What must occur before repeating the dry motoring sequence after five attempts?

The requirement of a 15-minute cool-down period after five attempts of the dry motoring sequence is crucial for the engine's health and safety. This cooling period allows time for the engine components to dissipate heat generated during the motoring attempts, preventing potential damage from overheating. By ensuring that the engine has adequate time to cool, it helps to maintain the integrity of parts such as the cylinder walls and pistons, which may otherwise be subjected to excessive thermal stress. This procedure is part of standard operating protocols to enhance reliability and prevent mechanical failures in the aircraft engine during ground operations.