What happened
On May 10, 2019, a Learjet 60, registration LV-GCK, operating as a non-scheduled commercial flight, experienced a dual hydraulic system failure during a flight from Rosario to Santiago. While en route, the crew noticed low pressure in the right hydraulic system, followed five minutes later by low pressure in the left system. The crew diverted to El Plumerillo International Airport in Mendoza.
During the approach to runway 36, the aircraft's configuration was compromised; while the landing gear deployed normally, the flaps only extended to 8 degrees due to the lack of hydraulic pressure. The aircraft touched down between the threshold and the touchdown zone. Despite the use of the emergency braking system by the captain, the aircraft failed to stop within the paved surface, overshooting the runway and coming to rest on a dirt surface approximately 2/20 meters beyond the end of runway 18.
The investigation
The investigation focused on the mechanical failure and the landing performance. Inspectors found that the hydraulic reservoir was empty. The leak originated from a check valve on the pressure line from the right engine, where the connection lacked sufficient torque to maintain a seal. This loosened over time due to operational pressure cycles. Additionally, metallic particles were found in the hydraulic system filters.
Regarding the landing, investigators determined that the available landing distance (LDA) was reduced to 2,790 meters due to a permanent runway threshold displacement caused by an adjacent obstacle. While the aircraft traveled approximately 2,820 meters, the theoretical distance required for the specific aircraft configuration and weather conditions was calculated at 3,252.5 meters.
Findings
- The primary cause of the hydraulic fluid loss was a leaking check valve connection that had not been properly torqued.
- The crew did not declare an emergency to Air Traffic Control, which increased their workload and prevented them from utilizing priority assistance and ground service alerts.
- The aircraft's landing configuration (8-degree flaps) and the reduced available runway distance contributed to the inability to stop on the pavement.
- The maintenance program did not require torque inspections of these specific hydraulic connections, meaning the loose fitting went undetected during the previous inspection.