FAA Aviation Mechanic Powerplant (AMP) flashcards

Deposits on spark plug electrodes that indicate specific engine operating problems.

• Carbon fouling: dry black soot from rich mixture or idling
• Lead fouling: gray/tan deposits from leaded fuel additives
• Oil fouling: wet oily coating from excessive oil consumption

Memory trick: 'Black and fluffy means too much fuel is stuffy'

A carburetor component that injects a momentary extra charge of fuel when the throttle is opened rapidly, preventing lean hesitation.

• Prevents lean-out during rapid throttle advancement
• Operated mechanically by throttle linkage
• Malfunction causes hesitation or stumble on acceleration

Memory trick: Accelerator pump = a quick fuel squirt to keep pace with air rush

A turbine engine starting device that uses compressed air to spin a small turbine, geared down to drive the engine's high-pressure spool through an automatic disengaging clutch.

• Air source can be APU, ground cart, or engine cross-bleed
• Reduction gearing lowers turbine speed to usable starter output speed
• Clutch automatically disengages at self-sustaining engine speed

Memory trick: Pneumatic starter = a tiny turbine spun by a gust of borrowed air

A fuel quantity sensing device where a float-actuated wiper arm varies resistance on a rheostat, changing current in the indicator circuit to display fuel quantity in the cockpit.

• Float position varies sender resistance
• Resistance change alters circuit current
• Cockpit gauge interprets current as fuel quantity
• Common in light, piston-powered aircraft

Memory trick: Float rises, resistance changes, current tells the tale of fuel level

A component in some hydromatic feathering systems that stores high-pressure oil to enable rapid propeller feathering.

• Stores oil under pressure for feathering
• Provides immediate high-pressure oil surge
• Works with feathering pump for a failed-engine's low oil pressure

Memory trick: Accumulator is the 'emergency oil tank' for fast feathering

Flange runout is measured with a dial indicator while rotating the crankshaft to ensure the propeller mounting surface is true; exceeding the manufacturer's TIR limit requires rejection of the crankshaft.

• Measured using a dial indicator and total indicator reading (TIR)
• Excessive runout causes propeller vibration and crankshaft fatigue
• Limits are specified in the manufacturer's overhaul/service manual
• Runout cannot be corrected by torque adjustment; crankshaft must be repaired/replaced

Memory trick: 'Over the Limit, Out It Goes' — exceeding TIR means the crankshaft is rejected.

Uncontrolled, explosive combustion of the fuel-air charge ahead of the normal flame front, caused by using fuel with insufficient antiknock rating for the engine's compression ratio, leading to severe pressure spikes and potential engine damage.

• Low octane fuel increases susceptibility to autoignition
• Produces audible knocking and rapid cylinder pressure rise
• Can cause piston, ring, and valve damage if uncorrected

Memory trick: Low octane = short fuse for an engine explosion.

The waiting period after engine shutdown required for oil in lines and components to return to the sump before an accurate dipstick reading can be taken.

• Checking oil too soon after shutdown gives falsely low readings
• AFM/POH specifies required wait time (commonly several minutes)
• Applies to wet-sump systems where sump quantity is the total system indicator

Memory trick: Give the oil time to come home before you count it.

A spring-loaded valve in a full-flow oil filter that opens when the filter element becomes clogged, allowing unfiltered oil to continue lubricating the engine.

• Opens based on differential pressure across the filter element
• Prevents oil starvation from a clogged filter
• Better to circulate unfiltered oil than none at all

Memory trick: When the filter clogs, the bypass door swings open — flow must go on!

Net thrust equals mass flow rate (in slugs/sec) multiplied by the change in velocity between exhaust and inlet: F = (W/g)(Ve − Vo).

• W = mass airflow in lb/sec
• g = 32.2 ft/sec²
• Ve = exit velocity, Vo = inlet velocity
• Pressure thrust term often added for full gross thrust

Memory trick: Thrust = mass × speed gain, divided by gravity's pull

The distance between center and ground electrodes, measured with a round wire gauge matched to the electrode shape for accuracy.

• Round wire gauges match curved electrodes
• Flat feeler blades give false readings on round electrodes
• Gap must meet manufacturer spec (commonly 0.012–0.019 in.)
• Improper gap affects spark energy and plug life

Memory trick: Round plug, round tool — match the shape to get the truth.

Applying carburetor heat introduces warm, less dense air into the induction system, reducing power and enriching the fuel/air mixture, useful for melting ice but causing a slight performance penalty when no ice is present.

• Warm air is less dense, reducing volumetric efficiency and power
• Mixture becomes richer since fuel metering is based on airflow volume
• Should be used cautiously since it can promote detonation if misused during high power settings

Memory trick: Hot air thins power and thickens the mix

A piston pin free to rotate in both the piston bosses and the connecting rod bushing, retained axially by plugs or retaining rings.

• Rotates freely in both piston and rod
• Retained by plugs, snap rings, or spring clips
• Distributes wear evenly around the pin circumference

Memory trick: Full-floating pin floats free in BOTH holes, held by end plugs.

A single magneto housing containing two independent sets of breaker points, coils, and distributor components, providing the redundancy of two magnetos with reduced weight and a single drive.

• Still fires two spark plugs per cylinder for redundancy
• Failure of one internal circuit does not disable the other
• Used on some high-performance/aerobatic and certain light aircraft engines

Memory trick: Dual magneto = 'two hearts, one body' — redundancy without extra weight

A condition where fuel vaporizes within fuel lines due to high temperature and low pressure, disrupting fuel flow, commonly occurring during hot restarts after heat soak.

• Caused by heat soak plus low pressure on suction side of pump
• More common in hot weather and after shutdown of hot engine
• Can cause rough running, power loss, or engine stoppage
• Boost pumps can help by increasing pressure to suppress vapor formation

Memory trick: Hot soak plus low pressure lets fuel boil into bubbles that choke the line

A vent line that relieves crankcase pressure caused by piston ring blow-by gases, routing them overboard; blockage causes pressure buildup and potential oil leaks.

• Vents combustion blow-by gases from crankcase
• Blockage (often by ice) raises internal crankcase pressure
• Excess pressure can force oil out at seals, gaskets, or dipstick

Memory trick: 'Blocked breather, oil goes everywhere'

The propeller control range below flight idle where blade angle is controlled directly by power lever position rather than by the constant-speed governor, used for ground operations and reverse thrust.

• Below flight idle gate on the power/condition lever quadrant
• Allows low pitch, zero pitch (disc), or reverse pitch selection
• Used for taxi, landing rollout, and reverse thrust operations

Memory trick: Beta range = 'Below' flight idle, blades obey the lever directly

Manufacturer-specified allowable limits for dressing out minor nicks, scratches, and pitting on metal propeller blades without replacement.

• Stress risers from nicks can lead to fatigue cracking if not corrected
• Blending must maintain smooth contour and stay within depth/width limits
• Leading edge damage is a common area of inspection due to erosion and impact

Memory trick: 'Small nicks get smoothed, not scrapped'

Carburetor ice can form in a wide temperature range (roughly 20°F–70°F, extending to near 100°F) whenever relative humidity is high, due to rapid cooling from fuel vaporization and venturi pressure drop.

• Most likely with visible moisture or high humidity
• Can occur even on a warm, humid day
• Descent/low power settings increase risk (reduced airflow, cooler venturi)

Memory trick: 'Humid air hides ice, even when it's warm'

Ball bearings support combined radial and thrust loads at a fixed shaft location, while roller bearings support radial loads and allow axial shaft expansion.

• Ball bearings act as a thrust-locating bearing
• Roller bearings allow shaft to grow with heat without binding
• Bearing sumps with carbon seals retain lubricating oil

Memory trick: 'Ball = Both loads, Roller = Room to grow.'

A serrated, wedge-shaped blade root that slides into a matching disc slot, securing the blade against centrifugal loads while allowing removal for maintenance.

• Used on compressor and turbine blades
• Transfers centrifugal load to disc
• Allows individual blade replacement
• Common shapes: fir-tree, dovetail

Memory trick: Fir-tree root = a pine tree locked into the disc

Track verifies all blade tips travel in the same plane; balance verifies even weight distribution to prevent vibration.

• Track checked with a fixed pointer/board and rotating prop by hand
• Balance can be static (bench) or dynamic (running engine)
• Out-of-track or out-of-balance both cause vibration but from different causes

Memory trick: Track = path of the tips, Balance = weight of the blades

A time-dependent plastic deformation of turbine disc material caused by prolonged exposure to high centrifugal stress and elevated temperature, which can lead to disc growth or eventual failure.

• Accelerated by overspeed and overtemperature events
• Tracked via life-limited parts programs (cycle counting)
• Can eventually cause disc burst if undetected

Memory trick: Creep: the disc slowly 'stretches like taffy' under heat and spin.

A maintenance procedure that verifies and adjusts a turbine engine's fuel control unit so the engine achieves its rated thrust output at a specified reference power setting under known ambient conditions.

• Performed after FCU installation, adjustment, or engine change
• Uses EPR, EGT, or N1 relationships compared to reference charts corrected for OAT/pressure
• Ensures engine meets thrust output without exceeding temperature/speed limits

Memory trick: Engine trim = fine-tuning the throttle's promise to deliver exact rated thrust

The period during which both intake and exhaust valves are open simultaneously near top dead center, aiding scavenging and cooling.

• Occurs near end of exhaust stroke/beginning of intake stroke
• Helps cool exhaust valve using incoming fresh charge
• Improves cylinder scavenging of burned gases

Memory trick: Overlap opens both doors briefly to sweep out the heat

A diverging fairing located aft of the last turbine stage that streamlines gas flow around the rear bearing support and diffuses velocity into pressure before the exhaust nozzle.

• Covers/fairs the rear bearing support strut
• Provides increasing flow area (diffuser) behind turbine
• Aids pressure recovery prior to nozzle expansion

Memory trick: The tailcone is a smooth umbrella diffusing flow around the bearing strut.

The portion of a turbine lubrication system that returns oil from bearing sumps to the tank; sized larger than the pressure pump because scavenged oil is aerated and expanded by heat.

• Scavenge pump capacity exceeds pressure pump capacity
• Aeration and heat expand oil volume in sumps
• Prevents sump oil flooding and overheating

Memory trick: Scavenge pumps are 'oversized vacuum cleaners' because hot, frothy oil takes up more space.

A trend-monitoring program that analyzes trace metal content in used engine oil samples to detect abnormal component wear before failure occurs.

• Iron/chromium indicate steel or chrome-plated part wear
• Copper/silver often indicate bearing or bushing wear
• Trends over multiple samples are more meaningful than a single reading

Memory trick: Metal in the oil is a message — iron spikes whisper 'something's wearing away!'

A radial (tower) driveshaft geared to the engine's main rotor shaft transmits power to the accessory gearbox, which drives fuel pumps, oil pumps, and generators.

• Tower shaft connects main shaft to accessory gearbox
• Gearbox mounts fuel pump, oil pump, generator, hydraulic pump
• Located typically at the bottom of the engine for accessibility

Memory trick: Tower shaft = the 'power line' running down from the main shaft to the accessory 'power strip.'

Multiple thermocouple probes around the turbine exhaust are wired in parallel to produce a single averaged temperature reading for the cockpit indicator.

• Uses chromel-alumel thermocouples typically
• Parallel wiring averages millivolt signals
• Prevents a single hot spot from giving a misleading reading

Memory trick: Many probes, one number — parallel wiring blends readings into an average.

Avgas is graded by an antiknock/performance number that indicates its resistance to detonation under lean and rich mixture conditions.

• 100LL = 100 octane rating, low lead
• Higher numbers indicate greater detonation resistance
• Grade is dyed blue for 100LL identification

Memory trick: '100' fights knock, 'LL' keeps lead low.

A mechanical stop that prevents constant-speed propeller blades from moving below the minimum design blade angle, protecting against ground/engine overspeed.

• Works with the governor to limit blade travel range
• Failure allows blades to flatten too much, causing overspeed
• Distinct from the governor's speeder spring, which sets governed RPM

Memory trick: If the stop fails, the blade goes flat and the engine screams past its limit.

Air tapped from turbine engine compressor stages used for cabin pressurization, anti-icing, and pneumatic engine starting, rather than for producing thrust.

• Tapped from various compressor stages depending on pressure needed
• Reduces available thrust slightly when in use
• Common bleed uses: pressurization, anti-ice, pneumatic start

Memory trick: 'Bleed Air Serves, not Thrust' — it helps systems, not propulsion.

A digital electronic system with complete authority over turbine engine operation, including fuel scheduling, starting, and limit protection.

• Full Authority = no separate hydromechanical backup needed
• Uses engine sensors and an Electronic Engine Control (EEC) computer
• Automatically protects against exceedances like overspeed and overtemperature

Memory trick: FADEC: Fully Automatic, Digital, Engine Command

On engines with solid lifters, valve clearance is measured with a feeler gauge only when the piston is at TDC compression, ensuring both valves are closed and the cam follower is on the base circle.

• Applies to radial and some opposed engines with solid lifters
• TDC compression = both valves closed
• Feeler gauge measures rocker-to-valve stem gap
• Out-of-limit clearance affects valve timing and engine performance

Memory trick: 'Compression Closes the Case' — TDC compression closes both valves for a true reading.

A force created by air pressure acting ahead of the blade's pitch-change axis that tends to twist the blade toward a higher (coarser) pitch angle, opposing the centrifugal twisting moment.

• Center of pressure is ahead of pitch axis
• Tends to increase (coarsen) blade angle
• Opposes centrifugal twisting moment
• Both moments factor into governor/counterweight design

Memory trick: Air pushes forward, blade turns coarse — 'Aerodynamic Aims high.'

The primary (P) lead grounds the magneto when the ignition switch is OFF; if it is broken or disconnected, the magneto remains 'hot' even with the switch off.

• P-lead ground failure is a common cause of prop strikes
• Always treat propellers as if the ignition is live
• Ground checks are part of 100-hr/annual inspections

Memory trick: 'P' for Protect — a broken P-lead means the mag is still alive

A turbine engine heat exchanger that uses fuel to cool hot lubricating oil while simultaneously warming the fuel to prevent fuel filter icing.

• Fuel and oil never physically mix
• Cools oil, warms fuel simultaneously
• Reduces need for a separate air-cooled oil cooler

Memory trick: Fuel-oil cooler is a 'heat swap meet': hot oil trades warmth for cold fuel.

A restricted RPM range placarded to prevent sustained operation at a frequency that causes harmful resonant vibration in the propeller/engine system.

• Caused by resonance matching natural frequency
• Continuous operation prohibited, momentary transit allowed
• Can lead to fatigue cracking if ignored

Memory trick: Red-line range rings like a struck bell too long

A piston skirt machined slightly oval, smaller in diameter along the pin axis than perpendicular to it, so it becomes round when heated due to greater expansion at the pin bosses.

• Pin boss area has more mass and expands more when hot
• Cold piston is intentionally out-of-round
• Piston becomes round at normal operating temperature for proper fit

Memory trick: 'Egg-shaped when cold, round when hot'

A power turbine stage mechanically independent of the gas generator, driven purely by exhaust gas energy and connected to the propeller through a reduction gearbox.

• Also called the power turbine
• Mechanically separate shaft from gas generator
• Allows propeller speed to be controlled independently of N1

Memory trick: 'Free' means it floats on gas flow, not bolted to the gas generator.

A valve that controls the amount of exhaust gas routed through the turbine, regulating turbocharger speed and manifold pressure (boost).

• Located in exhaust system ahead of/around turbine
• Diverts exhaust overboard to limit boost
• Can be manually or automatically controlled

Memory trick: Wastegate = the exhaust's escape door that limits how hard the turbine spins.

The generally accepted minimum acceptable cylinder pressure using an 80 psi calibrated orifice tester is 60/80 psi (about 25% leakage).

• Test performed with piston at TDC on compression stroke
• 60/80 psi (25% loss) is the common investigation threshold
• Leakage source identified by listening at exhaust, intake, or crankcase breather

Memory trick: '60 out of 80 — time to worry, ya know'

Oil consumption is tracked as a rate (quarts per flight hour) and compared against the manufacturer's published limit to detect developing engine wear.

• Rate = hours flown ÷ quarts added
• Rising consumption trend can indicate ring, valve guide, or seal wear
• Compared against manufacturer TCDS or service manual limits
• Used alongside compression tests and oil analysis for engine health monitoring

Memory trick: 'Divide Hours by Quarts to Judge the Squirts' — calculate the rate before judging.

An operating range in which the power lever directly controls propeller blade angle, from flight idle through reverse pitch, rather than the governor alone.

• Used mainly for ground operations: taxi, landing rollout, reverse thrust
• Bypasses normal governor-only constant-speed control
• Distinct from Alpha range, where governor controls pitch for flight

Memory trick: Beta = Braking on the ground, direct lever control down to reverse

A measure of turbine engine fuel efficiency calculated as fuel flow divided by net thrust produced.

• Units are lb fuel/hr per lb of thrust
• Lower TSFC = more efficient engine
• Used to compare engines of different thrust classes

Memory trick: TSFC: how much fuel it costs to buy one pound of push.

A high-energy capacitor-discharge (CD) system that provides an intense spark for engine starting and occasional relight, unlike continuously firing reciprocating engine magnetos.

• Used only during start and relight, not continuously
• Exciter unit stores and discharges high-voltage energy
• Delivers spark via igniter plugs, not spark plugs

Memory trick: 'CD system: Charge, Discharge, Done' — one big spark to start, then quiet.

The E-gap is the small angular displacement past the rotating magnet's neutral position at which breaker points should open, producing the maximum rate of flux change and strongest spark.

• E-gap stands for 'efficiency gap'
• Occurs a few degrees after the magnet's neutral position
• Breaker points must open exactly at E-gap for correct internal timing
• Improper E-gap timing reduces spark energy and can cause hard starting/misfires

Memory trick: 'Past Neutral, Peak Power' — E-gap is just after neutral where voltage peaks.

The small gap in the valve train that allows for thermal expansion; too little clearance prevents full valve seating and causes burning, while too much clearance causes noise and reduced lift.

• Too tight = valve doesn't fully close, burns valve
• Too loose = noisy, reduced valve lift/timing accuracy
• Checked and adjusted with feeler gauge per manufacturer spec

Memory trick: Too tight, valve can't shut tight—hot gas burns it out.

A capacitor wired across the breaker points that absorbs induced voltage to prevent arcing and ensures rapid primary current collapse for a strong secondary spark.

• Wired in parallel with breaker points
• Prevents point burning/arcing
• Enables rapid magnetic field collapse
• Weak condenser causes weak spark and pitted points

Memory trick: Condenser catches the spark that would burn the points

Cold, viscous oil increases engine cranking drag, slowing magneto rotor speed and reducing spark energy, making preheating important for reliable ignition during cold-weather starts.

• Magneto output is speed-dependent, weakest at low RPM
• Cold oil increases mechanical drag on cranking
• Preheating reduces drag, restoring adequate cranking speed
• Preheating also aids fuel vaporization and reduces engine wear

Memory trick: Cold oil = molasses drag = slow crank = weak spark.

Fins machined or cast onto cylinder heads and barrels that increase surface area for air cooling; combined with baffles, they direct airflow to prevent localized overheating.

• Increase heat transfer surface area
• Work with baffles to direct cooling airflow
• Damage can cause hot spots leading to detonation or cracking

Memory trick: Broken fins = a broken radiator grille, letting hot spots form.

A cruise leaning technique where the mixture is set slightly rich of peak EGT (approximately 50-100°F rich) to achieve maximum power output while maintaining a safety margin from peak cylinder temperatures.

• Best power: ~50-100°F rich of peak EGT
• Best economy: leaned to peak EGT or slightly lean of peak
• Full rich used for takeoff/climb, not cruise leaning

Memory trick: Rich of peak for punch, lean of peak for pennies.

Full-flow filtration routes all engine oil through the filter before it reaches bearings; partial-flow (bypass) filtration only filters a portion of oil flow, sending the rest directly to the engine.

• Full-flow provides more complete filtration
• Full-flow systems include a bypass valve for clogged filters
• Most modern reciprocating engines use full-flow filtration

Memory trick: Full-flow = 'everyone through the checkpoint'; partial-flow = 'only a few get checked.'

A component in continuous-flow fuel injection systems that receives metered fuel and distributes it evenly and proportionally to each cylinder's fuel injector nozzle.

• Located downstream of the fuel control unit
• Contains a spring-loaded diaphragm/valve that opens with increasing fuel flow
• Ensures balanced fuel distribution among cylinders

Memory trick: The divider is the 'fuel referee' splitting flow fairly.

A mechanical pop-out (or electrical) indicator signals when the pressure drop across a fuel filter exceeds a set limit, indicating the filter element is becoming clogged.

• Differential pressure = inlet pressure minus outlet pressure
• A popped indicator means the filter is restricting fuel flow
• A bypass valve opens if the filter becomes fully blocked to ensure continued fuel flow

Memory trick: Subtract the pressures — if it's more than 5, the filter's clogged, don't drive!

A system that controls both propeller RPM matching and the phase angle between propellers on multi-engine aircraft to reduce cabin noise and vibration.

• Goes beyond basic synchronizing (RPM-only matching)
• Reduces beat frequency noise from mismatched blade phase
• Common on turboprop and some piston twin aircraft

Memory trick: Synchronize = same SPEED; Synchrophase = same speed AND same BEAT

Increasing the number of propeller blades increases total blade area (solidity), allowing the propeller to absorb the same engine power with a smaller diameter.

• More blades = more solidity
• Smaller diameter possible for same power absorption
• Useful when ground clearance is limited
• Common on high-horsepower turboprops and radials

Memory trick: More blades, less room needed — pack the power into a smaller circle.

A numerical rating of a fuel's resistance to detonation; higher numbers allow higher compression/manifold pressure without knock.

• 100LL = 100 octane, low lead
• Higher octane = greater detonation resistance
• Using lower-than-specified octane fuel can cause detonation

Memory trick: 'Octane Outlasts Overheating' — higher octane resists knock longer

The gap between the distributor rotor finger and block electrode requires higher voltage to jump as it wears larger, increasing flashover risk at altitude where air is less dense.

• Part of high-tension secondary ignition circuit
• Excess wear increases required firing voltage
• Thin air at altitude reduces dielectric strength
• Can cause internal flashover instead of spark plug firing

Memory trick: Thin air + big gap = spark takes the shortcut inside.