When should the ECS knob be set to HEAT EXCHANGE ONLY?

When should the ECS knob be set to HEAT EXCHANGE ONLY?

• A. When directed by Checklist/AFM
• B. On takeoff
• C. During engine start
• D. During landing

Answer: (A)

Heat exchange only is a special way the environmental control system can operate, using the heat exchanger to warm cabin air without engaging the normal conditioning packs. This mode is not part of normal operation and can change how temperature and airflow are managed, so it must be used only when the flight manual or checklist specifically directs it. That’s why the correct approach is to set it to heat exchange only only when instructed. It isn’t intended for routine phases like takeoff, engine start, or landing unless the procedure calls for it.

Heat exchange only is a special way the environmental control system can operate, using the heat exchanger to warm cabin air without engaging the normal conditioning packs. This mode is not part of normal operation and can change how temperature and airflow are managed, so it must be used only when the flight manual or checklist specifically directs it. That’s why the correct approach is to set it to heat exchange only only when instructed. It isn’t intended for routine phases like takeoff, engine start, or landing unless the procedure calls for it.