What describes hydraulic lock in an aircraft engine?

• A. Oil drained past piston rings and filled the combustion chamber, causing a lock when the crank is turned.
• B. Air within a cylinder causing temporary misfire.
• C. A spark plug fouling due to oil contamination.
• D. Overheating due to detonation.

Answer: (A)

Hydraulic lock occurs when an incompressible liquid fills a cylinder, so the piston cannot be moved by the crank. In aircraft engines, oil can leak past piston rings and fill the combustion chamber. When you attempt to turn the crank, the liquid resists compression instead of air, effectively locking the motion and potentially causing damage if forced. The description of oil leaking past rings into the combustion chamber and creating a lock when the crank is turned matches this phenomenon in full.