When does the life limit cycle for an aircraft engine begin?

The life limit cycle for an aircraft engine begins upon installation on the wing and completion of ground tests because this marks the point at which the engine starts being utilized in its intended operational environment. At this stage, the engine undergoes various stressors and operational conditions that contribute to its wear and tear. This is critical for maintenance planning, tracking life limits, and ensuring the safety and reliability of the engine.

Prior to installation, while the engine may have been manufactured and tested in a controlled environment, it has not yet been subject to the operational factors that define its life cycle. The first flight is also significant, but it is post-installation and ground tests that officially initiate the counting of life limits. Refurbishment resets certain components, but does not commence a new life cycle unless it involves significant overhauls that might warrant a new life tracking.