What happened
While operating in the cruise phase of flight, the flight crew observed that the number 1 hydraulic utility fluid quantity had dropped below the low red mark on the system gauge. In response to the loss of pressure, the crew transitioned operations to the secondary hydraulic system and initiated a diversion to a nearby airport.
The aircraft landed at the diversion airport without incident, with no injuries reported. The flight crew noted that this event marked the second time during that day that the number 1 hydraulic system fluid level had decreased. Prior to the most recent departure, maintenance personnel had replenished the hydraulic fluid in the system. During that previous servicing, the crew ran the engines and cycled the flight controls while maintenance staff performed a leak inspection; however, no leaks were identified at that time, and the aircraft proceeded on its scheduled flight leg.
The investigation
Following the diversion, maintenance personnel conducted an inspection of the aircraft's hydraulic systems. The investigation revealed that a hydraulic line leading to the flap drive motor had been chafed through, resulting in the fluid leak.