11.3 Powerplant, Propeller & Nondestructive Inspection Standards for the IA

11.3 Powerplant, Propeller & Nondestructive Inspection Standards for the IA

[!NOTE] The IA's powerplant role is jurisdictional first, technical second. Before evaluating a cylinder or a blade, establish who was permitted to perform the work and what data governed it. The most common enforcement finding in this area is not bad workmanship — it is work performed by someone without the privilege to perform it.

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Who May Do What to an Engine or Propeller

The Mechanic's Two Standing Limitations — 14 CFR 65.81(a)

A certificated mechanic may perform or supervise the maintenance, preventive maintenance, or alteration of an aircraft or appliance for which that person is rated — but excluding major repairs to, and major alterations of, propellers, and any repair to, or alteration of, instruments. Two consequences an IA applies constantly:

1. Propeller major repairs and major alterations are outside a mechanic's privileges entirely. They belong to an appropriately rated repair station or the manufacturer. An IA does not gain that privilege either — the IA's authority under 65.95(a)(1) is to inspect and approve for return to service, not to perform work the underlying certificate does not authorize.
2. Instruments may not be repaired or altered by a mechanic at all — not even minor repairs. Instrument work goes to a rated repair station or the manufacturer.

Section 65.81(a) also carries the "previously performed" rule: a mechanic may not supervise, or approve for return to service, work of a kind the mechanic has not satisfactorily performed at an earlier date, unless the ability is demonstrated to the Administrator or the work is done under the supervision of an experienced certificated mechanic or repairman.

Powerplant Major Repairs — Appendix A(b)(2)

The list is short and specific:

• (i) Separation or disassembly of a crankcase or crankshaft of a reciprocating engine equipped with an integral supercharger.
• (ii) Separation or disassembly of a crankcase or crankshaft of a reciprocating engine equipped with other than spur-type propeller reduction gearing.
• (iii) Special repairs to structural engine parts by welding, plating, metalizing, or other methods.

Note what is not on the list: splitting the case on an ordinary direct-drive, normally aspirated engine is not, by (b)(2)(i) or (ii), a major repair. The qualifiers — integral supercharger, non-spur reduction gearing — are the entire content of those two items, and an answer choice that omits them is wrong.

Propeller Major Repairs — Appendix A(b)(3)

Substantially longer, and worth reading as a list because propeller questions are drawn straight from it:

• (i) Any repairs to, or straightening of, steel blades
• (ii) Repairing or machining of steel hubs
• (iii) Shortening of blades
• (iv) Retipping of wood propellers
• (v) Replacement of outer laminations on fixed-pitch wood propellers
• (vi) Repairing elongated bolt holes in the hub of fixed-pitch wood propellers
• (vii) Inlay work on wood blades
• (viii) Repairs to composition blades
• (ix) Replacement of tip fabric
• (x) Replacement of plastic covering
• (xi) Repair of propeller governors
• (xii) Overhaul of controllable-pitch propellers
• (xiii) Repairs to deep dents, cuts, scars, and nicks, and straightening of aluminum blades

Contrast with refinishing wooden blades, which appears in the Appendix A(a)(3) propeller alteration discussion rather than as a major repair, and with routine dressing of minor nicks on aluminum blades within manufacturer limits, which is ordinary maintenance. The exam's favorite construction is to offer three propeller operations and ask which one is not major.

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Propeller Inspection Points for the IA

Under Part 43 Appendix D(h), the propeller group inspection covers the assembly for cracks, nicks, binds, and oil leakage; bolts for improper torquing and lack of safetying; anti-icing devices; and control mechanisms for improper operation, insecure mounting, and restricted travel.

Beyond the Appendix D minimum, an IA checks:

Blade diameter deserves emphasis. Every TCDS states a maximum and minimum propeller diameter. Dressing nicks removes material at the tip, and cumulative dressing over many years can carry a blade below the minimum. A propeller below the TCDS minimum diameter does not conform to type design, and there is no field repair that restores it.

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Engine Inspection Findings an IA Must Interpret

The compression test procedure and leak-path diagnosis are covered in Section 3.2. Beyond it:

• Metal on screens and in filters — Appendix D(d)(3) requires inspection for metal particles or foreign matter on screens and sump drain plugs. The character of the metal matters: fine grey paste is often normal wear, shiny flakes suggest bearing or gear distress, and steel slivers attracted to a magnet indicate a different source than non-magnetic aluminum or bronze.
• Exhaust system integrity — cracks in stacks and, critically, in a muffler shroud used as a cabin heat source, which is a carbon monoxide path into the cabin. This is a life-safety inspection item on every reciprocating single.
• Engine mounts — Appendix D(d)(4) requires inspection for cracks, looseness of mounting, and looseness of engine to mount. Welded mount repairs are major repairs (Section 9.3).
• Cylinder condition — beyond compression, borescope inspection for barrel scoring, valve face condition, and combustion deposits.
• Turbine oil systems — turbine engine lubrication systems are designed with an oil tank expansion space to accommodate foaming and thermal expansion. The required minimum expansion space is a design certification value from the engine airworthiness standards, not something a technician selects; the maintenance obligation is simply to service the tank to the manufacturer's specified level, which preserves that space. Overservicing a turbine oil tank defeats the expansion space and causes oil to be scavenged overboard.

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Nondestructive Inspection: Choosing a Method

AC 43.13-1B Chapter 5 covers nondestructive inspection (NDI). For the IAR test, the skill is matching method to defect and material:

Two selection rules answer most questions:

1. If the part is not ferromagnetic, magnetic particle is out. Aluminum, magnesium, austenitic stainless, and titanium require penetrant, eddy current, ultrasonic, or radiographic methods.
2. If the defect is not open to the surface, dye penetrant is out. Penetrant is a capillary-action method; it can only find what breaks the surface.

Where an AD or an ICA specifies a method and interval, that specification is mandatory (Chapter 7). An operator may not substitute a different NDI method for the one an AD requires without an approved AMOC (Section 4.1).

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High-Yield Exam Traps

• A mechanic may never perform a propeller major repair or major alteration, nor any instrument repair or alteration — § 65.81(a) removes both from the certificate.
• Appendix A(b)(2)(i) and (ii) are qualified: integral supercharger, or other than spur-type reduction gearing. Splitting an ordinary direct-drive case is not automatically a major repair under those items.
• Retipping wood propellers and straightening aluminum blades are major repairs under Appendix A(b)(3).
• A propeller below TCDS minimum diameter is unairworthy and cannot be repaired back into limits.
• Dye penetrant finds only surface-breaking defects; magnetic particle works only on ferromagnetic material.