14.5 Special Inspections & Life-Limited Parts

14.5 Special Inspections & Life-Limited Parts

Quick Answer: A special inspection is triggered by an event, not by an interval. FAA-H-8083-32B separates two of them precisely: sudden stoppage is a "very rapid and complete engine stoppage" in which rpm goes to zero in less than one complete revolution of the propeller, and it "usually requires replacement or disassembly and inspection as per manufacturer's instructions." Sudden reduction in speed occurs when a blade strikes an object at low rpm, "the foreign object is cleared and the engine recovers rpm and continues to run," and it triggers a defined inspection sequence: external inspection, oil screens and drained oil checked for metal, a crankshaft or propeller-shaft runout check with a dial indicator that has 1/1,000-inch graduations, a blade track check, and a ground run followed by a re-check for metal. Separately, 14 CFR § 43.10 defines a life-limited part as "any part for which a mandatory replacement limit is specified in the type design, the Instructions for Continued Airworthiness, or the maintenance manual," and requires that a part removed from a type-certificated product be controlled by a method that deters installation after it has reached its life limit.

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Special Inspections Are Conditional, Not Scheduled

Section 14.1 covered the 100-hour, annual, and progressive inspections, which run on time in service or calendar months. A special inspection runs on something that happened. The list of triggers is engine-specific and lives in the manufacturer's data, but the recurring ones are:

The governing regulation is the same in every case. 14 CFR § 43.13(a) requires the person performing maintenance to use the methods, techniques, and practices prescribed in the current manufacturer's maintenance manual or Instructions for Continued Airworthiness, or other methods acceptable to the Administrator. A special inspection improvised from general practice is not a special inspection.

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Sudden Stoppage Versus Sudden Reduction in Speed

This pairing is the most heavily tested item in the whole topic, because the two events look similar to a witness and are treated completely differently by the manufacturer.

Sudden Stoppage

"Engine sudden stoppage causes a very rapid and complete engine stoppage... Either can be caused by engine seizure or by one or more of the propeller blades striking an object in such a way that revolutions per minute (rpm) goes to zero in less than one complete revolution of the propeller. Sudden stoppage may occur under such conditions as complete and rapid collapse of the landing gear, nosing over of the aircraft, or crash landing."

The internal damage list the handbook names is specific: "cracked propeller gear teeth, gear train damage, crankshaft flyweights becoming detuned or misalignment, or damaged propeller bearings." The phrase flyweights becoming detuned connects directly to Section 2.2 — a pendulum damper that has been shock-loaded no longer absorbs the harmonic order it was tuned for, and the crankshaft is then exposed to torsional fatigue that no external inspection will reveal.

"When sudden stoppage occurs, the engine usually requires replacement or disassembly and inspection as per manufacturer's instructions." There is no field inspection that clears a true sudden stoppage.

Sudden Reduction in Speed

"Sudden reduction in engine speed can occur when one or more of the propeller blades strike an object at a low engine rpm. After impact, the foreign object is cleared and the engine recovers rpm and continues to run unless stopped to prevent further damage." The handbook gives the taxi examples: "a raised section in the runway, a tool box, or a portion of another airplane," and adds the crucial qualifier: "When the accident occurs at high engine rpm, shocks are much more severe."

The Inspection Sequence

FAA-H-8083-32B lays out the procedure as a general rule, with the standing caveat that "you must comply with the manufacturer's information."

1. External inspection. "Make a thorough external inspection of the engine mount, crankcase, and nose section to determine whether any parts have been damaged. If damage is found that cannot be corrected by line maintenance, remove the engine. Internal components can be damaged, especially counter weights on the crankshaft."
2. Oil screens, filters, sump plugs, and drained oil. "Remove the engine oil screens or filters. Inspect them for the presence of metal particles. Remove the engine sump plugs, drain the oil into a clean container, strain it through a clean cloth, and check the cloth and the strained oil for metal particles."
3. The metal decision. "Heavy metal particles in the oil indicate a definite engine failure, and the engine must be removed. However, if the metal particles present are similar to fine filings, continue the inspection of the engine to determine its serviceability." And the warning that follows: "Metal in the screens is a sign that the bearings have been compromised and are in the process of failing."
4. Runout check. "Remove the propeller and check the crankshaft, or the propeller drive shaft on reduction-gear engines, for misalignment. Clamp a test indicator to the nose section of the engine. Use the dial-indicator that has 1/1,000-inch graduations. Remove the spark plugs from all the cylinders. Then, turn the crankshaft, and observe if the crankshaft, propeller shaft, or flange turns straight without any bending taking place." If runout at the front seal location exceeds the manufacturer's permissible limit, the engine is removed.
5. Blade track. If runout is within limits, "install a serviceable propeller. Make an additional check by tracking the propeller at the tip in the same plane, perpendicular to the axis of rotation, to assure that blade track tolerance is within the prescribed limits." This is the same 1/16-inch check covered in Section 7.2.
6. Ground run and re-check. "Start the engine to see if operation is smooth, without vibration, and the power output adequate. If the engine operates properly during this ground check, shut the engine down and repeat the inspection for metal particles in the oil system."

Note the structure: metal is checked twice — before and after the ground run. A shock-damaged bearing that is not yet shedding may begin shedding once it is loaded, so a single clean check at step 2 does not clear the engine.

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Metal in the Oil: Reading the Evidence

The handbook separates the analysis carefully, because a false positive costs an engine removal and a false negative costs an engine failure.

"Carbon tends to break loose from the interior of the engine in rock-like pieces that have the appearance of metal." The first test is therefore not how much but is it metal at all.

Ferrous versus non-ferrous. "Before removing an engine for suspected internal failure, as indicated by foreign material on the oil screens or oil sump plugs, determine if the foreign particles are ferrous metal by placing them close to a magnet to see if they are magnetic." The handbook then draws the line: "Any ferrous metal in the oil screens is cause for concern. Very small amounts of nonferrous metal, especially after major engine maintenance, can sometimes be normal."

The size and quantity test. "If only small particles are found that are similar in nature to filings, drain the oil system, and refill it. Then, ground-run the engine and reinspect the oil screens and magnetic chip detectors. If no further evidence of foreign material is found, continue the engine in service or per the manufacturer's instructions. However, engine performance should be closely observed for any indication of difficulty or internal failure."

Section 9.4 established how to sort the material itself: magnetic particles come from steel cylinder walls, rings, camshaft lobes, and lifters; non-magnetic particles come from aluminum pistons, bronze and copper bushings, and silver or babbitt bearings.

Spectrometric Oil Analysis (SOAP)

Special inspections catch events. Spectrometric oil analysis catches trends. FAA-H-8083-32B describes the Spectrometric Oil Analysis Engine Inspection Program as a program in which an oil sample is analyzed for the wear metals it carries in suspension, and notes that "the advantage of oil analysis is an increase in safety" through early detection. The parallel program on the turbine side is engine condition monitoring, where trended EGT, fuel flow, and spool speeds identify deterioration before it becomes a finding.

The key distinction for the exam: SOAP measures metal too fine to see on a screen or chip detector. It does not replace the screen and detector inspection; it detects the stage before them. A rising trend in a specific element points at a specific component family, which is why a SOAP report is read as a series, never as a single sample.

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Life-Limited Parts

The Definition and Why It Is Absolute

14 CFR § 43.10(a) defines the terms:

Life-limited part means any part for which a mandatory replacement limit is specified in the type design, the Instructions for Continued Airworthiness, or the maintenance manual.

Life status means the accumulated cycles, hours, or any other mandatory replacement limit of a life-limited part.

Two consequences follow directly:

1. A life limit is not an "on condition" judgment. A turbine disk at its cycle limit is removed whether or not it inspects perfectly, because the limit is set against a fatigue-life analysis, not against detectable damage. This is the opposite of the overhaul "Service Limits" logic of Section 15.2.
2. Cycles, not hours, are usually the counter on turbine rotating parts, because the damage mechanism is low-cycle fatigue driven by start-and-stop thermal and centrifugal loading. An engine flown on long sectors accumulates hours quickly and cycles slowly; an engine in circuit training does the reverse.

Disposition: The § 43.10 Control Requirement

Since April 15, 2002, "each person who removes a life-limited part from a type-certificated product must ensure that the part is controlled using one of the methods in this paragraph. The method must deter the installation of the part after it has reached its life limit." The four acceptable methods:

There is one exception, at § 43.10(b): temporary removal and reinstallation for the purpose of performing maintenance needs no disposition if the life status has not changed, the removal and reinstallation is on the same serial-numbered product, and that product does not accumulate time in service while the part is off.

Recordkeeping: § 91.417

The owner or operator must keep records containing "the current status of life-limited parts of each airframe, engine, propeller, rotor, and appliance" under 14 CFR § 91.417(a)(2)(ii). That record sits alongside the other four items in the same paragraph — total time in service, time since last overhaul of items overhauled on a specified time basis, current inspection status, and current AD status — and § 91.417(b)(2) requires those records to be retained and transferred with the aircraft when the aircraft is sold.

That transfer requirement is what makes a life-limited part's paperwork as valuable as the part. A turbine disk with unknown life status is scrap, regardless of its physical condition, because nothing can substantiate how many cycles remain. The technician's practical duty is therefore to record the life status at every removal, every time, in the method the operator's system uses — and to treat a missing entry as a discrepancy rather than an administrative loose end.

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Independent Prep Note

Independent FAA AMT Powerplant prep by OpenExamPrep. Not sponsored by or affiliated with the Federal Aviation Administration (FAA). Technical data compiled from FAA-H-8083-32B, FAA AC 43.13-1B, and 14 CFR Parts 43 and 65.