Powerplant Systems & Engine Overhaul Flashcards

What does 'spectrometric oil analysis' (SOAP) detect in aircraft engine maintenance?

Answer: Trace metal particles in engine oil that indicate wear of specific engine components

SOAP identifies and quantifies specific metallic elements in oil samples; elevated levels of iron, chromium, copper, or other metals indicate wear of the corresponding engine components.

An engine is returned to service after overhaul. During the test run, EGT is higher than normal but RPM and manifold pressure are normal. What is the MOST likely cause?

Answer: Mixture is running too rich, causing incomplete combustion and elevated exhaust temperatures

An over-rich mixture results in incomplete combustion with excess unburned fuel entering the exhaust, elevating EGT; with normal power output (RPM/MP), the fuel/air ratio is the most likely variable.

What is the purpose of 'lapping' valves during engine overhaul?

Answer: Create a precise, gas-tight seal between the valve face and the valve seat

Lapping uses fine abrasive compound to create a matched, gas-tight contact surface between the valve face and seat, ensuring no compression or combustion gases escape past the valve.

What is the primary reason aircraft reciprocating engines use sodium-filled exhaust valves?

Answer: Liquid sodium inside the valve transfers heat from the valve head to the stem, cooling the valve

Liquid sodium moves back and forth inside the hollow valve stem as the engine runs, conducting heat from the hot valve head to the cooler stem and valve guide, preventing valve burning.

During turbine engine inspection, 'creep' damage on turbine blades is characterized by:

Answer: Permanent elongation of the blade caused by sustained high temperature and centrifugal stress

Turbine blade creep is the slow, permanent plastic deformation (elongation) that occurs when blades are subjected to high centrifugal loads at elevated temperatures over many operating hours.

What must be done before reinstalling a propeller flange nut after engine overhaul?

Answer: Verify the flange mating surfaces are clean, check the nut's thread condition, and torque to the manufacturer's specified value with a calibrated torque wrench

The propeller flange nut must be torqued to manufacturer specification with a calibrated torque wrench after verifying clean mating surfaces; incorrect torque can lead to propeller separation.

What is the function of a fuel control unit (FCU) on a turbine engine?

Answer: Meter fuel flow to maintain the scheduled fuel-to-air ratio across all power settings and environmental conditions

The FCU (also called a fuel metering unit) continuously adjusts fuel flow to match engine demands, compensating for changes in throttle position, altitude, airspeed, and inlet temperature to prevent surge, stall, or overtemp.