What does it mean if air escapes from the exhaust during a differential compression check?

It means the exhaust valve is not sealing. Air pumped into the cylinder near top dead center on the compression stroke is passing the exhaust valve seat and out through the exhaust stack. Before you condemn the cylinder, it is common practice to stake the valve and recheck, because carbon trapped on the seat can produce the same symptom and the valve may reseat.

Where is foreign object damage usually found on a turbine engine?

In the compressor, and usually in the first stages. Anything drawn through the inlet, whether ramp debris, hardware, ice, or birds, hits the inlet guide vanes and early compressor blades first, so that is where nicks, dents, and torn leading edges show up on an inlet or borescope inspection. Damage further aft normally came from a part that failed upstream of it.

Why are magnetic chip detectors installed in turbine engine lubrication systems?

They are magnets placed in the oil flow that capture ferrous particles shed by bearings, gears, and seals, so a technician can see wear evidence during scheduled checks. A trace of fine fuzz may be acceptable, while chips or flakes normally send you to the maintenance manual for a defined action such as oil analysis or a flush and recheck at a shortened interval.

What causes cracks and heat discoloration on combustion liners and nozzle vanes?

Localized overheating. Hot streaks form when fuel is not distributed evenly through the burner, most often because a fuel nozzle has a carboned or damaged spray pattern, and the liner or vane metal in that streak runs hotter than the material around it. Repeated heating and cooling of that spot produces the discoloration and the thermal cracks you find during hot-section inspection.

What does a light-colored streak at an exhaust slip joint indicate?

An exhaust gas leak. Escaping gas carries deposits that leave a gray or white trail downstream of the joint or clamp, and the escaping flow often scrubs that area unusually clean. Exhaust leaks are treated as urgent findings because they can feed carbon monoxide into cabin heat air and can direct hot gas onto nearby structure, wiring, or fuel and oil lines.

Local heat discoloration and small cracks found on turbine engine combustion liners and nozzle vanes are generally the result of

high operating temperatures and thermal stress

foreign object damage from ingested debris

corrosion from moisture in the fuel supply

Metal particles found on a reciprocating engine oil screen during inspection most likely indicate

internal engine wear or component failure

excessive fuel dilution of the engine oil

normal oil oxidation from extended operation

Magnetic chip detectors are installed in turbine engine lubrication systems to

capture ferrous particles for early wear detection

remove water that has condensed in the oil

regulate the oil pressure delivered to the bearings

During inspection of an exhaust system, a streak of light-colored deposit trailing from a slip joint or clamp most often indicates

an exhaust gas leak at that joint

normal heat oxidation of the metal

excessive lubrication of the clamp

Foreign object damage (FOD) on a turbine engine is most commonly found on the

compressor inlet blades and vanes

Where do stress-rupture cracks usually appear on a gas turbine engine's turbine blades?

Across the leading or trailing edge, at a right angle to the edge.

Along the leading edge, running parallel to the edge.

Across the blade root, parallel to the fir-tree serrations.

Hot-section inspections for many modern turbine engines are required

only at the time of engine overhaul.

only after an over-temperature or overspeed has occurred.

Bowing of turbine blades is an indication of what condition?

An under-temperature condition.

Necking and mottling of turbine blades are caused by

bending as the gas strikes the blades.

During engine overhaul inspection, ball or roller bearings are found to be magnetized but otherwise have no defects. They

must be degaussed before being returned to service.

must be scrapped and cannot be used again.

are in an acceptable condition and may be reused as is.

Engine vibration isolation mounts are installed to

prevent engine vibration loads from being transmitted to the airframe structure.

stop external vibrations from entering the engine in service.

damp vibration stresses while the engine is carried on a transport stand.

Following a hard landing, inspection of the engine mounting bolts shows that the bolt torque has decreased. The correct action is to

remove the bolt and inspect it, as it may have stretched due to the hard landing.

add washers to take up any gap or slackness and re-torque to the correct value.

re-torque the bolt to the correct torque value and return it to service.

The forward engine mount of a turbofan installation typically carries which loads?

Thrust, vertical, and shear loads.

Centrifugal, thrust, and axial loads.

Thrust, vertical, and impact loads.

The term "powerplant" refers to

the complete engine as installed on the aircraft, including all connections, controls, cowlings, and inlet.

the basic engine together with its electronic control unit only.

the basic engine plus the thrust reverser, exhaust, and accessory gearbox only.

Following a report of a hard landing, the first inspection action on the powerplant is to

carry out a complete visual examination of the powerplant.

examine the engine mounts and borescope the nozzle guide vanes and turbine.

examine the engine mounts and the mounting fuse pins.

During inspection, turbine engine components exposed to high temperatures may only be marked with materials approved by the manufacturer. These materials generally include

layout dye, an approved felt-tip marker, or chalk.

layout dye, an approved felt-tip marker, or a wax or grease pencil.

layout dye, an approved felt-tip marker, or a graphite lead pencil.

Foreign object damage on a turbine engine compressor, when borescope-inspected, is indicated by

nicks and scores on the blades.

Galling of a metal surface is a condition caused by excessive:

chafing between loaded surfaces.

If a turbine engine's coast-down (run-down) time is less than the minimum specified for that engine, it indicates that:

the rotating assembly is being restricted.

the main bearings are within normal wear limits.

the rotating assembly is free and serviceable.

A spectrometric oil analysis program (SOAP) is most effective when oil samples are taken:

at specified regular intervals.

A rotation (hand-cranking) pad provided on a turbine engine accessory drive gearbox is used to:

manually rotate the N2 spool for inspection.

drive the fuel control unit during ground runs.

mount an alternate tachometer generator.

To inhibit the fuel system of an installed turbine engine for preservation, the technician should

dry-motor the engine while feeding preservative fluid through the fuel system.

remove the igniter plugs and drain the fuel manifold completely.

pump engine oil into the fuel system while the engine is stationary.

When an engine is placed in storage, the purpose of the desiccant is to

absorb moisture from the air inside the sealed container.

neutralize acids formed by combustion residue.

act as a corrosion-inhibiting coating on the metal parts.

Engine Inspection — FAA A&P Test Questions (ACS AM.III.C)

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 July 27, 2026 · Last reviewed October 21, 2026

Written against the FAA primary sources cited at the foot of this page.

What ACS AM.III.C covers

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.

Where this sits on the test

ACS AM.III.C is tested on the FAA Powerplant written test, one of 1,353 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.

FAA handbook references

FAA-H-8083-32

Three traps candidates fall into

On the differential compression test, candidates flip the exhaust and intake answers. Air heard at the exhaust tailpipe means the exhaust valve is not sealing, not the intake valve. Air at the carburetor or air inlet is the intake valve, and air at the crankcase breather is rings or cylinder walls.
Any metal on the oil screen gets read as a scrapped engine. The FAA expects you to identify the material first: fine gray fuzz can reflect normal wear, while flakes of bearing material or steel chips point to one specific failing component and to a specific limit in the maintenance manual.
Blade damage terms get used interchangeably. A nick is a sharp, V-shaped depression in the edge, a dent is a rounded surface depression, and a gouge scoops material out with a wide, rough cut. Manufacturers publish different blend limits for each, so the wrong word produces the wrong repair answer.

35 free sample questions from ACS AM.III.C

AM.III.CTap an answer
While performing a differential compression test, air is heard escaping from the engine exhaust outlet. This indicates a leaking
Show the answer and explanation
Answer: exhaust valve
Why: 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.· FAA-H-8083-32 — Cylinder leakage diagnosis during compression testing
AM.III.CTap an answer
Local heat discoloration and small cracks found on turbine engine combustion liners and nozzle vanes are generally the result of
Show the answer and explanation
Answer: high operating temperatures and thermal stress
Why: 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.· FAA-H-8083-32 — Turbine hot-section inspection
AM.III.CTap an answer
A defect described as a sharp, V-shaped depression in the edge of a turbine compressor blade is properly called a
Show the answer and explanation
Answer: nick
Why: 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.· FAA-H-8083-32 — Turbine blade defect definitions
AM.III.CTap an answer
Metal particles found on a reciprocating engine oil screen during inspection most likely indicate
Show the answer and explanation
Answer: internal engine wear or component failure
Why: 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.· FAA-H-8083-32 — Engine inspection / oil screen and filter inspection
AM.III.CTap an answer
Magnetic chip detectors are installed in turbine engine lubrication systems to
Show the answer and explanation
Answer: capture ferrous particles for early wear detection
Why: 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.· FAA-H-8083-32 — Turbine engine inspection / magnetic chip detectors
AM.III.CTap an answer
During inspection of an exhaust system, a streak of light-colored deposit trailing from a slip joint or clamp most often indicates
Show the answer and explanation
Answer: an exhaust gas leak at that joint
Why: 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.· FAA-H-8083-32 — Exhaust system inspection
AM.III.CTap an answer
When inspecting reciprocating engine cylinder hold-down nuts and through-bolts, the technician should primarily check for
Show the answer and explanation
Answer: proper torque and security
Why: 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.· FAA-H-8083-32 — Cylinder and hold-down hardware inspection
AM.III.CTap an answer
Foreign object damage (FOD) on a turbine engine is most commonly found on the
Show the answer and explanation
Answer: compressor inlet blades and vanes
Why: 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.· FAA-H-8083-32 — Turbine engine inspection / foreign object damage
AM.III.CTap an answer
Where do stress-rupture cracks usually appear on a gas turbine engine's turbine blades?
Show the answer and explanation
Answer: Across the leading or trailing edge, at a right angle to the edge.
Why: 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.· FAA-H-8083-32 — Engine Inspection
AM.III.CTap an answer
Hot-section inspections for many modern turbine engines are required
Show the answer and explanation
Answer: on a time or cycle basis.
Why: 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.· FAA-H-8083-32 — Engine Inspection
AM.III.CTap an answer
Which of the following conditions is usually not acceptable to any extent in turbine blades?
Show the answer and explanation
Answer: Cracks of any length.
Why: 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.· FAA-H-8083-32 — Engine Inspection
AM.III.CTap an answer
During a borescope inspection of turbine blades, which condition indicates an actual or impending blade failure?
Show the answer and explanation
Answer: Tip curl of the blade.
Why: 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.· FAA-H-8083-32 — Engine Inspection
AM.III.CTap an answer
Bowing of turbine blades is an indication of what condition?
Show the answer and explanation
Answer: An over-temperature condition.
Why: 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.· FAA-H-8083-32 — Engine Inspection
AM.III.CTap an answer
Which of the following defects is most likely to occur in the turbine section of a gas turbine engine?
Show the answer and explanation
Answer: Cracking.
Why: 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.· FAA-H-8083-32 — Engine Inspection
AM.III.CTap an answer
Necking and mottling of turbine blades are caused by
Show the answer and explanation
Answer: thermal stress in service.
Why: 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.· FAA-H-8083-32 — Engine Inspection
AM.III.CTap an answer
During engine overhaul inspection, ball or roller bearings are found to be magnetized but otherwise have no defects. They
Show the answer and explanation
Answer: must be degaussed before being returned to service.
Why: 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).· FAA-H-8083-32 — Engine Inspection
AM.III.CTap an answer
Indentations in a bearing race caused by high static or shock loads pressing the rolling elements into the raceway are known as
Show the answer and explanation
Answer: brinelling.
Why: 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).· FAA-H-8083-32 — Engine Inspection
AM.III.CTap an answer
Engine vibration isolation mounts are installed to
Show the answer and explanation
Answer: prevent engine vibration loads from being transmitted to the airframe structure.
Why: 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.· FAA-H-8083-32 — Engine Inspection
AM.III.CTap an answer
Following a hard landing, inspection of the engine mounting bolts shows that the bolt torque has decreased. The correct action is to
Show the answer and explanation
Answer: remove the bolt and inspect it, as it may have stretched due to the hard landing.
Why: 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.· FAA-H-8083-32 — Engine Inspection
AM.III.CTap an answer
The forward engine mount of a turbofan installation typically carries which loads?
Show the answer and explanation
Answer: Thrust, vertical, and shear loads.
Why: 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.· FAA-H-8083-32 — Engine Inspection
AM.III.CTap an answer
Highly loaded forward engine mounts are most commonly manufactured as
Show the answer and explanation
Answer: forgings.
Why: 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.· FAA-H-8083-32 — Engine Inspection
AM.III.CTap an answer
Rigid pipework routed around a turbine engine is generally manufactured from
Show the answer and explanation
Answer: stainless steel.
Why: 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.· FAA-H-8083-32 — Engine Inspection
AM.III.CTap an answer
The term "powerplant" refers to
Show the answer and explanation
Answer: the complete engine as installed on the aircraft, including all connections, controls, cowlings, and inlet.
Why: 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.· FAA-H-8083-32 — Engine Inspection
AM.III.CTap an answer
Following a report of a hard landing, the first inspection action on the powerplant is to
Show the answer and explanation
Answer: carry out a complete visual examination of the powerplant.
Why: 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.· FAA-H-8083-32 — Engine Inspection
AM.III.CTap an answer
During inspection, turbine engine components exposed to high temperatures may only be marked with materials approved by the manufacturer. These materials generally include
Show the answer and explanation
Answer: layout dye, an approved felt-tip marker, or chalk.
Why: 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.· FAA-H-8083-32 — Engine Inspection
AM.III.CTap an answer
When the leading edge of a first-stage turbine blade is found to have stress-rupture cracks, which of the following should be suspected?
Show the answer and explanation
Answer: An over-temperature condition.
Why: 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.· FAA-H-8083-32 — Engine Inspection
AM.III.CTap an answer
Foreign object damage on a turbine engine compressor, when borescope-inspected, is indicated by
Show the answer and explanation
Answer: nicks and scores on the blades.
Why: 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.· FAA-H-8083-32 — Engine Inspection
AM.III.CTap an answer
Cracks may develop in hot-section components of a turbine engine if, during inspection, they are marked with
Show the answer and explanation
Answer: a lead (graphite) pencil.
Why: 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.· FAA-H-8083-32 — Engine Inspection
AM.III.CTap an answer
Galling of a metal surface is a condition caused by excessive:
Show the answer and explanation
Answer: chafing between loaded surfaces.
Why: 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.· FAA-H-8083-32 — Engine Inspection
AM.III.CTap an answer
If a turbine engine's coast-down (run-down) time is less than the minimum specified for that engine, it indicates that:
Show the answer and explanation
Answer: the rotating assembly is being restricted.
Why: 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.· FAA-H-8083-32 — Engine Inspection
AM.III.CTap an answer
A spectrometric oil analysis program (SOAP) is most effective when oil samples are taken:
Show the answer and explanation
Answer: at specified regular intervals.
Why: 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.· FAA-H-8083-32 — Engine Inspection
AM.III.CTap an answer
Dynamic balancing of a turbine engine rotor corrects unbalance in:
Show the answer and explanation
Answer: two planes.
Why: 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.· FAA-H-8083-32 — Engine Inspection
AM.III.CTap an answer
A rotation (hand-cranking) pad provided on a turbine engine accessory drive gearbox is used to:
Show the answer and explanation
Answer: manually rotate the N2 spool for inspection.
Why: 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.· FAA-H-8083-32 — Engine Inspection
AM.III.CTap an answer
To inhibit the fuel system of an installed turbine engine for preservation, the technician should
Show the answer and explanation
Answer: dry-motor the engine while feeding preservative fluid through the fuel system.
Why: 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.· FAA-H-8083-32 — Engine Inspection
AM.III.CTap an answer
When an engine is placed in storage, the purpose of the desiccant is to
Show the answer and explanation
Answer: absorb moisture from the air inside the sealed container.
Why: 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.· FAA-H-8083-32 — Engine Inspection

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Related subject areas

The areas that share the most ground with AM.III.C — study them alongside it.

Inspection Concepts and Techniques (AM.I.K)
Airframe Inspection (AM.II.D)
Reciprocating Engines (AM.III.A)
Turbine Engines (AM.III.B)

Frequently asked questions

What does it mean if air escapes from the exhaust during a differential compression check?: It means the exhaust valve is not sealing. Air pumped into the cylinder near top dead center on the compression stroke is passing the exhaust valve seat and out through the exhaust stack. Before you condemn the cylinder, it is common practice to stake the valve and recheck, because carbon trapped on the seat can produce the same symptom and the valve may reseat.
Where is foreign object damage usually found on a turbine engine?: In the compressor, and usually in the first stages. Anything drawn through the inlet, whether ramp debris, hardware, ice, or birds, hits the inlet guide vanes and early compressor blades first, so that is where nicks, dents, and torn leading edges show up on an inlet or borescope inspection. Damage further aft normally came from a part that failed upstream of it.
Why are magnetic chip detectors installed in turbine engine lubrication systems?: They are magnets placed in the oil flow that capture ferrous particles shed by bearings, gears, and seals, so a technician can see wear evidence during scheduled checks. A trace of fine fuzz may be acceptable, while chips or flakes normally send you to the maintenance manual for a defined action such as oil analysis or a flush and recheck at a shortened interval.
What causes cracks and heat discoloration on combustion liners and nozzle vanes?: Localized overheating. Hot streaks form when fuel is not distributed evenly through the burner, most often because a fuel nozzle has a carboned or damaged spray pattern, and the liner or vane metal in that streak runs hotter than the material around it. Repeated heating and cooling of that spot produces the discoloration and the thermal cracks you find during hot-section inspection.
What does a light-colored streak at an exhaust slip joint indicate?: An exhaust gas leak. Escaping gas carries deposits that leave a gray or white trail downstream of the joint or clamp, and the escaping flow often scrubs that area unusually clean. Exhaust leaks are treated as urgent findings because they can feed carbon monoxide into cabin heat air and can direct hot gas onto nearby structure, wiring, or fuel and oil lines.

All 40 ACS areas

General

Airframe

Powerplant

Primary sources

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