This SAE Aerospace Recommended Practice (ARP) provides guidance in the design, development, qualification test, process control and production acceptance test for flight critical control valve (FCCV) design used in military flight control servoactuators where loss of single valve control could cause a catastrophic failure resulting in death, permanent total disability, and/or financial loss exceeding a defined contractual limit. The FCCV, which is one element of a flight control actuator servo control loop, is a variable position control valve which modulates fluid into and out of the servoactuator power stage cylinders. The FCCV may be mechanically driven by either a mechanical flight control system as shown in FIGURE 1 or hydraulically driven from electro-hydraulic servo valve (EHSV) modulation control flow as shown in FIGURE 2. This type of control valve is not an EHSV or a direct drive valve (DDV).