What is the waiting period after shutdown before checking the APU oil level?

The correct answer regarding the waiting period after shutting down the Auxiliary Power Unit (APU) before checking the oil level is one hour. This waiting period is crucial for allowing the engine oil to settle within the APU, which provides an accurate oil level reading.

When the APU operates, its oil is circulated and may not reflect the true level when the engine is running due to agitation and movement. By waiting for one hour after shutdown, it ensures that any oil that may have been splashed around during operation has settled back into the oil reservoir, allowing for a proper assessment of the oil level. This practice helps prevent misreading the oil level, which could lead to operational issues if the level is inaccurately assessed. The other suggested durations, while they may seem reasonable, do not align with the manufacturer’s specifications or standard maintenance practices for accurate assessments in aircraft maintenance.