When should engine anti-ice be activated?

Activating engine anti-ice is crucial for preventing ice accumulation on engine components, which could jeopardize the aircraft's performance and safety. The correct situation to activate this system is when the temperature is below 5 degrees Celsius and icing conditions are present. This temperature threshold is significant because it indicates a higher likelihood of ice formation, particularly in moist air, which can create dangerous in-flight situations.

In other conditions such as flying over a frozen lake, while the temperature might be low, it does not necessarily mean that icing conditions are present, making a general activation of anti-ice unnecessary. Similarly, heavy rain conditions may not directly correlate with ice formation unless temperatures are also conducive to icing. Thus, the specific criteria of temperature and associated icing conditions are essential for determining when to activate the engine anti-ice system properly.