FAA Aviation Mechanic Powerplant (AMP)Engine InspectionMedium
During a propeller inspection, a mechanic rotates a two-blade fixed-pitch aluminum propeller and marks the position of each blade tip against a fixed reference point to check tracking. If the manufacturer publishes no specific tolerance, what is the generally accepted maximum allowable difference between blade tip tracks?
- A1/16 inch
- B1 inch
- C1/4 inch
- D1/2 inch
Show answer & explanationAnswer & explanation
Correct answer: A. 1/16 inch
Per general industry and AC 43.13-1B guidance, propeller blade tips should track within 1/16 inch of one another unless the manufacturer specifies a different tolerance; excessive out-of-track condition causes vibration and imbalance.
Why the other options are wrong
- B. 1 inch is an extreme value never accepted for tracking tolerance.
- C. 1/4 inch is far too loose and would produce noticeable vibration.
- D. 1/2 inch would be grossly out of tolerance for propeller tracking.
Propeller Blade Tracking
Tracking checks that all propeller blade tips travel in the same rotational plane; excessive out-of-track causes vibration.
- Default tolerance is 1/16 inch unless manufacturer states otherwise
- Measured by rotating prop against a fixed pointer
- Out-of-track can result from bent blades or hub wear
- Tracking differs from static/dynamic balance
Memory trick: 'Sixteenth or Shake' — more than 1/16 inch off and the airplane shakes.