Flight Control Systems — Page 169, Lesson 217

Right, let's get into the Flight Control Systems chapter. We're starting with an official Civil Aviation Authority leaflet on control systems, and I want to walk you through it carefully because it sets the professional standard for how we inspect and certify these systems. First, the introduction. This leaflet provides general guidance and advice on inspection procedures for control systems. And note the three categories it covers: manually operated, power assisted, or power operated. So a control system can be purely mechanical, or it can have hydraulic or electrical assistance, or it can be fully powered. And crucially, this leaflet is meant to be read in conjunction with the relevant approved drawings and manuals for the specific aircraft. In other words, this is the general framework, but the aircraft's own documentation is always the authority. Now, the formal definition. A control system is defined as a system by which the flight attitude or the propulsive force of an aircraft is changed. Let me unpack that. Flight attitude means the orientation of the aircraft in space — pitch, roll, yaw. Propulsive force means thrust. So a control system is anything that changes how the aircraft is oriented or how much thrust it produces. Then we get into what's included in the flight control system for the purpose of duplicate inspection. This is important. The flight control system includes the main control surfaces — that's your ailerons, elevators, rudder. It includes lift and drag devices — so flaps, slats, spoilers, speed brakes. It includes trim and feel systems — trim tabs and the artificial feel units that give the pilot control forces. It includes any flight control lock systems — the devices that lock the controls when the aircraft is parked. And it includes the associated operating mechanisms and controls — all the linkages, cables, and levers that connect the pilot to those surfaces. For rotorcraft, the definition is specific. The flight control system includes the mechanisms used by the pilot to control collective pitch, cyclic pitch, and yaw. Collective pitch changes the pitch of all rotor blades simultaneously to control vertical movement. Cyclic pitch changes blade pitch cyclically to control the tilt of the rotor disc for directional movement. And yaw is controlled by the tail rotor or other anti-torque system. Now, the engine control system. This includes the primary engine controls and related control systems — for example, throttle controls, fuel cock controls, and oil-cooler controls — plus the mechanisms the crew uses to operate them. So it's not just the throttle lever in the cockpit; it's the entire linkage from that lever back to the engine. Now we come to the heart of this leaflet: duplicate inspection. This is a critical concept. A duplicate inspection of a vital point or control system is defined as an inspection which is first made and certified by one qualified person, and subsequently made and certified by a second qualified person. So two separate qualified individuals each perform the inspection independently, and each certifies it. This is a double-check system to catch errors. And here's the note on vital point. A vital point is any point on an aircraft at which single incorrect assembly could lead to catastrophe — that is, result in loss of aircraft and/or fatalities. This is referenced to BCAR Section A, Chapter A5-3, which is the British Civil Airworthiness Requirements. So a vital point is a single point of failure where one mistake in assembly could kill people. And then the final line of this excerpt is a critical operational rule. Components, systems, or vital points subject to duplicate inspection must not be disturbed or re-adjusted between the first and second part of the inspection. Let me emphasize that. Once the first inspector has certified their inspection, nothing can be touched. No adjustment, no disturbance. The second inspector must find the system exactly as the first inspector left it. Otherwise, the duplicate inspection is invalid because the second inspection wouldn't be checking the same configuration. So to summarize what we've covered: the definition of a control system, what's included in the flight control system and engine control system, the definition of duplicate inspection, the definition of a vital point, and the rule that nothing may be disturbed between the two inspections. That's the foundation for everything else in this chapter.