WPR20LA290

The pilots were performing an instructional flight and completed a normal approach to the destination runway. The main landing gear touched down on the runway surface first and as soon as the nose lowered, the nose landing gear collapsed. The nose landing gear fork assembly had collapsed when a pivot-axle welded to the arm in the nose landing gear welding assembly fractured. A metallurgical examination revealed the pivot-axle fracture surface exhibited two opposite facing fatigue cracks propagating inward on the pivot-axle due to reverse bending, consistent with repeated landing forces and cycles prior to the accident. The cracks propagated until the remaining pivot-axle cross section could not withstand the loads on the last landing cycle and succumbed to fracture from overstress. The location of the crack’s origins required disassembly to detect. Therefore, it would not have been easily detected during routine maintenance. Following this accident, the manufacturer issued a mandatory service bulletin to routinely inspect the nose landing gear for cracks using dye penetrant.

On August 19, 2020, about 2150 mountain standard time, a Diamond DA-40 airplane, N386MA, sustained substantial damage when it was involved in an accident in Benson, Arizona. The flight instructor and pilot under instruction (PUI) were not injured. The airplane was operated as a Title 14 Code of Federal Regulations Part 91 instructional flight. The flight instructor stated that they departed from Tucson, Arizona with the purpose of landing in Benson for the PUI to fulfill a night cross-country flight time requirement toward his commercial license. The PUI completed a normal approach to runway 10 and started the landing flare at about 65 knots. The main landing gear touched down on the runway surface first and as soon as the nose lowered, they heard a loud noise. The PUI held the control stick aft in an attempt to keep the nose up as the airspeed was slowing, but they soon heard the strut scraping along the runway. Upon egressing the airplane, they observed that the nose gear had separated at the pivot axle (see figure 1). Figure 1: Nose Landing Gear Nose Landing Gear The nose landing gear, part number D41-3223-10-00_1, was installed at an unknown time, but sometime before the operator purchased the airplane in 2014 at a total time of 1427.7 hours. The airframe had a total time of 8,528.3 hours. The nose landing gear fork assembly collapsed upon landing when a pivot-axle welded to the arm in the nose landing gear assembly fractured. A metallurgical examination revealed the pivot-axle fracture surface exhibited two opposite facing cracks propagating inward on the pivot axle. The pivot-axle fracture surfaces were consistent with fatigue, due to reverse bending from landing forces and cycles. The cracks propagated until the remaining pivot-axle cross section could not withstand the loads on the last landing cycle and succumbed to fracture from overstress. With the pivot axle having separated, the adjacent nose landing gear components would be subject to fracture from overstress. Examination of crack’s origins revealed that they could be detected with nondestructive inspection techniques, such as fluorescent penetrant inspection (FPI) or magnetic particle inspection (MPI). Both these techniques, as well as certain ultrasonic inspection kits, could be employed to look for similar cracks in other welded assemblies, but would require disassembly to access. Diamond Aircraft stated that they are aware of nine other cases of cracking on this part with off of the airplanes having about 5,000 hours of total time. Following this accident, Diamond Aircraft issued a Mandatory Service Bulletin (MSB) 40-091 that stated, in part: For airplanes equipped with the D41-3223-10-00_1 nose landing gear leg, and with a TTAF [total time airframe] of 3000 hours or greater, within the next 25 hours of operation if operated on unprepared surfaces, or within the next 100 hours of operation if operated on paved surfaces. [Dye penetrant] Inspection must be repeated every 100hours thereafter. The terminating action of this service bulletin is the installation of a D41-3223-10-00_2 or later nose landing gear leg.