ERA23LA202

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pack revealed it functioned normally when the gear was extended; however, it would not hold pressure when the gear was retracted due to a leak at the check valve on the return port for the gear-downside of the pack.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.

On April 18, 2023, at 0913 eastern daylight time, a Rockwell International 112 airplane, N12RX, was substantially damaged when it was involved in an accident at the Miami Executive Airport (TMB), Miami, Florida. The commercial pilot was not injured. No flight plan was filed for the Title 14 Code of Federal Regulations Part 91 personal flight. This was the pilot’s first flight in the airplane after being checked out in it the week before. She reported completing three uneventful touch-and-go landings at the North Perry Airport (HWO), Hollywood, Florida, before she noticed that the transponder was not working. She made a full-stop landing and called the owner, who made an appointment to get the transponder fixed that day at an avionics shop located at Miami Executive Airport (TMB), Miami, Florida. Before departing for TMB, the pilot contacted air traffic control and received permission to make the short flight from HWO to TMB with no transponder. She said the short flight was normal and she was cleared to land straight-in on runway 9L. The pilot said she extended the landing gear and confirmed that all three gear-down indicator lights were illuminated and felt the gear lock into place. The pilot said that when the airplane touched down, it felt “unbalanced.” She could feel the nose gear and the left main gear on the ground, but the right main gear felt like it wasn’t fully extended. The airplane veered off the runway and came to rest on the grass, resulting in substantial damage to the right wing. The nose gear and left main gear remained extended. Hydraulic fluid was observed on the belly of the airplane and streaming back toward the tail. The pilot said she conducted a thorough preflight inspection of the airplane before the flight and did not see any hydraulic fluid on the exterior of the airplane. A review of airport surveillance video revealed the airplane’s landing gear appeared to be extended before landing. As soon as the airplane touched down, the right main landing gear collapsed. WRECKAGE EXAMINATION The airplane was recovered and placed on jacks at a maintenance facility at TMB. Only a small amount of hydraulic fluid was observed in the hydraulic reservoir. The landing gear was tested via manual use of the landing gear handle in the cockpit, but due to a lack of hydraulic pressure from the lack of fluid, the gear would not extend or retract. Hydraulic fluid was added to the system and the gear was tested again. This time, the gear functioned normally through its full extension and retraction cycle, and no mechanical anomalies were observed with the landing gear system. However, hydraulic fluid was observed leaking from the hydraulic power pack. No other leaks were observed. A review of airplane maintenance records revealed that the hydraulic power pack had been recently overhauled and was installed about 1.8 hours before the accident. The hydraulic power pack was shipped to the company that overhauled the unit, where it was tested andpartially disassembled under the supervision of the FAA. The results of the bench test revealed that the hydraulic power pack functioned normally when the gear was extended; however, it would not hold pressure when the gear was retracted. According to the overhaul company, this pressure loss was not uncommon. They said that when a gear collapses, a back pressure of fluid gets forced into the hydraulic pack’s check valve and tears or ruptures the check valve’s O-ring. The check valve was removed, and there was a large tear on the O-ring consistent in the direction of fluid flow from when the gear collapsed. However, there was another smaller tear in the middle of the O-ring. The overhaul company stated the tear could have been from fluid going either in or out of the valve. They did not determine the direction of the tear. The O-ring was examined under magnification by the NTSB, and the direction of the tear could not be determined. The hydraulic landing gear system is designed so when the pilot places the landing gear handle in the UP position, the hydraulic power pack is energized, and hydraulic fluid is directed to the up port of each gear actuating cylinder to retract the gear. The landing gear is held up by hydraulic pressure. If there is inadequate hydraulic pressure in the system due to a lack of hydraulic fluid the gear is unable to retract, and the pilot would feel the gear “bump” as it repeatedly tried to retract the gear. There would also be a spike on the amp meter and the hydraulic power pack circuit breaker would pop. The pilot reported that the landing retracted normally, and no gear abnormalities were observed. When the landing gear is selected to the DOWN position, the hydraulic power pack is energized, and hydraulic fluid is directed to the down port of each actuating cylinder to extend the gear. When all three gears are extended and locked, piston-operated switches on each actuating cylinder engage, and the hydraulic actuating switches de-energize the hydraulic pump. The pump shuts off and the sequence is complete. The gears are held in the down position by mechanical locks and not system pressure. There is also a gear-down lock microswitch that is energized during the gear extension sequence to illuminate the three gear-down indicator lights. This microswitch needs to be adjusted properly by a mechanic so it comes on when the gear is, in fact, fully extended. If not, the lights will illuminate before the gear is fully extended and give a false “safe” indication to the pilot. During the postaccident examination of the landing gear, the three gear-down indicator lights illuminated green when the gear was extended, indicating the gear was down and locked, and the three lights turned off when the gear was retracted. As such, no further testing of the microswitch timing was conducted or confirmed.