In which circumstance must the direction of turns be included in a holding clearance?

Including the direction of turns in a holding clearance is essential for clear communication and safety in situations where the standard assumptions do not apply. When left turns are to be made, this must be explicitly stated in the clearance to avoid confusion, especially since right turns are typically the default unless specified otherwise.

In the context of holding patterns, if the clearance indicates left turns, it ensures that the pilot understands precisely how to operate within the holding pattern. This reduces the risk of misunderstandings that could lead to dangerous situations or conflicts with other aircraft.

Other circumstances may not require the same level of specificity — for example, non-charted holding patterns may be described through other means, and pilots may have their preferences for turns, but left turn specifications are a clear directive that must be communicated effectively.