What happened
During a return flight to the departure airport following a routine aerial drop, the flight crew identified a total loss of hydraulic pressure. The captain observed the pressure gauge at zero, and the first officer confirmed that the main hydraulic fluid reservoir was empty. In response to the emergency, the crew initiated the emergency gear extension procedures. During this process, the crew diverted to a nearby airport with a longer runway and more extensive emergency services, preparing for a no-flap landing.
As part of the emergency checklist, the first officer attempted to install a pin in the nosewheel landing gear. The main landing gear was successfully extended using the emergency release, providing three down-and-locked indications. While the aircraft landed without incident, the nosewheel landing gear collapsed during the landing roll, leaving the aircraft in a nose-low position.
Findings
Post-accident investigations revealed that the nosewheel landing gear pin had become disengaged from the nosewheel jury strut, and the pin was missing from the scene. The disengagement of this pin was the primary reason for the gear collapse. It was noted that the first officer had to perform the pin installation in a confined area while the nose gear door was open and the gear was extended. Because the pin featured a red flag, the high-velocity airflow during flight may have caused the flag to vibrate, potentially dislodging the pin after its installation.
Additionally, investigators found evidence of a hydraulic fluid leak near the right engine cowling drain. The investigation identified a crack in the right engine hydraulic pump case and a partially extruded backup ring, which suggested the hydraulic system had experienced overpressurization. The specific cause of the overpressurization remained undetermined.