F/A-18A/B/C/D Main Landing Gear Control Unit Hydraulic 2A Supply Line Pressure Spikes and Emergency Port Restrictor Ground and Flight Tests Evaluation

摘要

The F/A-18A-D fleet has been experiencing cracked brackets on the right main landing gear (MLG) wheel well hydraulic 2A (HYD 2A) pressure supply line. Investigations revealed that hydraulic pressure spikes in the HYD 2A supply line may be a contributing factor to the bracket failure. Some bracket failures have led to HYD 2A supply line failures. F/A-i 8E/F testing determined that landing gear circuit breaker resets and improper gear retractions following an emergency gear extension caused pressure spikes. A suspected but unproven cause of pressure spikes is the first engine start of the day. For this test, a production F/A-18A-D landing gear control unit (LGCU) was modified at NADEP north Island to accept a restrictor within the emergency port of the valve. The Boeing and Northrop Grumman developed restrictors were designed to control emergency spool movement and eliminate pressure spikes in the HYD 2A supply line. Three restrictors were designed with increasing levels of restriction (2000, 5500, and 9000 lohm). The elimination of pressure spikes is expected to reduce or eliminate the hydraulic line bracket failures that have been occurring in the USN/USMC fleet and FMS aircraft.