Which statement best describes when the ECS knob should be set to HEAT EXCHANGE ONLY?

Which statement best describes when the ECS knob should be set to HEAT EXCHANGE ONLY?

• A. As directed by Checklist/AFM
• B. During takeoff
• C. During landing
• D. When icing is present

Answer: (A)

The setting of HEAT EXCHANGE ONLY is a controlled operating mode that must be commanded exactly as the flight manual or checklist directs. It isn’t a routine switch you flip for a generic phase of flight or for icing in general; it’s a special mode used only when the procedures prescribe it. Because the maneuver is defined by the approved checklist/AFM, following those exact instructions ensures the Environmental Control System functions safely and within its design limits. In practice, you wouldn’t rely on a generic rule like “use this during takeoff or landing” or “use when icing is present.” Those conditions may be covered by other procedures or system settings in the AFM, but the decision to set HEAT EXCHANGE ONLY should come from the checklist guidance.

The setting of HEAT EXCHANGE ONLY is a controlled operating mode that must be commanded exactly as the flight manual or checklist directs. It isn’t a routine switch you flip for a generic phase of flight or for icing in general; it’s a special mode used only when the procedures prescribe it. Because the maneuver is defined by the approved checklist/AFM, following those exact instructions ensures the Environmental Control System functions safely and within its design limits.

In practice, you wouldn’t rely on a generic rule like “use this during takeoff or landing” or “use when icing is present.” Those conditions may be covered by other procedures or system settings in the AFM, but the decision to set HEAT EXCHANGE ONLY should come from the checklist guidance.