Pumped

This aircraft was equipped with a turbonormalizing system, which requires a fuel pump with an aneroid compensator to regulate the mixture replaces the original pump. On this installation, the fuel mixture cam profile was erroneous. Fuel flow rate increased normally from idle cutoff to approx 80 percent of mixture-lever range of motion where fuel flow is at maximum. Then the fuel ratio decreases as lever continues toward maximum position: 80 percent mixture provides 37.5 gph; 100 percent provides 35.5 gph.

Key Takeaways:

• Multiple aircraft experienced fuel system malfunctions, including an erroneous fuel mixture cam profile, fuel contamination from a leaking boost pump, and abnormally high fuel pressure from an electric pump.
• Engine-driven fuel pumps were also a source of issues, with reports of leaks from relief valve gaskets and fuel in pressure lines.
• One incident involved a landing gear hydraulic pump failure, resulting in partial gear retraction and compromised directional control and braking capability.

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