FAA Aviation Mechanic Powerplant (AMP)PropellersMedium
A mechanic is installing a propeller hub onto the engine crankshaft flange. What method should be used when torquing the mounting bolts to ensure even seating and prevent hub distortion?
- ATorque only alternating bolts and leave the others finger-tight
- BFully torque one bolt at a time in a clockwise sequence around the hub
- CTighten all bolts by hand only, without using a torque wrench
- DTorque the bolts gradually in a crisscross (star) pattern up to the specified value
Show answer & explanationAnswer & explanation
Correct answer: D. Torque the bolts gradually in a crisscross (star) pattern up to the specified value
Propeller hub bolts, like other circular bolt patterns (e.g., cylinder heads, wheel lugs), must be torqued gradually and evenly using a crisscross (star) pattern in incremental steps to avoid distorting the hub and to ensure even clamping force. Fully torquing bolts sequentially or leaving bolts loose can warp the hub or cause uneven seating.
Why the other options are wrong
- A. All bolts must be torqued to specification, not left finger-tight.
- B. Sequential full torquing one bolt at a time can distort the hub.
- C. A calibrated torque wrench must always be used per the manufacturer's specified value.
Hub Bolt Torque Sequence
Propeller hub mounting bolts should be torqued gradually in incremental steps using a crisscross (star) pattern to ensure even seating and prevent hub distortion.
- Crisscross/star pattern used
- Torque applied gradually in increments
- Prevents hub warping/distortion
- Final torque per manufacturer specification
Memory trick: Star pattern, step by step — even pressure keeps the hub straight.