FAA Aviation Mechanic Powerplant (AMP)Engine InspectionHard
A mechanic measures crankshaft flange runout using a dial indicator while slowly rotating the crankshaft, obtaining a total indicator reading (TIR) of 0.006 inch. The manufacturer's overhaul manual specifies a maximum allowable flange runout of 0.005 inch TIR. What action should the mechanic take?
- AAverage the reading over multiple rotations to bring it within limits
- BIncrease the propeller flange bolt torque to compensate for the runout
- CAccept the crankshaft since 0.006 inch is close enough to the limit
- DReject the crankshaft flange because the runout exceeds the 0.005 inch limit
Show answer & explanationAnswer & explanation
Correct answer: D. Reject the crankshaft flange because the runout exceeds the 0.005 inch limit
A TIR of 0.006 inch exceeds the manufacturer's maximum allowable runout of 0.005 inch, so the crankshaft flange does not meet specification and must be rejected; excessive flange runout can cause propeller vibration and eventual crankshaft fatigue failure.
Why the other options are wrong
- A. Averaging readings does not change the actual measured runout condition.
- B. Bolt torque has no effect on correcting an out-of-round or bent flange.
- C. Runout limits are hard tolerances; being close does not make it acceptable.
Crankshaft Flange Runout Check
Flange runout is measured with a dial indicator while rotating the crankshaft to ensure the propeller mounting surface is true; exceeding the manufacturer's TIR limit requires rejection of the crankshaft.
- Measured using a dial indicator and total indicator reading (TIR)
- Excessive runout causes propeller vibration and crankshaft fatigue
- Limits are specified in the manufacturer's overhaul/service manual
- Runout cannot be corrected by torque adjustment; crankshaft must be repaired/replaced
Memory trick: 'Over the Limit, Out It Goes' — exceeding TIR means the crankshaft is rejected.