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During which phases of flight is the IAS hold mode allowed to be engaged and maintained?
  • A
    Exclusively during climbs and descents.
  • B
    Solely during turns.
  • C
    Limited to climbs, descents, and power changes.
  • D
    Permissible during climbs, descents, turns, and power changes.

Refer to figures.
The basic function of an Automatic Flight Control System (AFCS) is to provide long-term stability for "hands off" flight of the helicopter. This is achieved using a basic inner loop control system with reference to attitude information to control the aircraft around its Center of Gravity and hold the altitude and heading (pitch and roll control). This would be a 2-axis autopilot. However, large commercial helicopters use a 4-axis system incorporating collective and yaw control.

The Automatic Flight Control System (AFCS), except for the basic function, can also control airspeed, climb and descent, navigation commands, engine power, and hover. These are termed flight path modes, and the control system is modified by adding an outer loop control.

The outer loop system drives parallel actuators to operate the flight control systems. The outer loop modes are selected via several labeled buttons on an AFCS control panel.

Specifically, IAS is the Indicated Airspeed hold mode. Pushing the IAS button commands the AFCS to maintain the IAS during selection by generation of pitch commands. The IAS mode can be engaged and held during climbs, descents, turns, and power changes.

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