear were unsuccessful, so the captain elected to return to the airport and land with the right main gear extended about 15 degrees. Inspection of the right main landing gear revealed that the safety bar bent down about 20 degrees at the leading edge and 15 degrees at its midpoint. The safety bar's inboard flanges buckled just below the reinforced area. The inner gear door drive rod bent aft about 15 degrees at the upper attachment fitting, and the tube buckled and separated below the four attachment nuts. The outboard section of the clamshell gear door sustained mechanical damage. Examination of the airplane revealed that the door rods were not loose, and all were in good condition. A general inspection of the wheel well revealed no other damage. There was no abnormal wear or movement marks on the up-lock hook, and the hook was properly adjusted. The actuator adjustor plate was properly installed. Delta maintenance technicians installed new clamshell door halves and a new drive rod. They serviced the strut, isolated the right main clamshell gear door, and cycled the gear. Then they cycled the right main wheel with the door. Finally, they cycled all of the landing gear together. All wheels and doors cycled in proper sequence. Metallurgical examination discovered no cracks in the safety plate. There were no fatigue crack arrest marks or corrosion in the fracture faces on the drive rod; it fractured as a result of overstress. A black coating that felt greasy covered the interior side of the outer clamshell door. There was a rectangular scuffmark in the center of the black area, which had its long axis parallel to the longitudinal axis of the airplane. The black coating appeared pushed into a slight ridge along the outer edge of the scuffmark. A small piece of rubber was under a rivet in the middle of the scuffmark. After placing the tire and gear door together to match their positions when the airplane came to rest, the tire did not touch the scuffmark. Fourier Transform Infrared Spectroscopy (FTIR) examination of the small piece of rubber and samples from the tire and a chock determined that they were all hydrocarbon compounds, but could not distinguish between the samples. Whether the scuffmark and rubber piece came from runway debris or another rubber object could not be determined.

Verbatim NTSB analysis and probable cause from the NTSB dataset