What is the required cooling off time after 60 seconds of engine on-time during a ground start?

The required cooling off time after 60 seconds of engine on-time during a ground start is indeed 5 minutes. This limitation is critical to ensure that the engine components, particularly the turbine and other high-temperature parts, do not overheat and suffer potential damage. Engine operating limits are established to maintain the integrity and safety of the engine during start-up procedures, especially in ground operations where the engines may not receive the same level of cooling airflow as they would in flight.

While shorter cooling periods might seem sufficient, they do not provide adequate time for the engine to cool down properly, leading to potential overheating and increased wear. The 5-minute cooling period is designed to mitigate these risks effectively, ensuring that the engine can be started again safely without compromising performance or safety. In this context, understanding the importance of adhering to these limits is crucial for safe aircraft operation and maintenance protocols.