FAA Aviation Mechanic Powerplant (AMP)

B. Inertia of the pinion causes it to screw forward along helical splines on the rapidly rotating armature shaft

In a Bendix (inertia) drive, the pinion is mounted on a helically splined sleeve. When the starter motor spins up quickly, the pinion's inertia causes it to lag momentarily and screw forward along the splines into mesh with the ring gear. Once the engine starts and overspeeds the pinion, it automatically screws back out of mesh.

C. To admit compressor discharge air that forms a cooling air film along the liner wall

Combustor liners use film/effusion cooling holes that admit compressor discharge air, which flows along the inner wall as a protective film, insulating the liner from the extreme radiant and convective heat of combustion gases.

D. Oil returning from the bearings is aerated (mixed with air), increasing its volume and requiring greater capacity to return it to the tank

As oil passes through bearing compartments, it becomes aerated with air, significantly increasing its volume. The scavenge pump must therefore have greater capacity than the pressure pump to ensure all the aerated oil is returned to the tank and bearing sumps do not flood, even though the mass of oil is the same.

D. Only with the engine stopped, by loosening the clamping mechanism at the hub and manually resetting each blade

A ground-adjustable propeller has a fixed pitch during flight; the blade angle can only be reset on the ground with the engine stopped by loosening the hub clamping mechanism, rotating the blades to the desired angle, and re-tightening. There is no in-flight or governor-controlled pitch change capability on this type of propeller.

A. To contain fragments of a fan blade if one fails, preventing them from penetrating the fuselage or wing

The fan containment case is a certification requirement (per 14 CFR Part 33) designed to contain a released fan blade and its fragments within the engine nacelle, preventing damage to the aircraft structure, fuel tanks, or control systems in the event of a blade failure.

D. Compressor inlet air temperature and pressure, engine speed, and throttle (power lever) position

A hydromechanical FCU meters fuel based on compressor inlet pressure (Pt2) and temperature (Tt2), engine rotor speed, and throttle lever position, allowing it to schedule the correct fuel flow for acceleration, deceleration, and steady-state operation while protecting against compressor stalls and overtemperature.

D. Oil is being drawn past the worn intake valve guide into the combustion chamber during the intake stroke

A worn or excessively clearanced valve guide can allow oil from the valve spring/rocker area to be drawn down the valve stem into the combustion chamber, particularly during the intake stroke when manifold vacuum pulls oil past the loose guide. This produces bluish-gray exhaust smoke and increased oil consumption without necessarily affecting differential compression readings, since compression seal is governed by valve seating and piston rings, not guide clearance.

B. To continuously spray a metered fuel flow into the intake airstream near the intake valve for vaporization before entering the cylinder

Continuous-flow fuel injection nozzles spray fuel continuously (not timed to valve events) into the intake port just upstream of the intake valve, where it mixes with incoming air and vaporizes before entering the cylinder. Fuel division among cylinders is handled by the flow divider, not the nozzles themselves.

B. The fuel level in the bowl will be too high, causing an overly rich mixture and possible fuel leakage

A float level set too high allows the fuel level in the float bowl to rise above the correct point, which increases fuel delivery to the discharge nozzle and produces an excessively rich mixture; it can also cause fuel to leak from the vents or discharge nozzle.

D. It introduces raw fuel into the engine oil supply just before shutdown to thin the oil, which evaporates out after the next start warms the engine

An oil dilution system introduces raw gasoline into the engine oil supply just before engine shutdown in cold weather. This thins the oil, making it easier to circulate for the next cold start. As the engine warms up after starting, the gasoline evaporates out of the oil, restoring normal viscosity.

D. Hot start

A hot start occurs when excess fuel is introduced relative to the available airflow during start, causing EGT to exceed limits before the engine reaches self-sustaining speed. The technician must abort the start immediately to prevent turbine damage.

D. Lead fouling from prolonged low-power ground operation; correct by leaning the mixture during ground operations and periodically clearing the engine with a brief power application

Extended low-power ground operation with a rich idle mixture allows lead bromide deposits (from the tetraethyl lead in avgas) to build up on spark plug electrodes, causing intermittent misfire; the standard correction is to lean the mixture during ground operations per the AFM and periodically run the engine up briefly to help clear the deposits.

D. Oil bypasses the cooler entirely, preventing it from being cooled

The Vernatherm valve normally routes cold oil around (bypasses) the oil cooler until it reaches operating temperature, then redirects oil through the cooler core as it expands. If the valve sticks in the bypass position, oil continues to bypass the cooler even when hot, so it never gets cooled, resulting in the high oil temperature observed with normal oil pressure since flow to the engine is unaffected.

C. Formation of fuel vapor in the lines that could interrupt fuel flow

High altitude combined with high temperatures lowers the boiling point margin of fuel, increasing the risk of vapor forming in fuel lines. The boost pump maintains positive fuel line pressure, keeping fuel in liquid form and ensuring uninterrupted flow to the engine-driven pump and injectors.

D. 9.5:1

Compression ratio = (swept volume + clearance volume) / clearance volume = (85 + 10) / 10 = 95/10 = 9.5:1.

C. The fuel control automatically limits thrust output so that full rated thrust is available at OATs up to 30°C, after which available thrust decreases as temperature rises further

Flat rating means the fuel control unit limits fuel flow (and thus thrust) so that the engine produces its full rated thrust across a range of ambient temperatures up to the flat-rated temperature. Above that temperature, air density decreases enough that the engine can no longer maintain rated thrust without exceeding internal temperature limits, so available thrust decreases.

B. A transformer-rectifier charges a storage capacitor, which is then discharged through a trigger transformer to the igniter plug in a single high-energy pulse

In a capacitor discharge ignition (CDI) exciter unit, input power (AC or DC) is stepped up and rectified to charge a storage capacitor to a high voltage; when a triggering circuit fires, the capacitor rapidly discharges through a trigger transformer, delivering a very high-energy, high-voltage pulse to the igniter plug. This design is used on turbine engines because it produces a much higher energy spark than a magneto, necessary to ignite fuel reliably under adverse conditions such as altitude, cold, or wet starts. Magnetos (with rotating magnets and breaker points) and impulse couplings are reciprocating engine ignition components, not part of turbine CD ignition systems.

D. A plunger and check valve arrangement using engine oil pressure to take up clearance

A hydraulic lifter uses a spring-loaded plunger inside a cylinder body with a one-way check valve; engine oil under pressure fills the chamber beneath the plunger, which extends to take up all valve train clearance (zero lash) and maintains it automatically as parts wear or thermally expand.

A. Rotating the crankshaft to the manufacturer's specified degrees before top dead center on the compression stroke, then adjusting the magneto position until the breaker points just begin to open

External (engine-to-magneto) timing is performed by rotating the crankshaft to the specified number of degrees before top dead center on the compression stroke for the timing cylinder, then rotating the magneto housing on the engine until the breaker points just begin to open (often indicated by a timing light), and securing the magneto in that position.

B. It allows the pilot to choose which tank or combination of tanks supplies fuel to each engine

The fuel selector valve is a manually (or electrically) operated valve that lets the pilot direct fuel flow from a chosen tank, both tanks, or the off position to the engine(s). Filtering, pressure regulation, and venting are performed by other components.

B. File the ring ends to slightly increase the end gap to meet the minimum specification

Insufficient ring end gap can cause the ring ends to butt together as the ring expands from heat during operation, leading to scuffing, scoring, or a stuck/broken ring. The correct correction is to carefully file the ring ends to open the gap to at least the minimum specified value.

B. Reduced oil tank pressure may allow the oil pump to cavitate, resulting in inadequate lubrication, especially at altitude or high power

Turbine engine oil tanks are often pressurized with bleed air to ensure a positive head of pressure at the oil pump inlet, preventing pump cavitation and foaming, especially during high-altitude or high-power operation. If the pressurization valve fails closed, the tank pressure drops, increasing the risk of pump cavitation and inadequate lubrication.

B. It reduces the risk of high-voltage leakage or flashover through the ignition harness at high altitude

In a low-tension system, only low voltage is carried through the distributor and harness to individual step-up coils located near each spark plug, where the voltage is stepped up just before the plug. This reduces the length of high-voltage wiring exposed to reduced air density at altitude, minimizing flashover and insulation breakdown. It still uses spark plugs, still may use an impulse coupling, and does not inherently produce higher voltage overall.

A. Fuel was introduced too early or in excessive quantity relative to the available airflow through the engine

A hot start occurs when the fuel-to-air ratio is too rich during light-off, typically from introducing fuel too soon (before sufficient airflow is established by the starter/compressor) or from excessive fuel flow, causing the flame temperature and EGT to rise rapidly beyond limits before enough airflow can cool the gas path. Excess starter energy or open bleed valves would tend to increase airflow and reduce hot start risk, and continuous igniter operation does not by itself cause overtemperature.

A. A freewheeling clutch to disengage the starter and a shear section to protect against overtorque

The starter adapter contains a clutch (overrunning or friction type) that allows the starter to disengage automatically once the engine starts and accelerates past the starter's speed, and a shear section (shear pin/section) designed to fail if excessive torque is applied, protecting the starter and gear train from damage.