FAA Aviation Mechanic - Powerplant (AMP) flashcards

32 cards. Read the term and the definition here. The deck at the top of this page is optional.

Compression ratio

The ratio of total cylinder volume with the piston at bottom dead center to clearance volume with the piston at top dead center; it influences power output and the required fuel octane rating.

Firing order

The sequence in which cylinders deliver power strokes, chosen to balance crankshaft loads; a four-cylinder Lycoming opposed engine typically fires 1-3-2-4.

Cylinder barrel choke

A deliberate slight taper in an air-cooled cylinder barrel that makes the bore smaller at the top so piston-to-wall clearance remains correct as the hotter top end expands.

Valve clearance

The gap between the rocker arm and valve stem tip, measured with the cylinder at top dead center on the compression stroke, ensuring the valve seats fully when hot.

Brayton cycle

The constant-pressure thermodynamic cycle of a gas turbine: compression, combustion at constant pressure, expansion through the turbine, and exhaust, replacing the reciprocating engine's four strokes.

N1 and N2

Spool speeds in a twin-spool turbine engine: N1 is the low-pressure or gas-producer compressor speed and N2 is the high-pressure compressor speed, both read as percent RPM.

Compressor stall

A disruption of airflow through the compressor that causes low power, rising exhaust temperature, and rumbling; it can be cleared by reducing power or opening bleed valves.

Turbine blade creep

Permanent elongation of turbine blades caused by high temperature combined with centrifugal load; it is checked by measuring blade length against new-part limits.

Differential compression test

A leakdown check in which regulated air at a set pressure, typically 80 psi, is applied to a cylinder through the spark plug hole and the pressure held indicates ring and valve sealing.

Boroscopic inspection

Examination of cylinder interiors, combustion chambers, and turbine hot sections with a small optical instrument inserted through a port, allowing internal inspection without engine disassembly.

Magnetic particle inspection

A method that magnetizes a ferromagnetic part and applies iron particles; flux leakage at a surface or near-surface defect attracts the particles and reveals the flaw.

Thermocouple probe

A temperature sensor of two dissimilar metals joined at a hot junction that produces a small voltage proportional to temperature, used for exhaust gas and cylinder head indications.

Manifold pressure gauge

An absolute-pressure instrument calibrated in inches of mercury that shows intake manifold pressure on a reciprocating engine and indicates power output; readings above 30 in Hg indicate boost.

Instrument range markings

Colored arcs and radial lines on or adjacent to an instrument dial that define normal, caution, maximum, and special operating ranges, such as green, yellow, red, and white.

Continuous-loop fire detector

A detector with a temperature-sensitive element routed through the engine compartment that changes resistance when heated and triggers a warning; a short or open also causes an alarm.

Firewall shutoff valve

A valve at the firewall that stops the flow of fuel, hydraulic fluid, or bleed air into the engine compartment when actuated by the fire handle or fire switch.

Halon 1301

A clean, electrically nonconductive extinguishing agent that interrupts the combustion chain reaction and leaves no residue, but has been phased out for environmental reasons.

Starter-generator

A single machine that cranks the engine as a series-wound motor and then generates electrical power after starting; a cutout relay prevents battery discharge through it.

Voltage regulator

A device that controls generator or alternator field current to hold system voltage within limits and prevent overcharging; an overvoltage relay opens the field circuit if voltage is excessive.

Dry-sump oil system

A lubrication system in which oil is scavenged from the engine to an external tank and then returned under pressure, allowing a smaller sump and better oil cooling.

Oil pressure relief valve

A spring-loaded valve that bypasses oil when pressure exceeds a set value, limiting maximum system pressure and protecting the oil cooler, lines, and engine.

Ashless dispersant oil

A mineral oil with additives that hold contaminants in suspension and prevent sludge; used in normally aspirated opposed engines after break-in, while straight mineral oil is used during break-in.

Impulse coupling

A spring-loaded magneto device that retards spark timing and delivers a hot, late spark for starting, then disengages automatically once engine speed rises above a set value.

Turbine igniter plug

A high-energy spark plug used in turbine engines, powered by an exciter that stores and discharges energy; it operates during starting and relight rather than continuously.

Magneto P-lead

The wire connecting a magneto to the ignition switch; the switch grounds the primary circuit through this lead to stop the engine, so a broken lead leaves the magneto hot.

Float carburetor

A carburetor using a float-operated needle valve to hold a constant fuel level in a chamber, from which fuel is drawn through a metering jet into the venturi airflow.

Carburetor icing

Ice that forms in the venturi and throttle area when fuel vaporization and pressure drop cool moist air below freezing; most likely at 20 to 70 degrees Fahrenheit with high humidity.

Fuel control unit

The turbine fuel system component that meters fuel to the combustor based on throttle position, compressor speed, and other parameters; it may be hydromechanical or part of a FADEC.

Critical altitude

The highest altitude at which a turbocharged engine can produce its rated manifold pressure with the wastegate fully closed; above it, available power decreases with altitude.

Wastegate

A valve in the exhaust path that bypasses exhaust gas around the turbocharger turbine to control boost; closing it increases turbine speed and manifold pressure.

Constant-speed propeller

A propeller whose blade angle is automatically adjusted by a governor to maintain a selected engine RPM as airspeed, altitude, and power settings change.

Feathering propeller

A propeller whose blades rotate to approximately the zero-thrust position edge-on to the airflow, reducing drag from a failed engine on a multi-engine aircraft.