Rockwell International 112 N12RX accident near Miami, Florida

Probable cause

Failure of the right main landing gear due to inadequate hydraulic pressure as result of a torn O-ring that was installed on the hydraulic pack’s check valve during overhaul.

NTSB analysis

When the pilot extended the landing gear in preparation for landing, she confirmed that all three green, gear-down indicator lights illuminated and felt the gear lock into place. However, upon touchdown, the right main landing gear collapsed, and the airplane veered off the runway and came to rest on the grass, resulting in substantial damage to the right wing. The nose and left main landing gear remained extended. Airport surveillance video was consistent with the pilot’s account.

Examination of the airplane revealed hydraulic fluid was visible down the belly of the airplane and the hydraulic reservoir was nearly empty. The airplane was placed on jacks and hydraulic fluid was added to the system. The gear was tested and functioned normally through its full extension and retraction cycle, but hydraulic fluid was observed leaking from the landing gear system’s hydraulic power pack. A review of maintenance records revealed the hydraulic power pack had been recently overhauled and was installed on the airplane about 1.8 hours before the accident.

Testing of the power pack revealed it functioned normally when the gear was extended; however, it would not hold pressure when the gear was retracted due to a leak at the check valve on the return port for the gear-downside of the pack. The check valve was removed, and two tears were observed on the valve’s O-ring. According to the company that had recently overhauled the pack, it’s not uncommon to see a tear/rupture on the O-ring after a gear collapse due to the back pressure of fluid that gets forced into the check valve. Visual examination of the tears revealed that the larger tear was in the direction of fluid flow when the gear collapsed. The other smaller tear was in the middle of the O-ring and it could not be determined if the tear was from the gear collapse. Since no other leaks or mechanical anomalies were observed in the postaccident examination of the landing gear system, this second smaller tear most likely occurred during the overhaul and resulted in a slow leak of hydraulic fluid and the subsequent loss of hydraulic pressure needed to fully extend the right main landing gear.

Though the pilot reported observing the gear-down indicator lights before landing, the gear-down microswitch may have been loose or improperly timed, providing a false gear-down “safe” indication before the gear was actually down and locked.

Text from the NTSB. Open the NTSB docket for ERA23LA202 for the full record.