What is the ON/OFF pattern for the first engine motoring attempt on the ground?

What is the ON/OFF pattern for the first engine motoring attempt on the ground?

• A. 90 Seconds ON, 5 Minutes OFF
• B. 60 Seconds ON, 5 Minutes OFF
• C. 120 Seconds ON, 10 Seconds OFF
• D. 30 Seconds ON, 5 Minutes OFF

Answer: (A)

Motoring the engine on the ground is a careful check to ensure the engine can rotate freely and that the lubrication and starting systems are working before a normal start. For the first motoring attempt, you spin the engine with the starter for a defined period without fuel flow, then give it a substantial off interval to cool and allow oil pressure and temperatures to normalize before trying again. Why 90 seconds on is used: that duration is long enough to bring the engine up to a low, controlled speed and reveal any binding, roughness, or abnormal noises. If the engine struggles or makes unusual sounds, you stop the test and investigate. Why 5 minutes off is used: this cooldown period protects the starter and accessories from overheating and gives the oil system time to stabilize again. It also provides a safe window before the next motoring cycle or a subsequent start, reducing stress on the engine and its components. Other patterns either would not provide enough running time to verify operability or would not give sufficient cooling, increasing the risk of damage. That balance is why the 90 seconds on, 5 minutes off sequence is used for the first engine motoring attempt.

Motoring the engine on the ground is a careful check to ensure the engine can rotate freely and that the lubrication and starting systems are working before a normal start. For the first motoring attempt, you spin the engine with the starter for a defined period without fuel flow, then give it a substantial off interval to cool and allow oil pressure and temperatures to normalize before trying again.

Why 90 seconds on is used: that duration is long enough to bring the engine up to a low, controlled speed and reveal any binding, roughness, or abnormal noises. If the engine struggles or makes unusual sounds, you stop the test and investigate.

Why 5 minutes off is used: this cooldown period protects the starter and accessories from overheating and gives the oil system time to stabilize again. It also provides a safe window before the next motoring cycle or a subsequent start, reducing stress on the engine and its components.

Other patterns either would not provide enough running time to verify operability or would not give sufficient cooling, increasing the risk of damage. That balance is why the 90 seconds on, 5 minutes off sequence is used for the first engine motoring attempt.