San Jose, CA, USA
N304LA
Piper PA46
Despite several attempts, the airplane’s landing gear was unable to be extended and locked during the approach to the destination airport. The flight instructor elected to divert to a more suitable airport where they could circle while they tried to extend the landing gear. Continued attempts by the pilot receiving instruction and the flight instructor to troubleshoot the problem and extend the landing gear were unsuccessful. The flight instructor subsequently landed the airplane with the landing gear retracted. Postaccident examination of the land gear system revealed that the hydraulic power pack used to operate the landing gear had a lack of adequate hydraulic fluid in the reservoir, consistent with a hydraulic line being disconnected to release the landing gear during recovery and not reconnected. Therefore, the hydraulic fluid level in the reservoir could not be determined prior to the accident, however, . once properly serviced with hydraulic fluid, the power pack functioned appropriately. It’s likely the power pack was not serviced to the proper level during the accident flight, which resulted in the failure of the landing gear to extend. During initial testing, the landing emergency release valve did not release hydraulic pressure when activated. Two bolts located on the valve bracket were missing lockwire. The bolts are supposed to be torqued and safety wired to prevent movement of the valve lever setting. The valve bracket and valve lever were at the extreme setting, which would produce minimal activation of the valve. The loose valve bracket bolts could affect the valve lever position by allowing the valve bracket to slide when actuating the valve. Once the valve bracket bolts were appropriately secured, the valve functioned properly with no anomalies noted. It’s most likely the valve bracket bolts were not installed properly with lockwire. Although the investigation identified other potential causes of the valve not functioning properly, including the rigging of the actuation cable to the landing emergency release valve and the valve possibly not being fully set to the closed position at an unknown time, the investigation was unable to determine the exact cause of the landing gear emergency release valve failure.
On February 28, 2020, about 1151 Pacific standard time, a Piper PA 46-350P airplane, N304LA, was substantially damaged when it was involved in an accident near San Jose, California. The flight instructor, private pilot, and two passengers were not injured. The flight was operated under the provisions of Title 14 Code of Federal Regulations Part 91, as a personal flight. According to the pilot receiving instruction, during the approach into San Martin Airport (E16), San Martin, California, the landing gear was unable to be extended and locked, despite several attempts. At that time, the flight instructor elected to divert to San Jose International Airport (SJC), San Jose California. En route to SJC, continued attempts to extend the landing gear were unsuccessful, and the flight instructor landed the airplane with the gear retracted. Postaccident examination of the airplane by a Federal Aviation Administration inspector, revealed substantial damage to the fuselage. Examination of the airplane’s landing gear system by a certified airframe and powerplant mechanic revealed that the hydraulic power pack used to operate the landing gear system had no fluid showing in the sight window for the reservoir level. The lack of hydraulic fluid was consistent with the hydraulic line being disconnected, to release the landing gear during recovery, and not reconnected. Therefore, the line was resecured, and the power pack was serviced with about a pint of appropriate hydraulic fluid. Afterwards, no leaks were noted in the system..Subsequently, the hydraulic pump circuit breaker was reset, and the landing gear was cycled from the retracted to the extended position with no anomalies noted. Landing gear extension was then attempted by using the emergency system. However, despite full movement of the emergency extension handle, the landing gear did not release. Additionally, during cycling of the landing gear, the power lead was disconnected in an attempt to reduce pressure at the emergency extension valve and make it operational. The reduced pressure in the system did not affect the emergency valve movement nor its nonoperational status. The hydraulic pack was drained and removed, in addition to the emergency extension valve and shipped to the manufacturer for further examination. Examination of the power pack revealed that the fluid level in the sight glass indicated no sign of fluid upon arrival. Further, the filler hole was found to be dry with no indication of fluid. The power pack had been updated per Piper SB964B, Hydraulic Power Pack Pressure Switch Replacement. The hydraulic power pack was initially bench tested in the “as received” condition with no visible fluid. The test system hoses, and pump were filled with an appropriate amount of hydraulic fluid, with the exception that no fluid was added to the power pack. Additionally, due to the lack of hydraulic fluid in the reservoir, the power pack was not cycled for more than 30 seconds to prevent overheating. Testing revealed that the pressure switches operated in accordance with specifications. Flow measured in gpm were measured at 300, 500, 800, 1100, and 1325 psi. The required minimum flow at 1325 psi is .46 gpm. However, a reading of .15 gpm was observed at 1325 psi. Next, the hydraulic pack was appropriately serviced with hydraulic fluid to the “full” level, as observed in the sight glass. The power pack was retested and met all requirements. The final flow at 1325 psi was .85 gpm which met the minimum flow of .46 gpm. Examination of the emergency release valve revealed that it was intact with all the required fittings in place. The valve was tested at low pressure and fluid flowed normally through the valve. The valve was then rotated to the CLOSED position to stop the flow, with no anomalies noted. The valve was now pressurized to 1600 psi and retained pressure with no leakage for the one-minute test requirement. However, when the valve was subsequently rotated to the OPEN position, the valve did not release the pressure as it should have Two bolts located on the valve bracket were missing lockwire. The bolts are supposed to be torqued and lockwired to prevent movement of the valve lever setting. The valve bracket and valve lever were at the extreme setting, which would produce minimal activation of the valve. The loose valve bracket bolts could affect the valve lever position by allowing the valve bracket to slide when actuating the valve. Additionally, the rigging of the actuation cable to the valve and the possibility that the valve was not fully set to the closed position were other potential causes of the valve not functioning properly. Before making any adjustment, it was observed that the two bolts were finger tight and that no measurable removal torque could be recorded. The valve bracket was then set with both bolts torqued to the proper specification. The valve was retested and in the OPEN position, the pressure was released. The valve functioned correctly with no anomalies noted. Further, it was not necessary to cut or loosen the valve bracket bolts when removing the valve from the aircraft.
The failure to properly service the hydraulic power pack prevented a normal landing gear extension. Contributing to the accident was the failure of the landing gear emergency release valve to function properly for reasons that could not be determined based on available information.
Source: NTSB Aviation Accident Database
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