Prop Strike, TBO, and What Makes an Engine Airworthy
During the annual inspection of a Cessna T210M, you learn the airplane suffered a propeller strike last month. The propeller was removed, overhauled by a propeller shop, and reinstalled. The engine is a Continental TSIO-520 showing 2,240 hours since major overhaul; the manufacturer's recommended time between overhaul is 1,700 hours. The engine maintenance manual contains a sudden-stoppage procedure requiring a crankshaft runout check, and crankshaft replacement if runout exceeds limits. That procedure appears in the maintenance manual but not in the Airworthiness Limitations section. There is no log entry documenting any inspection of the engine after the strike. The owner's position: 'TBO is only a recommendation under Part 91, and the prop is already fixed, so sign the annual.'
1. Standing alone, does 2,240 hours since overhaul make the engine unairworthy?
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No, not by itself. For a Part 91 operator, a recommended TBO in a manufacturer's maintenance manual is not a regulatory operating limit, and Section 43.16 makes mandatory only those inspections and maintenance tasks that appear in the Airworthiness Limitations section of the maintenance manual or instructions for continued airworthiness, or in FAA-approved alternative documents. Unless the ALS or an AD imposes a life limit on a specific part, exceeding a recommended TBO does not automatically ground the airplane.
But do not stop at 'legal.' Your job is to determine airworthiness, meaning the engine conforms to its type design and is in condition for safe operation. A high-time engine with normal oil consumption, good compression, clean screens, and stable parameters can be airworthy; one with a failing exhaust valve cannot. Document the basis for your finding, and mention in your remarks that the engine is past the recommended TBO so the owner's decision is informed.
2. Given the propeller strike, can you sign the annual as airworthy as the airplane sits?
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No. The TBO is a distraction; the sudden stoppage is the real issue. A propeller strike transmits loads through the flange into the crankshaft, and the manufacturer's instructions for continued airworthiness prescribe the investigation - typically a runout check and, if out of limits, crankshaft replacement. Section 43.13(a) directs you to the manufacturer's maintenance manual or instructions for continued airworthiness as the primary source of methods.
You have no evidence that the procedure was performed. You cannot determine that the engine conforms to its type design or is in condition for safe operation with a known, uninspected sudden stoppage in its recent history. Before you sign anything, check the engine ADs as well; several ADs impose their own sudden-stoppage or crankshaft requirements, and an AD would settle the argument outright.
Required action: perform the runout check per the manual. If within limits, record it under Section 43.9 with the readings. If out of limits, the engine comes off.
3. What documentation should exist before the airplane flies again, and what do you tell the owner about the propeller work?
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You want a chain that stands up to a later review: the propeller shop's work order or FAA Form 8130-3 or equivalent release documenting the overhaul and the blade and hub inspection; a Section 43.9 entry for the propeller removal and reinstallation with torque values and the dynamic balance or track check if performed; the engine sudden-stoppage inspection results with actual runout readings; the engine AD status statement; and your annual inspection entry, which may now carry the airworthy certification if everything checks out.
On the propeller: verify that the shop was appropriately rated for the work and that the propeller model and hub serial number match the aircraft's TCDS and the applicable propeller ADs. An overhaul tag is not proof of AD compliance; read it against the AD list.
And tell the owner plainly: the TBO argument was never the point. The airplane was unairworthy because a known sudden stoppage had not been investigated, not because the engine was over on hours.