Loss of engine coolant caused the crash of an MQ-1B Predator Jan. 30, 2012, in Afghanistan, according to an Air Combat Command Abbreviated Accident Investigation Board report released May 29, 2012.
According to the report, the coolant pump supply line failed, releasing the engine’s coolant. As the coolant supply decreased, the cylinder head temperature increased excessively. Heat expansion of the cylinder walls prevented a proper seal, reducing power output and preventing sustained flight. The abnormal temperature indications worsened, and the aircraft experienced a significant loss of thrust and fell into an uncontrolled descent. The crew regained control long enough to guide it to a forced landing.
During the investigation, the board president also found two contributing factors. First, the mishap maintainer failed to detect damage on the coolant supply line and the oil cooler-to-pump line during a 60-hour engine inspection Jan. 26, 2012.
Post-mishap analysis found evidence that the oil and coolant lines were chafing against each other, which ultimately led to the coolant line failure. Additionally, the second mishap pilot failed to ensure the line-of-sight control link transmitter was powered off as he turned the ground antenna toward the aircraft. The 1,200 feet of altitude lost in the ensuing unintentional spiral prevented a safe recovery.
The aircraft and one air-to-ground Hellfire missile were destroyed on impact. The damage was assessed at approximately $4.5 million. There were no injuries, or damage to government or private property.