What is the primary hazard when performing a compression check with the cylinder under test?

• A. Propeller could rotate and strike.
• B. Fire hazard.
• C. Electrical shock.
• D. Oil leaks.

Answer: (A)

Rotating the propeller during a compression check is the primary hazard. Cranking the engine to measure cylinder pressure turns the crankshaft, and the prop can begin to move. If the prop isn’t secured, it can strike a person or cause injury or damage. To prevent this, ground or disable the ignition and secure the propeller blade(s) with a strap or have someone hold them, and stay clear of the blade arc. The other listed hazards aren’t the main concern for this procedure because ignition is disabled and there’s no fuel or active electrical source driving the test.