What happened
On 27 January 2015, a Convair CV-580, registration N151FL, was performing a commercial cargo flight approaching Owen Roberts International Airport in the Cayman Islands. During the approach, the crew identified that the hydraulic system fluid levels were abnormally low. Following established procedures, the crew notified Air Traffic Control of a delay to the landing to perform necessary checklists regarding the fluid loss.
Due to the low fluid levels, the landing gear had to be deployed via free-fall, and the flaps could only be partially extended. After completing the required checklists and confirming the gear was down and locked, the aircraft landed on Runway 26. During the final stages of the landing roll, the crew experienced a total loss of nosewheel steering and a lack of braking effectiveness. Consequently, the aircraft drifted off the right side of the runway and came to a stop on the grass, approximately 150 ft from the runway centerline. There were no injuries to the crew and no damage to the aircraft.
The investigation
The investigation focused on the cause of the hydraulic fluid depletion and the subsequent failure of the braking system. Investigators identified a leak in the right main landing gear actuator as the source of the fluid loss.
To manage the leak, the crew had operated the Bypass selector as per the company checklist. This action isolated most components to preserve remaining fluid for essential services, but it also removed the availability of nosewheel steering. It was determined that the remaining hydraulic fluid was likely exhausted during the attempt to extend the flaps. This left the aircraft relying solely on the hydraulic accumulator and the emergency pneumatic pressure bottle for braking.
Findings
- The hydraulic fluid depletion was caused by a leak in the right main landing gear actuator.
- The use of the Bypass selector, while necessary to preserve fluid, resulted in the loss of nosewheel steering.
- The remaining hydraulic fluid was likely depleted by the partial extension of the flaps.
- A defective valve within the anti-skid control box prevented the brakes from functioning when using the hydraulic accumulator or the emergency pneumatic pressure system.