Why is carbon monoxide a concern with exhaust shroud cabin heat?

Cabin heat is taken from air warmed by flowing over a hot exhaust component inside a shroud. A crack or leaking joint under that shroud sends exhaust gas straight into the air entering the cabin, and carbon monoxide is colorless and odorless, so the occupants get no warning. That is why shroud-area inspection and leak checks are taken seriously.

How does a thrust reverser work?

It redirects the gas stream forward rather than reversing anything mechanically inside the engine, which keeps rotating in its normal direction. A mechanical blockage design drops clamshell or target doors into the exhaust path behind the nozzle so the gas is turned forward. An aerodynamic design closes blocker doors in the fan duct and routes fan air through forward-angled cascade vanes.

Where are EGT thermocouples located on a turbine engine?

Exhaust gas temperature probes sit in the gas path aft of the turbine, spaced around the duct so the indication averages several probes instead of following one hot spot. Engines that display turbine inlet or interstage temperature place their probes further upstream, which is why two similar-looking gauges can be measuring completely different stations.

Which engines are most likely to have exhaust noise suppressors?

Noise output rises steeply with jet velocity, so turbojets and low-bypass engines, whose exhaust leaves at very high velocity, are the ones fitted with suppression hardware. A high-bypass turbofan surrounds its hot core stream with a much slower fan stream that does most of the mixing on its own, greatly reducing the need for a separate suppressor.

What is the exhaust cone for?

Gas leaving the last turbine stage is still swirling. The exhaust cone and its support struts straighten that flow into a solid jet and cut turbulence, and the annular passage between the cone and the outer duct is divergent, so gas velocity drops and static pressure rises slightly before the flow reaches the tail pipe and nozzle.

Why is carbon monoxide contamination of cabin air a concern with exhaust-shroud heating systems?

A crack in the exhaust can allow gases to enter the heated cabin air

Carbon monoxide forms only when the cabin heat valve is fully closed

The shroud chemically converts oxygen into carbon monoxide gas

In a turbine engine, the convergent exhaust nozzle is used primarily to:

Increase the velocity of the exhaust gases as they leave the engine

Decrease the velocity of the gases to recover static pressure

Cool the exhaust gases before they reach the tailpipe section

What is the primary purpose of the exhaust cone (tail cone) located at the rear of a turbine engine exhaust section?

To smooth the gas flow and reduce turbulence at the turbine exit

To ignite unburned fuel remaining in the exhaust stream

To add swirl to the gas flow to improve combustion stability

The exhaust gas temperature (EGT) thermocouples in a turbine engine are generally located:

In the turbine or exhaust section downstream of the combustion area

In the compressor inlet ahead of the first stage of blades

Inside the fuel manifold near the spray nozzle outlets

Turbine engine exhaust noise suppressors reduce noise primarily by:

Increasing the gas perimeter to mix exhaust quickly with ambient air

Raising the exhaust gas temperature to shift the noise frequency

Lowering the total mass of exhaust gas that the engine produces

A mechanical-blockage (clamshell) thrust reverser produces reverse thrust by:

Deploying doors into the gas stream to deflect it forward and outward

Opening louvers in the inlet to reduce the air entering the engine

Bleeding compressor air overboard to spoil the forward thrust

Stainless steel and similar exhaust components should not be marked with an ordinary lead pencil because:

Lead-pencil or zinc/lead-based marks can cause cracking when heated

Any surface marking instantly voids the component type certificate

Markings add measurable weight that unbalances the exhaust system

The function of the exhaust cone assembly of a turbine engine is to

straighten and collect the exhaust gases into a solid exhaust jet.

collect the exhaust gases and act as a noise suppressor.

swirl and collect the exhaust gases into a single exhaust jet.

To accelerate a gas from subsonic to supersonic velocity, the exhaust duct must be shaped

convergent first and then divergent along its length.

divergent first and then convergent along its length.

convergent only, choked at the largest end at Mach 1.

Untreated jet wake noise from a turbine engine exhaust is predominantly

low frequency at high decibel level.

low frequency at low decibel level.

high frequency at high decibel level.

Hot spots on the tail cone of a turbine engine are possible indicators of a malfunctioning fuel nozzle or

an improperly positioned tail cone.

Placing an exhaust cone aft of the turbine in a turbine engine causes the pressure in the first part of the exhaust duct to

increase as the gas velocity decreases.

decrease as the gas velocity increases.

increase as the gas velocity also increases.

A convergent-divergent exhaust nozzle is used on a high-pressure-ratio engine in order to

make maximum use of pressure thrust.

require the aircraft to be traveling at supersonic speed.

produce a separate type of thrust known as kinetic thrust.

The jet pipe (exhaust duct) of a gas turbine engine

protects the airframe from heat damage.

has an inner cone that protects the rear turbine disk.

is convergent to increase gas velocity as much as possible.

For what purpose is the propelling (exhaust) nozzle of a gas turbine engine designed?

To increase the velocity and decrease the pressure of the exiting gas stream.

To increase both the velocity and pressure of the exiting gas stream.

To decrease the velocity and increase the pressure of the exiting gas stream.

If the exit area of an exhaust nozzle is too large, the result is

a lower exit velocity, causing a loss of thrust.

a lower exit velocity, with negligible effect on thrust.

choking of the nozzle at a lower gas temperature.

The exhaust section of a gas turbine engine is designed to

impart a high exit velocity to the exhaust gases.

increase temperature, thereby increasing velocity.

decrease temperature, thereby decreasing pressure.

Reverse thrust can only be selected when the throttle is

in the wide-open (takeoff) position.

at the 75 percent power position.

A convergent-divergent exhaust nozzle is designed to

make maximum use of pressure thrust.

operate only when the aircraft is traveling at supersonic speeds.

produce a distinct form of thrust known as kinetic thrust.

Jet exhaust noise can be reduced by

increasing the rate at which the jet mixes with ambient air.

lowering the vibration frequency of the exhaust.

increasing the jet exhaust velocity.

Operating thrust reversers at low ground speeds can sometimes cause

foreign-object ingestion, hot-gas re-ingestion, and compressor stalls.

hot-gas re-ingestion and compressor stalls only.

foreign-object ingestion and hot-gas re-ingestion only.

The purpose of the cascade vanes in a thrust reversing system is to

turn the fan and/or hot gases blocked from the exhaust nozzle to a forward direction.

form a solid blocking door across the jet exhaust path.

turn the exhaust gases forward just after they exit the nozzle.

A simple convergent exhaust nozzle produces mainly

equal momentum and pressure thrust.

With the thrust reverser system deployed, the rearward thrust an engine can produce is

less than its forward thrust capability.

equal to or less than forward, depending on ambient conditions.

equal to its forward thrust capability.

Which statement is generally true regarding thrust reverser systems?

It is possible to move some aircraft backward on the ground using reverse thrust.

Thrust reversers on the same aircraft must always be operated simultaneously and cannot operate independently.

Mechanical blocking systems permit deployment only aft of the exhaust nozzle.

What is the proper operating sequence when using thrust reversers to slow an aircraft after landing?

Retard thrust levers to ground idle, raise the thrust reverser levers as required, then retard the reverser levers to ground idle.

Select reverse, advance the reverser levers no higher than 75 percent N1, then retard them to idle near normal taxi speed.

Advance thrust levers toward takeoff as required, select reverse, deselect reverse, then retard thrust levers to ground idle.

Most exhaust system failures result from thermal fatigue cracking at areas of stress concentration. This cracking is usually caused by

the high temperatures at which the exhaust system operates.

improper welding techniques used during manufacture.

the drastic temperature changes encountered at high altitude.

Thrust reversal on a high-bypass turbofan engine is normally achieved using

blocker doors and cascade vanes.

a clamshell-door configuration.

If damage is found to thrust reverser cascade vanes and they must be replaced, the technician must

replace the vanes only with new ones of the correct part number for that position.

replace the damaged vanes with standard 45-degree vanes.

interchange the cascade vanes freely, since they are interchangeable.

What flight-deck indication confirms to the crew that the thrust reversers have deployed?

A sequence of position indicator lights.

A sudden feeling of rapid deceleration.

An audible warning horn in the cockpit.

The purpose of a convergent propelling (exhaust) nozzle on a turbojet engine is to

increase the velocity of the gas to increase thrust.

direct the gas flow onto the turbine blades.

decrease exhaust velocity to raise static pressure.

If a thrust reverser is left deployed below the normal stow speed during the landing roll,

hot exhaust gases can be reingested into the engine inlet.

the reverser becomes completely ineffective at all speeds.

a high EGT automatically restows the reverser doors.

The physical size of a turbine engine's exhaust section is primarily dictated by the

size and installed location of the engine.

size and location of the diffuser cone only.

size of the engine alone, regardless of location.

Acoustic linings made from composite materials are used in which section of a turbine engine?

The cold (fan and inlet) section only.

Both the hot and the cold sections.

The hot (exhaust) section only.

Fibrous metallic lining used for noise suppression is installed

in the hot (exhaust) area of the engine.

in the cold (fan and inlet) area of the engine.

only within lobe-type exhaust noise suppressors.

Acoustic noise-suppression lining in the fan area of a turbofan is typically constructed from a

porous (perforated) facing over a honeycomb core with a backing sheet.

layer of felt bonded to an aluminum sheet.

stack of bonded resin layers over a solid skin.

Acoustic blankets are installed on a turbine engine installation primarily to

reduce the noise levels radiating from the engine.

increase the thermal efficiency of the engine.

improve the aerodynamic streamlining of the engine.

A convergent propelling (exhaust) nozzle operating in a choked condition produces

Both pressure thrust and velocity (momentum) thrust

Pressure thrust only, with no momentum thrust

Velocity (momentum) thrust only, with no pressure thrust

Engine Exhaust and Reverser Systems — FAA A&P Test Questions (ACS AM.III.L)

Engine Exhaust and Reverser Systems covers two very different worlds under one heading. On reciprocating engines it is stacks, collectors, mufflers, heat exchangers, and the carbon monoxide risk that comes with using exhaust heat for the cabin. On turbines it is the exhaust cone, tail pipe, nozzle shape, exhaust gas temperature sensing, noise suppression, and thrust reversers. Expect inspection and materials questions as well, because exhaust components are high-temperature alloys that carry their own handling rules.

Written by the AMTprep editorial team · Published July 27, 2026 · Last reviewed October 21, 2026

Written against the FAA primary sources cited at the foot of this page.

What ACS AM.III.L covers

On the reciprocating side, the exam wants you to see a cabin heat system for what it is: a heat exchanger wrapped around a live exhaust component. Any crack, loose slip joint, or blown gasket inside that shroud can push exhaust gas — including colorless, odorless carbon monoxide — into the cabin air supply, which is why exhaust inspection is careful, repetitive work. You look for stains, bulges, and cracks at welds and clamps, and you inspect or leak-check the shrouded area rather than assuming it is sound. 14 CFR Part 43 Appendix D lists exhaust stacks among the items covered during annual and 100-hour inspections. On the turbine side, FAA-H-8083-32 covers the exhaust section: the exhaust cone and its support struts straighten the swirling gas leaving the last turbine stage into a solid, usable jet and reduce turbulence, and the passage formed between the cone and the outer duct slows the gas and recovers pressure ahead of the tail pipe. The nozzle then turns that pressure back into velocity — a convergent nozzle accelerates subsonic gas to produce thrust, while a convergent-divergent nozzle is used where the flow must go supersonic. Exhaust gas temperature is sampled by thermocouple probes in the gas stream downstream of the turbine, and you should know how that location differs from turbine inlet or interstage sensing. Noise suppression and thrust reversers close the area out, together with the handling rules for stainless and nickel alloy exhaust parts.

Where this sits on the test

ACS AM.III.L is tested on the FAA Powerplant written test, one of 1,353 ACS-tagged questions in the Powerplant bank. Every question tagged to this area carries a worked rationale and its FAA handbook reference, so you can drill the code itself rather than the whole test.

FAA handbook references

FAA-H-8083-32

Three traps candidates fall into

Bernoulli gets applied backwards at the tail pipe. In subsonic flow a convergent exhaust nozzle speeds the gas up and drops its pressure, which is what produces thrust; the divergent shape is the one that slows gas and raises pressure. Candidates who memorized the inlet diffuser rule routinely reverse this.
Noise suppressors are pictured as mufflers that soak up sound. They work by breaking the exhaust into smaller streams that mix quickly with the surrounding air, shifting the energy toward higher frequencies that the atmosphere attenuates faster and the ear finds less objectionable, rather than by absorbing sound energy.
Marking an exhaust part with an ordinary lead pencil looks harmless. The graphite leaves carbon on the surface, and at exhaust temperatures that carbon migrates into stainless and nickel alloys and causes local embrittlement and cracking. Use only the marking media the manufacturer approves for high-temperature alloys.

49 free sample questions from ACS AM.III.L

AM.III.LTap an answer
Why is carbon monoxide contamination of cabin air a concern with exhaust-shroud heating systems?
Show the answer and explanation
Answer: A crack in the exhaust can allow gases to enter the heated cabin air
Why: Because the cabin air is heated by passing through a shroud in direct contact with the hot exhaust, a crack or leak in the muffler or stack lets exhaust gas, which contains carbon monoxide, mix into the air being ducted to the cabin. This is why exhaust integrity is critical on shroud-heated aircraft. Carbon monoxide is a product of combustion in the engine, not created by the heat valve position or by the shroud altering oxygen.· FAA-H-8083-32 — Exhaust system inspection / CO hazard
AM.III.LTap an answer
In a turbine engine, the convergent exhaust nozzle is used primarily to:
Show the answer and explanation
Answer: Increase the velocity of the exhaust gases as they leave the engine
Why: A convergent exhaust nozzle has a decreasing cross-sectional area, which accelerates the subsonic exhaust gas and increases its velocity as it exits, converting pressure energy into kinetic energy to produce thrust. A divergent shape would be used to recover pressure or to handle supersonic flow; the convergent nozzle is not a cooling device.· FAA-H-8083-32 — Turbine engine exhaust nozzles
AM.III.LTap an answer
What is the primary purpose of the exhaust cone (tail cone) located at the rear of a turbine engine exhaust section?
Show the answer and explanation
Answer: To smooth the gas flow and reduce turbulence at the turbine exit
Why: The exhaust cone, supported by struts in the exhaust collector, fills the center of the gas path behind the turbine to convert turbulent flow into a smoother, more uniform stream and to prevent the gases from flowing across the rear face of the turbine disk. Adding swirl is undesirable in the exhaust, and the cone does not ignite fuel.· FAA-H-8083-32 — Turbine exhaust section (exhaust cone and struts)
AM.III.LTap an answer
The exhaust gas temperature (EGT) thermocouples in a turbine engine are generally located:
Show the answer and explanation
Answer: In the turbine or exhaust section downstream of the combustion area
Why: EGT (or turbine inlet/interstage temperature) thermocouples are positioned in the hot section, in or just aft of the turbine where gas temperatures can be measured to monitor engine operating limits. Placing them in the cold compressor inlet or in the fuel manifold would not provide a meaningful indication of turbine operating temperature.· FAA-H-8083-32 — Exhaust section / EGT measurement
AM.III.LTap an answer
Turbine engine exhaust noise suppressors reduce noise primarily by:
Show the answer and explanation
Answer: Increasing the gas perimeter to mix exhaust quickly with ambient air
Why: Jet exhaust noise is largely caused by the high-velocity exhaust shearing against still ambient air. Noise suppressors (such as multi-tube and corrugated/lobed designs) break the single large exhaust stream into many smaller streams, increasing the perimeter of contact so the high-velocity gas mixes more rapidly with surrounding air. This reduces the low-frequency noise. Suppressors do not reduce gas mass or rely on raising temperature.· FAA-H-8083-32 — Turbine engine noise suppression
AM.III.LTap an answer
A mechanical-blockage (clamshell) thrust reverser produces reverse thrust by:
Show the answer and explanation
Answer: Deploying doors into the gas stream to deflect it forward and outward
Why: A mechanical-blockage reverser uses movable clamshell-type doors that swing into the exhaust gas stream behind the engine, physically blocking the rearward flow and deflecting the gases forward and outward at an angle to create reverse thrust. Reverse thrust comes from redirecting the exhaust, not from bleeding compressor air or restricting the inlet.· FAA-H-8083-32 — Thrust reversers (mechanical-blockage/clamshell type)
AM.III.LTap an answer
Stainless steel and similar exhaust components should not be marked with an ordinary lead pencil because:
Show the answer and explanation
Answer: Lead-pencil or zinc/lead-based marks can cause cracking when heated
Why: Marking high-temperature exhaust alloys with a common lead pencil or with zinc- or lead-based materials can lead to intergranular embrittlement and cracking when the part reaches operating temperature, because these elements penetrate the hot metal. Approved layout dye or chalk should be used instead. The concern is metallurgical damage, not certificate validity or weight.· FAA-H-8083-32 — Exhaust system materials and repair precautions
AM.III.LTap an answer
Of the following, which engine type is most likely to have an exhaust noise-suppression unit installed?
Show the answer and explanation
Answer: A turbojet.
Why: A turbojet exhausts a high-velocity jet, and the large shear between that jet and the surrounding air is the main noise source, so it most often needs an exhaust noise suppressor. Turboprops and turboshafts expel lower-velocity gas streams and are inherently quieter at the exhaust.· FAA-H-8083-32 — Engine Exhaust and Reverser Systems
AM.III.LTap an answer
In a turbojet engine, the exhaust (propelling) nozzle is located in which section?
Show the answer and explanation
Answer: Exhaust
Why: The propelling nozzle forms the rear of the exhaust section, where the gases are accelerated to produce thrust. The turbine extracts shaft power upstream of it, and combustion occurs farther forward, so the nozzle is not located in those sections.· FAA-H-8083-32 — Engine Exhaust and Reverser Systems
AM.III.LTap an answer
The reverse thrust developed by a typical thrust reverser at full reverse power is approximately
Show the answer and explanation
Answer: 50% of forward thrust.
Why: Thrust reversers redirect only part of the exhaust or fan flow and do so at an angle, so the rearward-acting force recovered is roughly half of the forward thrust the engine produces at the same setting. Full reverse power is therefore approximately 50% of forward thrust.· FAA-H-8083-32 — Engine Exhaust and Reverser Systems
AM.III.LTap an answer
The function of the exhaust cone assembly of a turbine engine is to
Show the answer and explanation
Answer: straighten and collect the exhaust gases into a solid exhaust jet.
Why: The exhaust cone assembly straightens the swirling gas leaving the turbine and gathers it into a smooth, solid jet, while its struts also support the cone. This recovers residual swirl energy; it is not designed to add swirl or to act primarily as a noise suppressor.· FAA-H-8083-32 — Engine Exhaust and Reverser Systems
AM.III.LTap an answer
What is the maximum practical angle through which the gas flow can be turned during thrust reversal?
Show the answer and explanation
Answer: About 135 degrees.
Why: In practice the gas flow in a thrust reverser cannot be turned a full 180 degrees because the cascade and deflector cannot reverse it completely; the practical limit is around 135 degrees. The remaining forward component is why reverse thrust is always less than full forward thrust.· FAA-H-8083-32 — Engine Exhaust and Reverser Systems
AM.III.LTap an answer
To accelerate a gas from subsonic to supersonic velocity, the exhaust duct must be shaped
Show the answer and explanation
Answer: convergent first and then divergent along its length.
Why: To accelerate a gas from subsonic to supersonic speed the duct must first converge to reach Mach 1 at the throat and then diverge to continue accelerating the now-supersonic flow. This convergent-divergent (con-di) shape is the defining feature of a supersonic nozzle.· FAA-H-8083-32 — Engine Exhaust and Reverser Systems
AM.III.LTap an answer
Untreated jet wake noise from a turbine engine exhaust is predominantly
Show the answer and explanation
Answer: low frequency at high decibel level.
Why: Untreated jet wake noise comes from the violent mixing of the high-velocity exhaust with the surrounding air, producing predominantly low-frequency sound at high sound-pressure levels. Suppressors break the wake into smaller streams to shift energy toward less troublesome higher frequencies.· FAA-H-8083-32 — Engine Exhaust and Reverser Systems
AM.III.LTap an answer
Hot spots on the tail cone of a turbine engine are possible indicators of a malfunctioning fuel nozzle or
Show the answer and explanation
Answer: a faulty combustion chamber.
Why: A localized hot spot on the tail cone indicates an uneven temperature pattern in the gas, which points to a malfunctioning fuel nozzle or a faulty (cracked or burned) combustion chamber distorting the flame and gas distribution. An igniter or the tail cone position would not produce a localized hot streak.· FAA-H-8083-32 — Engine Exhaust and Reverser Systems
AM.III.LTap an answer
Placing an exhaust cone aft of the turbine in a turbine engine causes the pressure in the first part of the exhaust duct to
Show the answer and explanation
Answer: increase as the gas velocity decreases.
Why: The exhaust cone makes the gas passage divergent in its first part, so the gas slows and, by Bernoulli's principle, its static pressure rises. Raising the static pressure ahead of the propelling nozzle helps the nozzle produce thrust efficiently.· FAA-H-8083-32 — Engine Exhaust and Reverser Systems
AM.III.LTap an answer
A convergent-divergent exhaust nozzle is used on a high-pressure-ratio engine in order to
Show the answer and explanation
Answer: make maximum use of pressure thrust.
Why: A convergent-divergent nozzle allows the gas to keep expanding to near-ambient pressure in the divergent section, extracting the maximum pressure thrust from a high-pressure-ratio engine. It does not require the aircraft to be supersonic, and the thrust it produces is not a separate kinetic type.· FAA-H-8083-32 — Engine Exhaust and Reverser Systems
AM.III.LTap an answer
The jet pipe (exhaust duct) of a gas turbine engine
Show the answer and explanation
Answer: protects the airframe from heat damage.
Why: The exhaust duct carries the hot gas to the propelling nozzle and is shielded so it protects the surrounding airframe structure from the high exhaust temperatures. The inner cone is part of the exhaust cone assembly and serves a different purpose (FAA-H-8083-32, Engine Exhaust and Reverser Systems).· FAA-H-8083-32 — Engine Exhaust and Reverser Systems
AM.III.LTap an answer
For what purpose is the propelling (exhaust) nozzle of a gas turbine engine designed?
Show the answer and explanation
Answer: To increase the velocity and decrease the pressure of the exiting gas stream.
Why: A convergent propelling nozzle converts the gas stream's pressure energy into kinetic energy, so the gas leaves at increased velocity and reduced pressure, and this high exit velocity produces thrust. Pressure and velocity cannot both rise together in a simple converging nozzle (FAA-H-8083-32, Engine Exhaust and Reverser Systems).· FAA-H-8083-32 — Engine Exhaust and Reverser Systems
AM.III.LTap an answer
If the exit area of an exhaust nozzle is too large, the result is
Show the answer and explanation
Answer: a lower exit velocity, causing a loss of thrust.
Why: If the nozzle exit area is too large the gas over-expands and leaves at a lower exit velocity. Since thrust depends on jet velocity, this produces a loss of thrust — a significant, not negligible, effect (FAA-H-8083-32, Engine Exhaust and Reverser Systems).· FAA-H-8083-32 — Engine Exhaust and Reverser Systems
AM.III.LTap an answer
A choked exhaust nozzle
Show the answer and explanation
Answer: increases thrust.
Why: When a nozzle is choked the throat reaches Mach 1 and a residual pressure difference exists across the nozzle exit; this pressure thrust adds to the momentum thrust, so total thrust increases. A choked nozzle is a normal high-power condition, not a loss (FAA-H-8083-32, Engine Exhaust and Reverser Systems).· FAA-H-8083-32 — Engine Exhaust and Reverser Systems
AM.III.LTap an answer
The exhaust section of a gas turbine engine is designed to
Show the answer and explanation
Answer: impart a high exit velocity to the exhaust gases.
Why: The exhaust (propelling nozzle) section converts the remaining pressure energy into kinetic energy, imparting a high exit velocity to the gas, which generates jet thrust. It is not designed merely to raise or lower temperature (FAA-H-8083-32, Engine Exhaust and Reverser Systems).· FAA-H-8083-32 — Engine Exhaust and Reverser Systems
AM.III.LTap an answer
Reverse thrust can only be selected when the throttle is
Show the answer and explanation
Answer: in the closed (idle) position.
Why: For safety, reverse thrust can only be selected with the throttle closed (at idle) so the reverser deploys against low engine power before reverse thrust is increased. Deploying at high power risks reverser damage and uncontrolled forces (FAA-H-8083-32, Engine Exhaust and Reverser Systems).· FAA-H-8083-32 — Engine Exhaust and Reverser Systems
AM.III.LTap an answer
A convergent-divergent exhaust nozzle is designed to
Show the answer and explanation
Answer: make maximum use of pressure thrust.
Why: A convergent-divergent nozzle lets the gas keep expanding toward ambient pressure in its divergent section, extracting maximum pressure thrust from a high pressure-ratio engine. It does not require the aircraft itself to be supersonic, and its thrust is not a separate kinetic type (FAA-H-8083-32, Engine Exhaust and Reverser Systems).· FAA-H-8083-32 — Engine Exhaust and Reverser Systems
AM.III.LTap an answer
On forward-fan turbofan engines, thrust reversal is normally obtained by reversing the
Show the answer and explanation
Answer: cold (fan) stream.
Why: On forward-fan engines the bypass (cold) airflow is the dominant thrust producer, so reversers redirect the cold fan stream forward to generate reverse thrust. The hot core stream is usually left to exhaust normally because its contribution is comparatively small and its high temperature complicates reversal hardware (FAA-H-8083-32, Engine Exhaust and Reverser Systems).· FAA-H-8083-32 — Engine Exhaust and Reverser Systems
AM.III.LTap an answer
Jet exhaust noise can be reduced by
Show the answer and explanation
Answer: increasing the rate at which the jet mixes with ambient air.
Why: Jet exhaust noise comes from the violent shearing between the high-velocity gas and the still ambient air. Promoting faster mixing of the jet with the surrounding air smooths this velocity gradient and lowers noise. Increasing jet velocity raises noise, since acoustic power increases steeply with exhaust speed (FAA-H-8083-32, Engine Exhaust and Reverser Systems).· FAA-H-8083-32 — Engine Exhaust and Reverser Systems
AM.III.LTap an answer
Operating thrust reversers at low ground speeds can sometimes cause
Show the answer and explanation
Answer: foreign-object ingestion, hot-gas re-ingestion, and compressor stalls.
Why: At low ground speed the reversed efflux is no longer carried clear of the inlet, so it can recirculate into the engine. This causes hot gas re-ingestion (raising inlet temperature), stirs up sand and debris for foreign-object ingestion, and the disturbed, hot inlet air can trigger compressor stalls. All three effects can occur (FAA-H-8083-32, Engine Exhaust and Reverser Systems).· FAA-H-8083-32 — Engine Exhaust and Reverser Systems
AM.III.LTap an answer
The purpose of the cascade vanes in a thrust reversing system is to
Show the answer and explanation
Answer: turn the fan and/or hot gases blocked from the exhaust nozzle to a forward direction.
Why: Once the blocker doors close off the normal rearward path, the diverted airflow must be turned forward to produce reverse thrust. The cascade vanes are the curved vane grid that redirects this blocked fan and/or hot gas flow forward and outward, creating the rearward-acting reverse-thrust component (FAA-H-8083-32, Engine Exhaust and Reverser Systems).· FAA-H-8083-32 — Engine Exhaust and Reverser Systems
AM.III.LTap an answer
A simple convergent exhaust nozzle produces mainly
Show the answer and explanation
Answer: momentum thrust.
Why: A simple convergent nozzle accelerates the gas to produce thrust chiefly by the rate of change of momentum of the exhaust. Significant pressure thrust appears only when the nozzle is choked and a residual exit pressure exists; for a basic convergent nozzle the thrust is predominantly momentum thrust (FAA-H-8083-32, Engine Exhaust and Reverser Systems).· FAA-H-8083-32 — Engine Exhaust and Reverser Systems
AM.III.LTap an answer
With the thrust reverser system deployed, the rearward thrust an engine can produce is
Show the answer and explanation
Answer: less than its forward thrust capability.
Why: Reverse thrust is always a fraction of forward thrust because the cascades and blocker doors cannot turn the efflux fully forward, and typically only the fan stream is reversed at reduced efficiency. Reverse thrust is on the order of half of forward thrust, so it is less than the forward capability (FAA-H-8083-32, Engine Exhaust and Reverser Systems).· FAA-H-8083-32 — Engine Exhaust and Reverser Systems
AM.III.LTap an answer
Which statement is generally true regarding thrust reverser systems?
Show the answer and explanation
Answer: It is possible to move some aircraft backward on the ground using reverse thrust.
Why: Reverse thrust produces a genuine rearward force, and on some aircraft it is sufficient to overcome rolling resistance and move the aircraft backward (power-back). The practice is restricted because of re-ingestion and FOD risk, but it is physically possible (FAA-H-8083-32, Engine Exhaust and Reverser Systems).· FAA-H-8083-32 — Engine Exhaust and Reverser Systems
AM.III.LTap an answer
What is the proper operating sequence when using thrust reversers to slow an aircraft after landing?
Show the answer and explanation
Answer: Retard thrust levers to ground idle, raise the thrust reverser levers as required, then retard the reverser levers to ground idle.
Why: After touchdown the engines must first be at idle before reverse is selected, so the thrust levers are brought to ground idle, the reverser levers are then raised to apply reverse power as required, and finally returned to ground idle before taxi speed. Selecting reverse from a high power setting is not permitted (FAA-H-8083-32, Engine Exhaust and Reverser Systems).· FAA-H-8083-32 — Engine Exhaust and Reverser Systems
AM.III.LTap an answer
Most exhaust system failures result from thermal fatigue cracking at areas of stress concentration. This cracking is usually caused by
Show the answer and explanation
Answer: the high temperatures at which the exhaust system operates.
Why: The exhaust system runs continuously at very high gas temperatures and undergoes repeated thermal cycling. The resulting expansion and contraction sets up cyclic stresses at points of stress concentration, producing thermal-fatigue cracking. This normal high-temperature operating environment, not a manufacturing fault, is the usual cause (FAA-H-8083-32, Engine Exhaust and Reverser Systems).· FAA-H-8083-32 — Engine Exhaust and Reverser Systems
AM.III.LTap an answer
Thrust reversal on a high-bypass turbofan engine is normally achieved using
Show the answer and explanation
Answer: blocker doors and cascade vanes.
Why: High-bypass engines reverse only the large cold fan stream, using blocker doors that close the bypass duct and cascade vanes that turn the flow forward. Clamshell and bucket (target) doors are associated with low-bypass or turbojet engines that reverse the hot exhaust stream (FAA-H-8083-32, Engine Exhaust and Reverser Systems).· FAA-H-8083-32 — Engine Exhaust and Reverser Systems
AM.III.LTap an answer
If damage is found to thrust reverser cascade vanes and they must be replaced, the technician must
Show the answer and explanation
Answer: replace the vanes only with new ones of the correct part number for that position.
Why: Cascade vanes are designed with a specific turning angle and profile for that engine position and are not interchangeable; the discharge angle must be maintained. Replacements must be the correct approved part number for the position, since different-angle or non-matching vanes would alter the reverse-thrust pattern (FAA-H-8083-32, Engine Exhaust and Reverser Systems).· FAA-H-8083-32 — Engine Exhaust and Reverser Systems
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Lobe-type (corrugated) exhaust noise suppressors used in the hot exhaust stream of a turbine engine are made from
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Answer: heat-resistant alloy.
Why: Lobe (corrugated) noise suppressors sit directly in the hot exhaust efflux and must withstand high gas temperatures while holding their shape, so they are made from heat-resistant alloy. Ordinary steel would not survive the thermal environment, and composite materials are unsuitable for the raw exhaust stream (FAA-H-8083-32, Exhaust Systems).· FAA-H-8083-32 — Engine Exhaust and Reverser Systems
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What flight-deck indication confirms to the crew that the thrust reversers have deployed?
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Answer: A sequence of position indicator lights.
Why: Reverser deployment is monitored by position sensors that drive flight-deck indications, so the crew receives a sequence of lights (such as unlock and deployed indications) confirming the reverser state. Deceleration is felt rather than a positive indication, and a dedicated audible warning is not the normal deploy confirmation (FAA-H-8083-32, Thrust Reversers).· FAA-H-8083-32 — Engine Exhaust and Reverser Systems
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Through approximately what angle are the exhaust gases turned in a clamshell-type thrust reverser?
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Answer: About 135 degrees.
Why: A clamshell (hot-stream) reverser does not turn the gas fully forward; the doors deflect the efflux through about 135 degrees, giving a forward-and-outward component that produces reverse thrust while allowing the flow to clear the airframe. A full 180-degree turn is not achieved with this design (FAA-H-8083-32, Thrust Reversers).· FAA-H-8083-32 — Engine Exhaust and Reverser Systems
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The purpose of a convergent propelling (exhaust) nozzle on a turbojet engine is to
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Answer: increase the velocity of the gas to increase thrust.
Why: The propelling (exhaust) nozzle has a converging area that accelerates the gas as it leaves the engine. This rise in exhaust velocity increases the rate of change of momentum and therefore the thrust. It does not decelerate the flow, nor does it direct gas onto the turbines, which is the role of the turbine nozzle guide vanes (FAA-H-8083-32, Exhaust Nozzle).· FAA-H-8083-32 — Engine Exhaust and Reverser Systems
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If a thrust reverser is left deployed below the normal stow speed during the landing roll,
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Answer: hot exhaust gases can be reingested into the engine inlet.
Why: If reverse is left deployed below the speed at which the forward-directed efflux is carried clear, the hot reversed gases recirculate forward and are drawn back into the inlet. This hot-gas reingestion raises inlet temperature and can cause a compressor stall, which is why reversers are stowed before the aircraft slows too far (FAA-H-8083-32, Thrust Reversers).· FAA-H-8083-32 — Engine Exhaust and Reverser Systems
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The physical size of a turbine engine's exhaust section is primarily dictated by the
Show the answer and explanation
Answer: size and installed location of the engine.
Why: The exhaust section must match the gas flow leaving the engine and route it past the surrounding structure, so its dimensions are governed by both engine size, which sets the gas mass flow, and engine location/installation, which dictates the available space and ducting. Neither factor alone fully determines it (FAA-H-8083-32, Exhaust Systems).· FAA-H-8083-32 — Engine Exhaust and Reverser Systems
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Acoustic linings made from composite materials are used in which section of a turbine engine?
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Answer: The cold (fan and inlet) section only.
Why: Composite acoustic linings are fitted in the cold (fan, inlet, and bypass) sections, where temperatures are low enough for the bonded honeycomb materials to survive while absorbing fan noise. The hot section's high temperatures would damage composite linings, so they are not used there.· FAA-H-8083-32 — Engine Exhaust and Reverser Systems
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Fibrous metallic lining used for noise suppression is installed
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Answer: in the hot (exhaust) area of the engine.
Why: Fibrous metallic noise-suppression lining is used in the hot areas of the engine, such as the exhaust region, because metallic fibers tolerate the high temperatures that would destroy composite linings. Composite honeycomb acoustic panels are reserved for the cooler fan and inlet sections.· FAA-H-8083-32 — Engine Exhaust and Reverser Systems
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Acoustic noise-suppression lining in the fan area of a turbofan is typically constructed from a
Show the answer and explanation
Answer: porous (perforated) facing over a honeycomb core with a backing sheet.
Why: Acoustic lining in the cooler fan area is built from a porous (perforated) facing over a honeycomb core with a solid backing sheet, forming resonator cells that absorb fan noise. Simple resin layers or felt-and-aluminum constructions do not provide this tuned sound-absorbing structure.· FAA-H-8083-32 — Engine Exhaust and Reverser Systems
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Acoustic blankets are installed on a turbine engine installation primarily to
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Answer: reduce the noise levels radiating from the engine.
Why: Acoustic blankets are fitted specifically to absorb sound and reduce the noise levels radiating from the engine. They are not installed to improve thermal efficiency or to streamline the engine, which are unrelated functions.· FAA-H-8083-32 — Engine Exhaust and Reverser Systems
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A convergent propelling (exhaust) nozzle operating in a choked condition produces
Show the answer and explanation
Answer: Both pressure thrust and velocity (momentum) thrust
Why: Per FAA-H-8083-32, a propelling nozzle produces thrust from two components: the momentum (velocity) thrust of the accelerated gas leaving the nozzle, plus pressure thrust when the nozzle is choked and exit static pressure exceeds ambient. A choked propelling nozzle therefore delivers both pressure and velocity thrust, not one alone.· FAA-H-8083-32 — Engine Exhaust and Reverser Systems
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Reverse thrust can only be selected when the thrust lever (throttle) is
Show the answer and explanation
Answer: At the idle stop with forward power retarded
Why: Reverse thrust can only be selected with the thrust lever at the idle stop. This interlock prevents the reverser being deployed at high forward power, which could be hazardous; the lever must be brought to idle before the reverse mechanism can be engaged and reverse power then applied.· FAA-H-8083-32 — Engine Exhaust and Reverser Systems
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What indication does the flight crew receive that the thrust reversers have deployed?
Show the answer and explanation
Answer: A sequence of position-indicating lights
Why: Thrust-reverser deployment is confirmed to the crew by cockpit position indications, typically a sequence of lights showing the reverser unlocking, transiting, and reaching the deployed position. The crew rely on these positive position indications rather than on the physical sensation of deceleration or an audible warning.· FAA-H-8083-32 — Engine Exhaust and Reverser Systems
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The exhaust manifold of a reciprocating engine collects:
Show the answer and explanation
Answer: Exhaust gases from the individual cylinders and routes them to the exhaust pipe
Why: Per FAA-H-8083-32, the exhaust manifold gathers the burnt combustion gases leaving each cylinder's exhaust port and channels them into the exhaust pipe or tailpipe for discharge overboard. It handles hot gases only; coolant and scavenged oil are managed by separate systems.· FAA-H-8083-32 — Engine Exhaust and Reverser Systems

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Related subject areas

The areas that share the most ground with AM.III.L — study them alongside it.

Turbine Engines (AM.III.B)
Reciprocating Engine Induction and Cooling Systems (AM.III.J)
Engine Inspection (AM.III.C)

Frequently asked questions

Why is carbon monoxide a concern with exhaust shroud cabin heat?: Cabin heat is taken from air warmed by flowing over a hot exhaust component inside a shroud. A crack or leaking joint under that shroud sends exhaust gas straight into the air entering the cabin, and carbon monoxide is colorless and odorless, so the occupants get no warning. That is why shroud-area inspection and leak checks are taken seriously.
How does a thrust reverser work?: It redirects the gas stream forward rather than reversing anything mechanically inside the engine, which keeps rotating in its normal direction. A mechanical blockage design drops clamshell or target doors into the exhaust path behind the nozzle so the gas is turned forward. An aerodynamic design closes blocker doors in the fan duct and routes fan air through forward-angled cascade vanes.
Where are EGT thermocouples located on a turbine engine?: Exhaust gas temperature probes sit in the gas path aft of the turbine, spaced around the duct so the indication averages several probes instead of following one hot spot. Engines that display turbine inlet or interstage temperature place their probes further upstream, which is why two similar-looking gauges can be measuring completely different stations.
Which engines are most likely to have exhaust noise suppressors?: Noise output rises steeply with jet velocity, so turbojets and low-bypass engines, whose exhaust leaves at very high velocity, are the ones fitted with suppression hardware. A high-bypass turbofan surrounds its hot core stream with a much slower fan stream that does most of the mixing on its own, greatly reducing the need for a separate suppressor.
What is the exhaust cone for?: Gas leaving the last turbine stage is still swirling. The exhaust cone and its support struts straighten that flow into a solid jet and cut turbulence, and the annular passage between the cone and the outer duct is divergent, so gas velocity drops and static pressure rises slightly before the flow reaches the tail pipe and nozzle.

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