Propeller vibration and incomplete hub records at release
A turbocharged piston single has a three-blade constant-speed propeller. After blade dressing and a dynamic balance, the pilot reports 0.8 IPS vibration at 2 300 rpm; the previous reading was 0.15 IPS. Track is 4 mm against a 6 mm limit, blade angles are within 0.2 degrees, and spinner runout is 0.6 mm. The propeller hub has a calendar overhaul limit of 10 years. The logbook shows overhaul 12 years ago, but the owner has an invoice for a hub overhaul 3 years ago that was never entered. An airworthiness directive against the hub serial number is not recorded, and the owner cannot confirm compliance. The engine mounts are 8 years old, and the engine has 40 h since top overhaul. The aircraft is presented for a maintenance release. The AME must decide whether to release the aircraft and how to handle the records and vibration.
1. Assess the vibration. What are the likely causes and what tests would you do?
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A rise from 0.15 IPS to 0.8 IPS is significant, even though track, blade angles and spinner runout are within limits. Those checks reduce the likelihood of a gross blade or spinner problem, but they do not prove the propeller is serviceable. I would suspect dynamic balance, a blade repair that changed mass distribution, a loose or deteriorated engine mount, a propeller governor or crankshaft vibration issue, or an ignition or exhaust fault that appears at 2 300 rpm. I would repeat the balance check, inspect the blades for damage and repair records, check mount condition and torque, and run the engine through the rpm range while monitoring vibration. I would not release the aircraft at 0.8 IPS until the source is found and corrected.
2. How do you resolve the propeller overhaul and AD records?
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The invoice is not an airworthiness record by itself. I would verify the hub serial number, the overhaul date and the approved shop from the invoice and, if necessary, obtain a duplicate overhaul certificate. I would then enter the overhaul in the logbook with the correct date and reference. For the AD, I would check the hub serial number against the AD applicability and obtain a compliance record from the overhaul shop or a previous maintainer. If compliance cannot be established, the aircraft cannot be released on the assumption that the AD was done. The calendar overhaul history matters because the logbook alone shows 12 years, which would exceed the 10-year limit. The physical records and the data plate must agree before any release decision.
3. What documentation and release decision are appropriate?
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I would not issue a maintenance release until the vibration is corrected and the propeller overhaul and AD status are documented. The release record should identify the propeller serial number, the overhaul date and shop, the AD compliance reference, the balance and track results, and the corrective action for the vibration. If the overhaul cannot be verified, the propeller should be treated as overdue and removed from service until the records are resolved. If the AD cannot be confirmed, the aircraft is not airworthy for release. A special flight permit might be considered only for a ferry to a repair facility, with CAA approval and appropriate restrictions, not for normal service. The AME should also record the engine mount inspection and the post-balance vibration reading.