N376MQ
Short Brothers SD3-60
The right main landing gear collapsed on landing rollout. Initial examination of the airplane by the FAA revealed the right main landing gear shock absorber had failed. Examination of the components by the NTSB laboratory revealed the manufacturer had not applied sealant on the internal surface of the cylinder nut in the radius area between the threads and the flange before the nut was assembled. This resulted in stress corrosion cracking of the cylinder nut, and subsequent collapse of the right main landing gear.
On February 18, 1995, about 1606 Atlantic standard time, a Short SD3-60, N376MQ, registered to Security Pacific Esquire, operating as a 14 CFR Part 121 scheduled domestic passenger flight, by Executive Airlines Inc., San Juan, Puerto Rico, doing business as American Eagle flight 514, experienced a collapse of the right main landing gear on landing rollout at Cyril E. King Airport, St. Thomas, U.S. Virgin Islands. Visual meteorological conditions prevailed and an IFR flight plan was filed. The airplane sustained minor damage. The airline transport pilot-in-command, airline transport pilot first officer, 1 flight attendant, and 33 passengers were not injured. The flight originated from the Luis Munoz Marin International Airport, San Juan, Puerto Rico, about 51 minutes before the incident. The pilot-in-command stated the landing gear was lowered and the right main gear landing light did not illuminate. The control tower was notified of the malfunction, and a low pass was requested and made so the tower could observe the position of the landing gear. He was informed by the tower that the landing gear appeared to be down. The emergency procedures were completed, and the airplane was landed on the left main landing gear. As the airspeed decreased the right main landing gear touched down on the runway and collapsed. Initial on-scene examination of the airplane by the FAA revealed a failure of the right main landing gear shock absorber. The components were forwarded to the NTSB Materials Laboratory Division for analysis. Examination of the right main landing gear shock absorber revealed fractures in the gland housing and the cylinder nut. Optical examination of the gland housing fractures revealed features typical of overstress separations along the transverse grain flow in the aluminum alloys. No evidence of preexisting cracking was observed on the fractures. The cylinder nut fracture had a woody fracture topography showing little or no bulk deformation or yielding and faint crack arrest marks indicating the crack had grown progressively from multiple locations of the inside surface of the nut flange. High magnification examination established the fracture was intergranular and followed the grain boundaries through the thickness of the flange, consistent with stress corrosion cracking. Assembly drawings for the shock absorber indicate that two beads of sealant material are applied in the area of the cylinder nut. One bead is applied on the internal surface of the nut in the radius area between the threads and the flange. Another bead of sealant is applied around the top of the nut. Examination of the nut revealed sealant was applied between the top of the nut and outer diameter of the cylinder. No sealant was found inside the nut. (For additional information see, NTSB Metallurgist's Factual Report No. 95-96). The right main landing gear shock absorber was released to Executive Airlines Inc., on May 9, 1995.
Inadequate application of sealant on the right main landing gear shock absorber cylinder nut, and inadequate quality control by the manufacturer.
Source: NTSB Aviation Accident Database
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