How long should you wait after engine shutdown before checking MBG oil level?

After an engine shutdown, it's important to wait before checking the Main Gearbox (MBG) oil level to ensure an accurate reading. Waiting 30 minutes to 2 hours is ideal because it allows the oil that may be dispersed throughout the system to return to the sump where it can provide a truthful measure of the oil level.

During operation, engine components heat up, and oil can be agitated and foamed due to movement and circulation. Immediately checking the oil level after shutdown can result in an inaccurate reading, as the oil may still be in suspension or not fully settled. Thus, allowing adequate time for the oil to settle ensures that the measurement reflects the true oil level in the gearbox, which is crucial for proper operation and maintenance of the aircraft.

This time frame balances the need for a sufficient period for the oil to calm down while not delaying maintenance checks excessively. Other durations, such as only 10-15 minutes, are insufficient for the oil to return fully, while waiting for over 2 hours may unnecessarily postpone necessary checks.