In a gas turbine engine, which section is responsible for raising the pressure of the incoming air before it reaches the combustion section?
ACS code: AM.III.B
Correct answer: The compressor section
Rationale: In a gas turbine engine the compressor section draws in air and increases its pressure, delivering high-pressure air to the combustion section where fuel is added and burned. The turbine section extracts energy from the expanding gases to drive the compressor, and the exhaust section directs spent gases overboard. Only the compressor raises the pressure of the incoming air, which is why it is sometimes described as the heart of the engine's airflow path.
Which type of compressor uses a series of rotating and stationary blade rows to compress air in stages along the engine axis?
ACS code: AM.III.B
Correct answer: Axial-flow compressor
Rationale: An axial-flow compressor moves air parallel to the engine's axis through alternating rows of rotating blades (rotors) and stationary blades (stators), with each rotor-stator pair forming a stage that adds a small pressure rise. A centrifugal compressor instead slings air radially outward with an impeller. Reverse-flow describes a combustor arrangement, not a compressor type.
Which combustion chamber design consists of individual cans, each with its own liner and outer case, arranged around the engine?
ACS code: AM.III.B
Correct answer: Can (multiple-can) type
Rationale: The can-type combustor uses several separate cylindrical chambers, each with an individual perforated liner inside its own outer housing, spaced around the engine. The annular type uses a single continuous combustion chamber surrounding the engine axis. The reverse-flow turbine choice is not a combustor classification, so the multiple individual chambers describe the can type.
What is the purpose of the turbine nozzle (turbine inlet guide vanes) located ahead of the first-stage turbine wheel?
ACS code: AM.III.B
Correct answer: To accelerate and direct gases onto the turbine blades at the correct angle
Rationale: The turbine nozzle, made up of stationary inlet guide vanes, forms convergent passages that accelerate the hot gases and turn them so they strike the turbine blades at the optimum angle for maximum energy transfer. Compression happens in the compressor, and extracting shaft power is the rotating turbine wheel's job, so the nozzle's role is to prepare and aim the gas flow.
On a turbofan engine, the fan moves a large mass of air that bypasses the engine core. What is this airflow called?
ACS code: AM.III.B
Correct answer: Bypass air
Rationale: In a turbofan, the fan accelerates a large volume of air, much of which passes around the engine core through the bypass duct rather than through the combustion section; this is the bypass air and it produces a substantial portion of the engine's thrust. Bleed air is tapped from the compressor for other uses, and primary combustion air passes through the core, so the air going around the core is bypass air.
A turbine engine fails to reach idle speed and stabilizes at a low rpm during start with normal lightoff. What starting malfunction does this describe?
ACS code: AM.III.B
Correct answer: Hung start
Rationale: A hung start occurs when the engine lights off normally but fails to accelerate to idle rpm, stabilizing at a lower-than-normal speed, typically due to insufficient starter assistance or inadequate power. A hot start involves exhaust temperature exceeding limits, and a wet (false) start is a failure to light off after fuel is introduced, so a normal lightoff that stalls below idle is a hung start.
In a free-turbine (free-power-turbine) turboshaft or turboprop engine, the power turbine
ACS code: AM.III.B
Correct answer: has no mechanical connection to the compressor and is driven only by the gas stream.
Rationale: In a free-turbine engine, the power turbine is driven aerodynamically by the hot gas stream from the gas generator but has no mechanical shaft coupling to the compressor spool. It can therefore rotate independently of the gas generator, with no clutch or freewheel link between the two, per FAA-H-8083-32 turbine engine fundamentals.