FAA Aviation Mechanic Powerplant (AMP) flashcards

Aviation gasoline grades are dyed different colors to allow quick visual identification and prevent misfueling.

• 100LL avgas = blue
• Jet A/A-1 = clear to straw colored
• Color coding is a critical safety check before fueling
• Misfueling a piston engine with jet fuel can cause catastrophic failure

Memory trick: Blue Bird flies on 100LL, Jet flies clear as glass

An oil system design using a separate external oil tank rather than the engine crankcase, with a scavenge pump returning oil from the sump to the tank, offering better performance during extreme attitudes.

• Oil stored in external tank, not crankcase
• Requires both pressure pump and scavenge pump
• Better suited to aerobatic/extreme attitude operations
• Common in radial and some turbine engines

Memory trick: Dry sump keeps oil in its own tank, so flips and dives don't starve the pump

The number of degrees the magnet rotor turns past the neutral position before the breaker points open, chosen to coincide with maximum rate of change of magnetic flux for peak voltage output.

• Specified by the magneto manufacturer
• Set during internal timing before magneto installation
• Ensures the hottest possible spark at points opening

Memory trick: E-gap = 'Extra degrees past neutral for Extra voltage'

Avgas is standardly calculated at 6 pounds per gallon for weight and balance purposes.

• Avgas density: 6 lb/gallon (standard)
• Jet fuel density: approximately 6.7-7 lb/gallon depending on type
• Fuel weight = gallons × pounds per gallon

Memory trick: Six pounds a gallon keeps avgas math simple

When RPM exceeds the set value, the governor drains oil from the propeller hub, allowing blade angle to increase and RPM to decrease.

• Overspeed: oil drains, blade angle increases
• Underspeed: oil increases, blade angle decreases
• On-speed: pilot valve neutral, no oil flow change

Memory trick: Over means Out (oil out, blade opens up)

Dry, black, sooty deposits on spark plug electrodes caused by an excessively rich mixture, especially during extended idling.

• Most common at idle/low power with rich mixtures.
• Deposits are dry black soot, unlike the oily deposits of oil fouling.
• Can often be cleared by leaning and running the engine at higher power.

Memory trick: Carbon is Coal-black from a Choked-rich idle.

A positive-displacement pump using two meshing gears to move oil at a rate proportional to engine speed, supplying pressurized oil to the lubrication system.

• Positive displacement delivers consistent volume per revolution
• Paired with a pressure relief valve to prevent excess pressure
• Driven directly by the engine accessory section

Memory trick: 'Gears grab oil and shove it through'

A nozzle that decreases in cross-sectional area toward the exit, accelerating subsonic exhaust gas while reducing static pressure.

• Used on most subsonic turbofans
• Converts pressure energy to velocity
• Divergent sections needed for supersonic acceleration
• Nozzle shape affects thrust efficiency

Memory trick: Convergent = squeeze to speed up, like pinching a hose

An additive (EGME, trade name Prist) added to turbine fuel to prevent ice crystal formation from entrained water at low temperatures.

• Prevents water from freezing and clogging fuel filters
• Common in turbine fuel operations, especially at altitude
• Also has some biocidal properties against microbial growth

Memory trick: FSII freezes out the freeze (prevents ice)

The distributor block routes high-voltage pulses to spark plugs in the exact sequence of the engine's firing order; each numbered terminal corresponds to a specific cylinder's ignition event.

• Distributor rotor passes each terminal in the same sequence as the engine's firing order
• Ignition harness leads must be traced and connected to match this sequence
• Mismatched leads cause rough running, backfiring, or a no-start condition

Memory trick: Wrong wire, wrong turn — cylinders fire out of order and the engine coughs.

Carbon brushes in a starter-generator must be measured against a minimum length specified by the manufacturer; brushes below this limit are replaced to avoid arcing and poor contact.

• Minimum brush length is specified in the component maintenance manual
• Worn brushes reduce spring pressure, causing arcing and overheating
• Brush sets are typically replaced together, not individually

Memory trick: A short brush can't reach — replace before it fails to make contact

The breaker point gap sets the exact instant the points open relative to the rotating magnet, which must coincide with the E-gap position for maximum induced voltage.

• Set with a feeler gauge at maximum opening
• Too narrow = retarded timing (late opening)
• Too wide = advanced timing (early opening)
• Must align with E-gap for peak spark energy

Memory trick: Narrow gap = Nap late (retard); Wide gap = 'Way early' (advance).

Deposits of lead compounds from leaded avgas that accumulate on spark plug electrodes during rich, low-power operation, causing rough running or magneto drop that can often be cleared by leaning and increasing power.

• Common during prolonged ground idle/taxi
• Cleared by leaning mixture and brief high power
• Chronic fouling requires spark plug cleaning/replacement

Memory trick: Lead builds up like soot on a candle wick—burn it off by leaning and revving.

A combustion chamber design using one continuous liner surrounding the turbine shaft, providing even temperature distribution and reduced weight.

• Used in most modern turbofan engines
• Single continuous liner around the shaft
• Lighter and shorter than can or can-annular types

Memory trick: CAN, CAN-ANNULAR, ANNULAR — think 'Cans get Annular over time' as engines evolved.

The two crankcase halves of a horizontally opposed engine are bolted together and line-bored as a single unit, so their main bearing and cam bores align only with each other and cannot be individually interchanged.

• Line-bored together after assembly
• Must be replaced/repaired as a matched pair
• Individual interchange can cause bearing misalignment

Memory trick: Crankcase halves are like two puzzle pieces cut together—swap only one and nothing fits.

Operating the fuel/air mixture richer than chemically correct (stoichiometric) to lower combustion temperatures and achieve maximum engine power, typically around 12:1.

• Stoichiometric ratio is approximately 15:1 by weight
• Best power mixture is enriched to roughly 12:1
• Excess fuel evaporates and absorbs heat, cooling the cylinders and reducing detonation risk

Memory trick: Extra fuel acts like a coolant blanket, letting the engine push harder.

Methods used to keep turbine blades below their material limits despite exposure to extremely hot combustion gases, including convection, impingement, and film cooling.

• Convection: air flows through internal blade passages
• Impingement: air jets strike internal blade walls
• Film: air exits surface holes forming a cooling film

Memory trick: 'Film wraps a blanket over the blade' - film cooling forms a surface layer

A propeller balance check performed at rest using knife-edges to verify even weight distribution around the hub axis.

• Performed with the propeller not rotating
• Checks for heavy spots that cause the assembly to rotate
• Dynamic balance requires spinning and specialized equipment

Memory trick: Static sits still on the knife edge

A gas turbine engine with a large front fan that bypasses a portion of intake air around the engine core, generating most thrust from the bypass airflow.

• Improves fuel efficiency over turbojets
• Bypass ratio compares bypass air to core air
• Common on commercial airliners

Memory trick: 'Jets Fan Props Shafts' - Turbojet, Turbofan, Turboprop, Turboshaft

Adjustable compressor stator vanes that change angle with engine speed to maintain proper airflow angle into rotor blades, preventing compressor stall.

• Controlled by fuel control/FADEC based on N2 speed and temperature
• Work with bleed valves and multi-spool design to prevent stall
• Most critical at low engine speeds/high angles of attack

Memory trick: 'VSV Vanes Steer the Vortex' — angling airflow to keep it smooth.

A high-energy capacitor discharge unit that stores electrical energy and releases it in a very hot, intense spark across turbine igniter plugs for reliable ignition of jet fuel.

• Produces very high voltage, short-duration sparks
• Only 1-2 igniters needed per engine (unlike many spark plugs on recip engines)
• Required because jet fuel is less volatile than avgas

Memory trick: CD exciter = 'Capacitor Charges then blasts a Hot spark' for stubborn jet fuel

A component in continuous-flow fuel injection systems that equally distributes metered fuel from the fuel control unit to each cylinder's injector line.

• Mounted centrally, typically atop the engine
• Contains a diaphragm/spring valve for equal distribution
• Shuts off fuel uniformly to all cylinders when engine stops

Memory trick: The flow DIVIDER splits fuel like slicing a pie equally for every cylinder.

Perforated honeycomb panels lining the fan inlet and duct that absorb sound energy to reduce turbofan engine noise.

• Targets fan noise, the dominant noise source in high-bypass engines
• Consists of a perforated facesheet over honeycomb core
• Helps meet FAA/ICAO noise certification standards

Memory trick: Honeycomb panels are noise 'sponges' soaking up fan racket.

A functional test comparing a resistance temperature sensor's measured ohmic value at a known temperature against a manufacturer's resistance-temperature chart.

• Resistance changes proportionally with temperature
• Checked with an ohmmeter at a known ambient temperature
• Different from thermocouple-type probes which measure millivolt output

Memory trick: Resistance rises and falls with heat — match it to the chart to seal the deal.

A system that directs fan or compressor bleed air onto the turbine case to control its thermal expansion, minimizing blade tip clearance and improving efficiency during cruise.

• Uses fan/compressor air to cool turbine case
• Controls case thermal growth vs rotor
• Minimizes tip clearance in cruise
• Reduces tip leakage, improves fuel efficiency

Memory trick: ACC = a cooling blanket that shrinks the case to hug the blades

Internal partitions within integral fuel tanks that restrict fuel movement, reducing sloshing and surge loads during aircraft maneuvers.

• Found in integral/wet wing fuel tanks
• Reduce fuel surge and sloshing
• Help maintain stable CG during maneuvers
• Reduce structural stress from moving fuel mass

Memory trick: Baffles are speed bumps that keep fuel from sloshing wild

A starting ignition system that combines a vibrator (buzzer) with a retard breaker in the magneto to produce a rapid series of sparks at a retarded firing position during cranking, improving cold and normal starts.

• Vibrator rapidly interrupts battery current to feed the retard breaker points
• Retard breaker fires the magneto at a retarded position (safe for hand or starter cranking)
• Provides continuous sparking during cranking rather than a single impulse-coupling spark

Memory trick: A shower, not a drop — vibrator plus retard breaker makes sparks rain down at start.

The process of setting a magneto's breaker points to open exactly at the E-gap position (point of maximum flux change) using a timing light or buzzer box, performed before the magneto is installed and timed to the engine.

• Done off the engine using a timing fixture
• Precedes external timing to the crankshaft
• Ensures maximum voltage output at points opening

Memory trick: Internal timing = tuning the magneto's own clock before syncing it to the engine

The self-sustaining speed is the RPM at which a turbine engine can continue accelerating to idle without starter assistance, at which point the starter is disengaged.

• Occurs after light-off, before idle RPM is reached
• Starter cutout may be automatic or manual
• Premature cutout can cause a hung start
• Extended starter engagement risks starter overheating/damage

Memory trick: Self-sustaining = the engine 'leaves the nest' on its own power.

A repair process where a worn crankshaft journal is machined to a smaller standard undersize diameter, requiring matching undersize bearings to restore correct oil clearance.

• Undersize bearings are marked (e.g., 0.010 under) to match reground journals
• Only performed within manufacturer-approved undersize limits
• Oil clearance is verified with Plastigage or micrometer measurement after installation

Memory trick: Shrink the journal, shrink the bearing — they must always match in size!

Inspection of exhaust components for cracks, leaks, and corrosion, critical when the muffler is used as a heat source for cabin air.

• Cracks near cabin heat muffler shrouds risk carbon monoxide entering the cabin
• CO is colorless, odorless, and highly toxic
• Exhaust systems require inspection each annual/100-hour inspection per Appendix D

Memory trick: 'A cracked muffler can turn cabin heat into a silent killer'

A capacitor wired across the breaker points that absorbs the induced current surge at point opening, preventing arcing and enabling rapid primary field collapse for a strong spark.

• Located in parallel with breaker points
• Defective condenser causes arcing, burned points, weak spark
• Essential for rapid collapse of primary magnetic field

Memory trick: 'Condenser catches the spark surge before it burns the points'

A gear-driven supercharger is mechanically driven by the crankshaft, consuming engine power, while a turbocharger is driven by exhaust gas energy, recovering otherwise wasted energy.

• Gear-driven supercharger reduces net crankshaft power output
• Turbocharger uses exhaust-driven turbine to drive compressor
• Turbochargers generally more efficient due to using waste exhaust energy

Memory trick: Gear-driven steals crank power; turbo recycles exhaust power

Oils like 15W-50 have additives allowing them to maintain proper viscosity across a wide temperature range, flowing easily when cold and maintaining film strength when hot.

• W = winter/cold viscosity rating
• Second number = viscosity at operating temperature
• Multi-grade oils reduce cold-start wear
• Single-grade aviation oils are labeled simply, e.g., SAE 50

Memory trick: 15W-50: Winter-thin, Summer-thick, same bottle

A valve that opens at low compressor speeds to dump excess air from mid/rear compressor stages, preventing stall/surge caused by front-to-rear stage mismatch, then closes as speed increases.

• Open at low N2, closed at high N2
• Prevents compressor stall/surge
• Improves stage matching during acceleration
• Also called surge bleed or interstage bleed valve

Memory trick: Bleed valve = a pressure relief door that shuts as speed climbs

The ratio of compressor discharge total pressure to compressor inlet total pressure, indicating how much the compressor increases air pressure.

• Ratio = discharge pressure ÷ inlet pressure
• Multistage axial compressors can achieve ratios of 15:1 or higher
• Higher pressure ratios generally improve thermal efficiency

Memory trick: 'Discharge over Inlet, that's the ticket' - divide to get the ratio

The ratio of the mass airflow that bypasses the engine core (through the fan duct) to the mass airflow that passes through the engine core.

• High-bypass engines have ratios of 5:1 to over 10:1
• Higher bypass ratio improves fuel efficiency and reduces noise
• Low-bypass turbofans (military) may have ratios below 1:1

Memory trick: Bypass ratio: how much air skips the party (core) versus how much goes through it.

When timing a magneto to the engine, the drive gear must be indexed so the points open at the correct crankshaft angle AND the rotor aligns with the correct distributor segment for that cylinder.

• A magneto drive gear can often be installed in several tooth positions.
• Correct point-opening angle alone does not guarantee correct rotor alignment.
• Reindexing the gear one tooth at a time resolves both requirements together.

Memory trick: Right spark, wrong segment? Shift the gear one tooth to hit the target.

An ignition system using two independent magnetos and two spark plugs per cylinder to provide redundancy and improve combustion efficiency.

• Required by certification for most aircraft engines
• Improves flame propagation and reduces detonation risk
• Provides safety if one magneto fails in flight

Memory trick: Two sparks, twice as safe, twice as smooth burn.

A constant-speed propeller type where oil pressure drives blades to high pitch and counterweights, via centrifugal twisting moment, drive blades to low pitch.

• Loss of oil pressure = blades move to low pitch = possible overspeed
• Opposite of some non-counterweight designs where oil pressure decreases pitch
• Counterweights use centrifugal force acting on offset weights attached to blade shanks

Memory trick: No oil, no push to HIGH pitch — counterweights fling blades LOW, RPM runs away

An ice protection system using electrical resistance heating elements bonded to propeller blade leading edges, cycled on/off by a timer via slip rings.

• Uses resistance heating elements on blades
• Power delivered through slip rings and brushes
• Timer cycles heat to conserve electrical power

Memory trick: Electro-heat melts the frost, cycle by cycle

A heat exchanger (fuel-oil or bleed air) that warms turbine engine fuel to prevent ice crystal formation from clogging fuel filters at low temperatures.

• Also serves as an oil cooler by transferring heat from oil to fuel
• Prevents fuel filter icing at high altitude/low temperature
• Often has a bypass valve if the filter becomes blocked

Memory trick: Fuel heater = a tiny sunbath that melts ice before it clogs the filter

A crankshaft-mounted mass that swings on oversized pin holes to absorb torsional vibrations occurring at specific engine operating frequencies.

• Tuned to a particular vibration frequency, not all frequencies
• Prevents crankshaft fatigue cracking from torsional resonance
• Common on large radial and horizontally opposed engines

Memory trick: Swinging weights soak up the shaky twist

The precise gap between pump gears and housing in a positive-displacement gear-type oil pump; excessive clearance allows internal oil slippage, reducing pump output and system oil pressure.

• Wet-sump engines commonly use gear-type positive-displacement oil pumps
• Clearance must be checked against manufacturer limits during overhaul
• Excessive clearance is most noticeable as low oil pressure at idle/low RPM

Memory trick: Loose gears leak oil backward like a leaky faucet.

A spring-loaded valve inside the fuel pump that routes excess fuel back to the pump inlet to hold outlet pressure constant despite changes in RPM.

• Maintains steady fuel pressure to carburetor
• Failure causes pressure to rise with RPM
• Excess pressure causes overly rich mixture

Memory trick: Relief valve is the pressure 'safety valve' bleeding off extra fuel like a pot's steam vent.

A precision measurement of through-bolt length or diameter change used to detect permanent elongation from overtorque or fatigue during crankcase overhaul.

• Through-bolts clamp crankcase halves together under high tension
• Stretch beyond manufacturer limits indicates permanent deformation
• Bolts exceeding the stretch limit must be replaced, never reused

Memory trick: A stretched bolt is like an overused rubber band — once it's past its limit, it's junk.

A supercharger is mechanically driven off the crankshaft and consumes engine power to boost induction pressure; a turbocharger uses exhaust gas energy through a turbine to drive the compressor without direct crankshaft power.

• Supercharger: gear/clutch-driven from crankshaft
• Turbocharger: exhaust-driven turbine wheel
• Turbocharger uses wastegate to regulate boost pressure

Memory trick: Supercharger borrows power from the crank; turbocharger recycles wasted exhaust.

Regulation listing the minimum required items for annual and 100-hour inspections, divided into airframe, engine, and other groups.

• Engine group includes mounts, cylinders, hoses, exhaust, oil system, and controls
• 100-hour inspections use the same scope as annual inspections
• Appendix D is the baseline checklist mechanics must follow

Memory trick: 'Mounts Move the Motor' — check engine mounts first in the powerplant group

A capacitor discharge ignition exciter stores high-voltage energy that can remain dangerous even after the aircraft electrical system is shut down, requiring a waiting/discharge period before maintenance.

• Stored charge can be lethal even with power removed from the aircraft
• Manufacturer specifies a minimum wait time before handling the unit
• Never handle exciter leads or terminals until verified discharged

Memory trick: CD exciter holds its charge like a loaded spring — wait before you touch it.

A spring-loaded mechanism on one magneto that retards spark timing during cranking and then snaps the magneto rotor rapidly for a strong, retarded spark to aid starting.

• Used only on one magneto (usually the left/impulse mag)
• Produces a retarded, hot spark for easy starting
• Releases automatically once engine reaches a set RPM

Memory trick: Impulse = 'I Snap for Start' — winds up, snaps, sparks hot

A turbofan thrust reverser that blocks bypass duct airflow with doors and redirects it forward through fixed cascade vanes to produce reverse thrust.

• Common on high-bypass turbofan engines
• Blocker doors close off normal duct flow path
• Distinct from clamshell/target reversers used on turbojets

Memory trick: 'Cascade' sounds like a waterfall — air cascades forward through the vanes.

A manufacturing feature where the cylinder bore near the head is slightly smaller than at the skirt, compensating for greater thermal expansion at the hotter head end so the bore is uniform at operating temperature.

• Also called a 'choked' cylinder
• Compensates for uneven heat distribution along the barrel
• Bore becomes round/uniform once at operating temperature

Memory trick: Choke it cold, round it hot — the top starts tight to end up true.

A magneto that continues to fire with the ignition switch OFF because its primary grounding (P-lead) circuit is broken.

• Switch OFF normally grounds the primary circuit through the P-lead, stopping magneto firing.
• A broken P-lead leaves the magneto ungrounded and capable of firing at any time.
• Always treat a propeller as if the ignition is live, regardless of switch position.

Memory trick: No ground, no OFF — a broken wire keeps the mag alive.

A float carburetor uses the pressure drop created by airflow through a venturi to draw fuel from the discharge nozzle in proportion to engine airflow demand.

• Higher airflow = lower venturi pressure = more fuel drawn
• Based on Bernoulli's principle
• Float chamber remains near atmospheric pressure
• Fuel discharge nozzle is located at the venturi throat

Memory trick: Faster air, lower pressure, more fuel sucked up — Bernoulli's bar trick

The primary lead (P-lead) grounds the magneto when the ignition switch is OFF; if disconnected or broken without an alternate ground, the magneto remains "hot" and can fire if the propeller is turned.

• Switch OFF grounds the magneto through the P-lead
• An open P-lead = magneto stays live/hot
• Always treat propeller as if the ignition is on when P-lead is disconnected

Memory trick: No ground on the P-lead means the prop can bite—treat it as LIVE.

A test using a megohmmeter to measure the insulation resistance of high-tension ignition leads, verifying they can safely contain high voltage without leakage or arcing.

• Performed with a megohmmeter per manufacturer specifications
• Low resistance indicates deteriorated, cracked, or contaminated insulation
• Risk of voltage leakage increases at altitude due to lower air pressure
• Failed leads are replaced to prevent engine misfire or rough running at altitude

Memory trick: Low resistance, high risk — voltage escapes through cracked insulation.

In a radial engine, the master rod connects directly to the crankshaft crankpin; the remaining link (articulating) rods attach to knuckle pins on the master rod's big end.

• One master rod per row of cylinders
• Link rods pivot on knuckle pins around master rod
• Design allows multiple cylinders to share one crankpin

Memory trick: Master rod is the hub of a wheel—other rods (spokes) attach to it, not the axle directly.

A temperature-sensitive valve that routes oil around the cooler when cold to speed warm-up and through the cooler when hot to control operating temperature.

• Opens bypass when oil is cold, sending oil directly to engine
• Closes bypass and routes oil through cooler core when oil is hot
• Protects against excessive pressure drop through a cold cooler core

Memory trick: Cold oil takes the shortcut; hot oil takes the scenic cooler route.

Synthetic ester-based lubricants are used in turbine engines for their superior high-temperature stability and low-temperature flow characteristics compared to mineral oils.

• Turbine oils must resist oxidation at very high bearing temperatures
• Must flow adequately for cold starts at altitude
• Synthetic esters resist thermal breakdown better than petroleum oils

Memory trick: Synthetic oil survives both fire and ice (hot and cold extremes)

A non-contact (or light-contact) seal using rotating knife-edges against an abradable stationary lining to minimize air or oil leakage in a turbine engine.

• Reduces, but does not fully eliminate, leakage across rotating/stationary interfaces
• Abradable lining allows brief rubbing without seal damage
• Common at compressor/turbine disc interfaces and bearing compartments

Memory trick: Labyrinth seal = a maze that slows leaks but never fully blocks them