Incorrectly sized parts found after Icelandair 757 gear collapses

Photo by Karam Sodhi | AeroNewsX

Icelandic investigation authorities have found incorrectly sized components on the landing gear assembly of an Icelandair Boeing 757-200 that suffered a landing gear collapse at Reykjavik Airport earlier this year. Icelandair Flight 529, operated by aircraft TF-FIA, a Boeing 757-200, flew from Berlin Tegel to Iceland's Reykjavik Airport. According to investigation reports, the aircraft touched down on its right main landing gear followed by its left main landing gear. Immediately, abnormal metal fracturing sounds alarmed passengers, and the right side of the airplane sunk soon after. The right engine hit the runway as the flight ground to a halt. On-site examination of the 757 showed that the sided strut detached from the shock strut, the swivel nut. The washer spline was missing from the immediate scene, later found near the aircraft touchdown point. Finally, the locking bolt for the swivel nut was sheered off. The Rannsóknarnefnd Samgönguslysa (RNSA) report states that the swivel threads underwent shrinking twice during overhaul works in December 2008 and November 2019. In 2018, the swivel threads shrunk 1 /16 inch and in November 2018, the swivel threads shrunk again by another 1/16 inch, bringing the swivel thread 1/8 inch undersize. The reduction of the size of the swivel nuts was permitted as per the Boeing repair manual but required a special nut to be manufactured. However, investigators, later on, revealed that the nut from the landing gear was too big for the undersized swivel threads. The RNSA report states "For 1/8 inch downsize, the Minor Diameter of the NUT was required to be in the range of 1.5439 to 1.5539 inch. Initial measurements by the ITSB after the accident has shown the Minor Diameter of the nut threads to be 1.617 inches. The preliminary investigation, therefore, indicates the nut to be too large for the 1/8 inch undersized swivel threads." Investigations have not happened due to the COVID-19 travel ban to the United States, but the ITSB did issue the interim safety recommendations to Icelandair and Cabo Verde Airlines. Four Boeing 757-200 registered as TF-ISS, TF0FIA, TF0ISY, and D4-CCG received overhaul landing gears from Landing Gears Technologies, and these aircraft have to be inspected.

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