Engine Inspection is the powerplant subject area that asks whether you can look at an engine and tell what the evidence in front of you means. AM.III.C questions put you at a compression gauge, an oil screen, a cracked combustor liner, or a stained exhaust clamp and ask what condition produced what you see. The FAA is not checking whether you can recite an inspection interval here; it is checking whether you can read damage. Expect reciprocating and turbine hardware mixed together in the same block of questions.
Written by the AMTprep editorial team · Published · Last reviewed
Written against the FAA primary sources cited at the foot of this page.
This area covers routine and troubleshooting inspection of both reciprocating and turbine engines, and the technical detail comes straight out of the Powerplant Handbook, FAA-H-8083-32. On the reciprocating side, the differential compression test appears in nearly every form: where you hear the escaping air tells you which component is leaking. Air at the exhaust stack points to an exhaust valve, air at the carburetor or induction inlet points to an intake valve, and air at the crankcase breather or oil filler points to worn rings or a scored cylinder wall. You will also see oil screen and filter inspection, where metal found in the screen is a symptom you must identify by type and quantity rather than a simple pass or fail, and cylinder hold-down hardware, where you are checking through-bolts and hold-down nuts for looseness and correct torque rather than for cosmetic condition. On the turbine side the questions shift to damage vocabulary and hot-section evidence. You are expected to know the standard defect names, because repair and blend limits in the manual are written against those exact words: a nick is a sharp, V-shaped depression in a blade edge, distinct from a dent, a gouge, or a score. Discoloration and cracking on combustion liners and nozzle vanes trace back to localized hot spots, most often caused by a fuel nozzle that is no longer spraying an even pattern. Foreign object damage is expected in the compressor, where anything drawn through the inlet strikes first. Magnetic chip detectors round out the lubrication questions, collecting ferrous particles so wear is found before a bearing fails. Exhaust system inspection closes the area: a light-colored deposit trailing from a slip joint or clamp is the classic sign of a gas leak, and exhaust leaks are urgent because of carbon monoxide and fire risk, not noise.
ACS AM.III.C is tested on the FAA Powerplant written test, one of 1,355 ACS-tagged questions in the Powerplant bank. Every question tagged to this area carries a worked rationale and its FAA handbook reference, so you can drill the code itself rather than the whole test.
While performing a differential compression test, air is heard escaping from the engine exhaust outlet. This indicates a leaking
Local heat discoloration and small cracks found on turbine engine combustion liners and nozzle vanes are generally the result of
A defect described as a sharp, V-shaped depression in the edge of a turbine compressor blade is properly called a
Metal particles found on a reciprocating engine oil screen during inspection most likely indicate
Magnetic chip detectors are installed in turbine engine lubrication systems to
During inspection of an exhaust system, a streak of light-colored deposit trailing from a slip joint or clamp most often indicates
When inspecting reciprocating engine cylinder hold-down nuts and through-bolts, the technician should primarily check for
Foreign object damage (FOD) on a turbine engine is most commonly found on the
Where do stress-rupture cracks usually appear on a gas turbine engine's turbine blades?
Hot-section inspections for many modern turbine engines are required
Which of the following conditions is usually not acceptable to any extent in turbine blades?
During a borescope inspection of turbine blades, which condition indicates an actual or impending blade failure?
Bowing of turbine blades is an indication of what condition?
Which of the following defects is most likely to occur in the turbine section of a gas turbine engine?
Necking and mottling of turbine blades are caused by
During engine overhaul inspection, ball or roller bearings are found to be magnetized but otherwise have no defects. They
Indentations in a bearing race caused by high static or shock loads pressing the rolling elements into the raceway are known as
Engine vibration isolation mounts are installed to
Following a hard landing, inspection of the engine mounting bolts shows that the bolt torque has decreased. The correct action is to
The forward engine mount of a turbofan installation typically carries which loads?
Highly loaded forward engine mounts are most commonly manufactured as
Rigid pipework routed around a turbine engine is generally manufactured from
The term "powerplant" refers to
Following a report of a hard landing, the first inspection action on the powerplant is to
During inspection, turbine engine components exposed to high temperatures may only be marked with materials approved by the manufacturer. These materials generally include
When the leading edge of a first-stage turbine blade is found to have stress-rupture cracks, which of the following should be suspected?
Foreign object damage on a turbine engine compressor, when borescope-inspected, is indicated by
Cracks may develop in hot-section components of a turbine engine if, during inspection, they are marked with
Galling of a metal surface is a condition caused by excessive:
If a turbine engine's coast-down (run-down) time is less than the minimum specified for that engine, it indicates that:
A spectrometric oil analysis program (SOAP) is most effective when oil samples are taken:
Dynamic balancing of a turbine engine rotor corrects unbalance in:
A rotation (hand-cranking) pad provided on a turbine engine accessory drive gearbox is used to:
To inhibit the fuel system of an installed turbine engine for preservation, the technician should
When an engine is placed in storage, the purpose of the desiccant is to
ACS code: AM.III.C
Correct answer: exhaust valve
Rationale: Air heard at the exhaust outlet means it is leaking past the exhaust valve. Air at the carburetor/intake indicates an intake valve leak, and air at the crankcase breather indicates worn or broken piston rings. Listening for the escape point localizes the leak during inspection.
ACS code: AM.III.C
Correct answer: high operating temperatures and thermal stress
Rationale: Combustion liners and turbine nozzle vanes operate in the hottest gas path. Repeated heating and cooling produces thermal stress that leads to localized discoloration, warping, and cracking. FOD typically dents or nicks compressor blades, and fuel-borne moisture is not the usual cause of hot-section cracking.
ACS code: AM.III.C
Correct answer: nick
Rationale: Standardized inspection terminology defines a nick as a sharp, V-shaped depression in an edge or surface, typically caused by foreign objects. A score is a deeper scratch from a harder material, and a pit is a small, rounded cavity often from corrosion. Using correct terms ensures accurate defect reporting.
ACS code: AM.III.C
Correct answer: internal engine wear or component failure
Rationale: The oil screen and filter trap particles circulating in the oil. Metal contamination signals abnormal internal wear or impending failure of bearings, gears, or other components, and must be investigated. Oil oxidation produces sludge or varnish, and fuel dilution thins the oil rather than introducing metal.
ACS code: AM.III.C
Correct answer: capture ferrous particles for early wear detection
Rationale: A magnetic chip detector uses a magnet to collect ferrous debris from the oil so technicians can detect internal wear before it becomes a failure. It performs an inspection/monitoring function and does not regulate oil pressure or separate water from the oil.
ACS code: AM.III.C
Correct answer: an exhaust gas leak at that joint
Rationale: Escaping hot exhaust gas leaves a tell-tale light-gray or sooty streak downstream of the leak point, signaling a faulty joint, clamp, or crack that must be corrected. General heat oxidation discolors the whole surface uniformly, and exhaust clamps are not lubricated, so a streak points to a leak.
ACS code: AM.III.C
Correct answer: proper torque and security
Rationale: Cylinder hold-down hardware must remain at the specified torque to keep the cylinder properly seated and sealed; inspection verifies torque and security per the manufacturer's data. Paint color and serial-number matching are not the function of hold-down fasteners, so torque and security are the key checks.
ACS code: AM.III.C
Correct answer: compressor inlet blades and vanes
Rationale: FOD occurs when ingested debris strikes engine components; the first parts in the gas path, the compressor inlet blades and vanes, are most exposed and therefore most frequently damaged. The rear turbine bearing and accessory gearbox are not in the direct ingestion path, so inspectors focus first on the inlet area.
ACS code: AM.III.C
Correct answer: Across the leading or trailing edge, at a right angle to the edge.
Rationale: Stress-rupture cracks from sustained high temperature and centrifugal load typically appear as fine cracks running across the leading or trailing edge, at right angles to that edge. Recognizing this characteristic orientation distinguishes genuine stress-rupture damage from surface marks during inspection.
ACS code: AM.III.C
Correct answer: on a time or cycle basis.
Rationale: Per FAA-H-8083-32, hot-section components age mainly through accumulated running hours and thermal cycles, so modern engines schedule hot-section inspections on a time-in-service or cycle basis to catch creep, cracking, and distortion before failure. Inspecting only after an over-temperature event or solely at overhaul would let progressive heat damage go undetected.
ACS code: AM.III.C
Correct answer: Cracks of any length.
Rationale: Per FAA-H-8083-32, cracks in a turbine blade are stress raisers that can propagate rapidly under the high thermal and centrifugal loads and lead to blade liberation, so they are generally not acceptable to any extent. Minor dents and pits may be tolerated within defined limits because they do not concentrate stress as severely; a crack is cause for rejection.
ACS code: AM.III.C
Correct answer: Tip curl of the blade.
Rationale: Tip curl, where the trailing edge or tip of a blade bends over, results from creep and severe over-temperature and signals an actual or impending blade failure. Light speckling or surface color changes are common deposit or oxidation indications and are not by themselves evidence of failure.
ACS code: AM.III.C
Correct answer: An over-temperature condition.
Rationale: Bowing or bending of turbine blades is a classic sign of an over-temperature event: at excessive gas temperatures the blade material weakens and the gas-bending and centrifugal loads distort the airfoil. It is not caused by over-speed alone or by running too cool.
ACS code: AM.III.C
Correct answer: Cracking.
Rationale: The turbine section operates at very high temperature with large thermal-cycling and centrifugal stresses, so cracking of blades, vanes, and disks is the most likely defect found there. Pitting and galling are associated with corrosion and rubbing contact rather than the hot, highly stressed turbine.
ACS code: AM.III.C
Correct answer: thermal stress in service.
Rationale: Necking (local thinning) and mottling of turbine blades are produced by thermal stress, where repeated heating and cooling and over-temperature degrade the surface and material. They are service-induced defects, not manufacturing features or simple gas-bending damage.
ACS code: AM.III.C
Correct answer: must be degaussed before being returned to service.
Rationale: Magnetism in a bearing attracts and holds fine ferrous debris and can interfere with magnetic chip detectors, accelerating wear. If the bearing is otherwise serviceable it is not scrapped but must be degaussed (demagnetized) before being returned to service (FAA-H-8083-32, Engine Inspection).
ACS code: AM.III.C
Correct answer: brinelling.
Rationale: Brinelling is the formation of indentations in a bearing race when high static or shock loads press the balls or rollers into the raceway surface. Fretting and galling describe different rubbing or surface-transfer damage, so the static-load indentation pattern is correctly termed brinelling (FAA-H-8083-32, Engine Inspection).
ACS code: AM.III.C
Correct answer: prevent engine vibration loads from being transmitted to the airframe structure.
Rationale: Vibration-isolation mounts isolate the engine from the airframe so that engine-generated vibration is not transmitted into the aircraft structure, reducing fatigue and crew and passenger discomfort. They do not stop vibration from entering the engine, and their purpose is in-service isolation rather than protection on a transport stand.
ACS code: AM.III.C
Correct answer: remove the bolt and inspect it, as it may have stretched due to the hard landing.
Rationale: A drop in mounting-bolt torque after a hard landing can mean the bolt has stretched (yielded) under overload, so the correct action is to remove and inspect it rather than simply re-torque it. Adding washers or just re-torquing would mask a possibly stretched, weakened bolt and is unsafe.
ACS code: AM.III.C
Correct answer: Thrust, vertical, and shear loads.
Rationale: The forward engine mount typically carries engine thrust together with vertical (weight) and side or shear loads, transferring them into the pylon. Terms such as centrifugal and impact do not describe the steady mounting loads, so options using them are incorrect.
ACS code: AM.III.C
Correct answer: forgings.
Rationale: Highly loaded forward engine mounts are made as forgings because the forged grain flow gives the strength and fatigue resistance needed to carry thrust and vertical loads. Castings and fabricated sheet steel lack the consistent strength required for this critical structural fitting.
ACS code: AM.III.C
Correct answer: stainless steel.
Rationale: Pipework around an engine is generally stainless steel because it must resist the high temperatures, vibration, and corrosive environment of the engine bay. Aluminum would not withstand the heat, and plain mild steel would corrode, so stainless steel is the standard choice.
ACS code: AM.III.C
Correct answer: the complete engine as installed on the aircraft, including all connections, controls, cowlings, and inlet.
Rationale: A powerplant is the complete installed engine package: the basic engine plus all of its connections, controls, cowlings, inlet, and exhaust as fitted to the aircraft. Listing only the engine with a control unit, or only certain accessories, describes part of the installation rather than the whole powerplant.
ACS code: AM.III.C
Correct answer: carry out a complete visual examination of the powerplant.
Rationale: A reported hard landing first calls for a complete visual examination of the entire powerplant to find any obvious distortion or damage before deciding on deeper checks. Going straight to a borescope or mount-pin inspection skips the initial overall assessment the maintenance manual requires.
ACS code: AM.III.C
Correct answer: layout dye, an approved felt-tip marker, or chalk.
Rationale: Per FAA-H-8083-32, only marking materials free of harmful elements may be used on hot-section parts; approved materials generally include layout dye, approved felt-tip markers, and chalk. Wax or grease pencils and graphite (lead) pencils leave carbon, sulfur, or metallic deposits that, when heated, cause intergranular attack and cracking, so they are prohibited on high-temperature components.
ACS code: AM.III.C
Correct answer: An over-temperature condition.
Rationale: Per FAA-H-8083-32, stress-rupture cracks, which typically run across the leading edge of a first-stage turbine blade, are caused by prolonged operation at temperatures above limits combined with centrifugal stress. They are a classic over-temperature indication; a cooling-shield fault or overspeed produce different damage patterns rather than this characteristic stress-rupture cracking.
ACS code: AM.III.C
Correct answer: nicks and scores on the blades.
Rationale: Per FAA-H-8083-32, foreign object damage to compressor blades appears on borescope inspection as nicks, dents, and scores along the leading edges and faces where debris has struck the metal. Tip curl and flats describe rub or wear patterns from other causes, so the hallmark of FOD is the localized nicks and scores.
ACS code: AM.III.C
Correct answer: a lead (graphite) pencil.
Rationale: Marking hot-section components with a graphite (lead) pencil deposits carbon that, at high temperature, diffuses into the metal grain boundaries and causes intergranular cracking. Approved markers such as chalk and layout dye are free of such harmful deposits, so a lead pencil is the prohibited marking material.
ACS code: AM.III.C
Correct answer: chafing between loaded surfaces.
Rationale: Galling is surface damage in which excessive rubbing or chafing between two loaded metal surfaces generates local friction welding, so material tears and transfers from one part to the other. It results from excessive chafing under load rather than from scoring debris or temperature alone.
ACS code: AM.III.C
Correct answer: the rotating assembly is being restricted.
Rationale: A shorter-than-minimum coast-down time means the rotor is stopping too quickly, indicating added friction restricting the rotating assembly, typically from bearing distress or internal rubbing. A free assembly coasts for at least the minimum time, so a low value signals a restriction that must be investigated.
ACS code: AM.III.C
Correct answer: at specified regular intervals.
Rationale: Under a spectrometric oil analysis program, samples are drawn at specified regular intervals so the wear-metal trend can be compared consistently over time and developing faults detected. Sampling only when the tank is full or the oil is warm would yield irregular, non-comparable data unsuitable for trend monitoring.
ACS code: AM.III.C
Correct answer: two planes.
Rationale: Dynamic balancing detects and corrects unbalance in two planes, allowing both static (single-plane) and couple unbalance of a long rotor to be resolved. Static balancing alone addresses only a single plane, so a rotating assembly such as a turbine spool requires two-plane dynamic balancing for true smoothness.
ACS code: AM.III.C
Correct answer: manually rotate the N2 spool for inspection.
Rationale: The rotation pad on the accessory drive gearbox provides a drive point for hand-turning the engine high-pressure (N2) spool, allowing the compressor and turbine to be rotated for blade and borescope inspections. It is not provided for fitting a tachometer generator.
ACS code: AM.III.C
Correct answer: dry-motor the engine while feeding preservative fluid through the fuel system.
Rationale: The fuel system of an installed engine is preserved by dry-motoring the engine, in which the starter rotates the engine with the ignition off while preservative fluid is fed through the system to coat the pumps and lines. Simply pumping oil into a stationary engine would not circulate preservative through all of the fuel passages.
ACS code: AM.III.C
Correct answer: absorb moisture from the air inside the sealed container.
Rationale: Desiccant is a hygroscopic material packed inside the sealed storage container to absorb moisture from the trapped air, keeping the internal environment dry and preventing corrosion. It is not a corrosion-inhibiting coating; it functions only by drawing in water vapor.
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