How long should the dry motor cycle be repeated after five sequential motorings?

The correct answer is based on the recommended procedures for dry motoring in the ERJ 170/175 operational limits. After conducting five sequential motorings, it is necessary to allow the aircraft’s systems to cool down properly. The guideline dictates a cooldown period of 15 minutes before performing another cycle. This cooldown is essential to prevent overheating of the engine components and to ensure safe operational limits are maintained.

This practice acknowledges the thermal stress imparted by continuous motoring operations, highlighting the importance of adhering to the specified cooldown intervals to maintain engine integrity and reliability. A shorter cooldown period, as suggested in other options, would not provide sufficient time for the components to recover from the heat generated during operation, potentially leading to damage or inadequate performance in subsequent motorings.