Bombardier CL 600 2C10 N157GJ

The flight crew had flown the incident airplane on the day before the incident and heard a sound, which the captain described as a “bang,” when extending the landing gear on approach. The first officer inspected the nose gear after landing and indicated that it looked like the data plate had come loose on the strut. The captain sent photographs of the nose landing gear to company maintenance control and then entered “placard strap bent” in the airplane logbook. He did not write up the “bang” sound because of his conversation with maintenance control. Maintenance personnel repaired the damaged placard that night but did not do any additional inspections. If the captain had been more descriptive in his writeup, additional maintenance would likely have been completed that may have found the mechanical failure in nose gear system. During the incident flight, the crew observed a GEAR DISAGREE caution message during their approach and conducted a go-around to troubleshoot the problem. The first officer, as pilot monitoring, began performing the GEAR DISAGREE checklist, however, he misstated several items in the checklist and did not perform the last item that directed him to perform another checklist. Although operational issues were identified during this investigation related to checklist usage and company procedures, they did not relate or contribute to the cause of the incident. The flight was subsequently cleared to land, and the airplane touched down without the nose gear extended, which resulted in minor damage to the forward fuselage. Nose Landing Gear Failure The opening and closing of the landing gear doors were accomplished through the driven link, lower link, and upper link assemblies, articulated by the drive link assembly attached to the drive arm assembly. Postincident examination of the nose landing gear revealed that two areas on the lower link assembly had damage from contacting the upper link assembly and the drive link assembly. The spherical bearing attached to the drive link assembly had fractured away from the lower link assembly. The drive arm assembly that attached to the lower lock link assembly using two D head pin/nut combinations had only one pin/nut still attached; the bolt and washer were heavily distorted. The portion of the hole in the lower lock link assembly that facilitated one of the two bolts/nuts to fasten the drive arm assembly was found sheared from the lug. Examination of the primed mating surfaces of the drive arm assembly and lower lock link assembly revealed missing paint adjacent to the bolt holes, indicating back-and-forth movement between the two components. Given that the end of the protruding threads on the sheared pin did not show any physical damage from the threads interacting with the nut, it is likely that one of the two nuts on the lower D head pins securing and providing anti-rotation between the drive arm assembly to the lower lock link assembly lost preload and backed off. With the nut missing from the D head pin, the drive arm assembly was allowed to have side-to-side rotational movement as well as a gap with the lower lock link assembly during the extension and retraction of the gear. Given the absence of the nut and the resulting gap between components, loads were transferred to the upper D head pin, which caused the aluminum lug to fail in tensile overload.  With the upper D head pin no longer attached, the entire load was transferred through the lower D head pin, and the subsequent loads applied resulted in fracture of the lower pin in shear. Because the drive arm was no longer tethered to the lock link, the drive arm was free to rotate, and, thus, the door links were able to go over center, farther than designed, allowing the drive rod to contact the lower link. When the nose landing gear was commanded to extend, the drive link could not pull the upper/lower link out of lock and, thus, as the nose landing gear continued to traverse, the rod end of the driven link contacted the lower link and subsequently failed in bending. As a result, the door linkage was no longer connected to the kinematics of the landing gear; the air loads on the forward doors held the upper and lower linkage in the over center condition, and the nose landing gear subsequently rested on the forward doors. Thus, the nose landing gear failed to fully extend when the lower link, upper link, and driven link assemblies articulated over center, mechanically immobilizing those components and the attached door rods, preventing them from fully extending. The over centering of the linkage occurred due to the overtravel of the drive link assembly, which was the result of missing and damaged fastening hardware on the drive arm assembly. After the incident, GoJet Airlines inspected its fleet of 47 CRJ 700 airplanes to ensure that the nose landing gear drive arm attaching hardware was intact. As a result of the detailed inspection, three airplanes were found with loose hardware, which was replaced in accordance with the applicable maintenance manual. In addition, Goodrich published a Service Bulletin that directed operators to remove the drive arm pin nuts, replace them with nuts with a new part number, and install them with Loctite at a higher torque value. Bombardier also published a Service Bulletin, which recommended operators accomplish the Goodrich Service Bulletin within 1,320 flight hours from the bulletin release date.

Quoted verbatim from the NTSB record.