What action should the PF refrain from doing before confirming with the other crewmember?

The most appropriate action for the PF (Pilot Flying) to refrain from is executing reversible actions before confirming with the other crewmember. This is due to the critical nature of ensuring that any decisions made, particularly those that involve changes to the aircraft's configuration or state, are mutually agreed upon by both pilots.

Executing reversible actions, such as adjustments to the flight controls or systems settings, can have immediate effects on the aircraft's operation. If one pilot proceeds without confirmation from the other, it might lead to unintended consequences, especially if there is any ambiguity or misunderstanding about the current situation or the actions being taken.

In contrast, flying the aircraft, consulting the checklist, and communicating via radio are essential responsibilities that typically require coordination and collaboration, but these actions often can be performed in tandem with the confirmation process. Therefore, it is crucial for the PF to prioritize clear communication and confirmation before making reversible changes that might impact flight safety.