Cessna 560XL N503UP incident near San Jose, California

Probable cause

The mechanic’s incorrect installation of the right main landing gear (MLG) aft trunnion pivot pin, which resulted in the pin separating from the trunnion, the trunnion puncturing the right wing, and the right MLG collapsing.

NTSB analysis

The pilot and copilot reported that, during the landing roll, the airplane bounced and then veered right and that the pilot then corrected back to the runway centerline. The copilot added that the airplane’s right side seemed to “dip” as it continued to pull right, and the pilot added that the airplane’s right side was lower than its left side, so they assumed that the right main landing gear (MLG) had a flat tire. Subsequently, the pilot was able to taxi the airplane off the runway and park it on a taxiway, and the passengers disembarked without incident.

Examination of the airplane revealed that the aft portion of the right MLG trunnion was protruding through the top of the right wing and that the MLG strut and wheel were positioned out and aft in about a 45° angle from their original position. The right MLG trunnion aft pivot pin was not in the trunnion but remained in the trunnion mount in the aft wing spar; it was easily removed from the mount by hand. The retaining bolt used to keep the pivot pin in the trunnion was in place and secured with a nut and cotter pin.

Review of the airplane’s maintenance records revealed that the left and right MLG trunnions had been replaced with new trunnions and trunnion pivot pins 8 days before the incident. The mechanic who performed the work stated that, after installing the right MLG aft trunnion pivot pin, it must have shifted aft when he went to install the bolt through the pin. He stated that an “air-pocket” must have developed and pushed the pin back out. He added that the pin looked fully engaged and that he noted no faults during postmaintenance operational checks. Therefore, based on the evidence, it is likely that, after the mechanic installed the right MLG aft trunnion pivot pin, it backed out, which led to the retaining bolt not being installed in the hole in the pivot pin and resulted in the pin separating from the trunnion, the trunnion puncturing the right wing, and the right MLG collapsing.

Following the incident, the airplane manufacturer revised the trunnion pivot pin installation procedures in the Airplane Maintenance Manual. The revision included, in part, a step for maintenance personnel to visually check and ensure that the bolt is visible when looking through the pivot pin from the aft side and that, if it is not visible, to remove it, ensure that the pivot pin is fully installed in the trunnion assembly, and reinstall the bolt.

Text from the NTSB. Open the NTSB docket for WPR17IA189 for the full record.