What is the difference between anti-icing and deicing?

Anti-icing is preventive: the system is on before entering icing and keeps the surface warm or wetted so ice never bonds. Deicing is corrective: ice is allowed to accumulate and the system then breaks the bond so the airstream carries it away. Heated leading edges and continuous fluid flow are anti-ice, pneumatic boots are deice, and some fluid systems can do either depending on how they are operated.

What inflates pneumatic deicing boots?

Air pressure routed to the boots through a distributor or timer valve. On turbine aircraft the source is engine bleed air; on piston aircraft it is the pressure side of an engine-driven air pump, the same pump whose suction side can drive gyro instruments. The valve sequences the boot sections so only part of the leading edge inflates at a time, then vents them and reapplies vacuum to hold them flat.

How does a weeping wing (TKS) ice protection system work?

A glycol-based fluid is pumped to porous panels along the leading edges of the wing and tail, and on some installations the propeller and windshield as well. The fluid seeps through thousands of tiny laser-drilled holes and flows back over the surface, lowering the freezing point of the water film so ice cannot bond. Protection lasts only as long as the fluid supply, so endurance is a planning limit.

How are pitot tubes and static ports protected from ice?

By electric heating elements built into the probe or around the port. The check is to switch pitot heat on and confirm current draw or that the probe warms within seconds, rather than a long ground run that can overheat an unventilated probe. Because a blocked pitot or static system corrupts airspeed and altitude indications, these heaters are verified during routine inspections.

When should pneumatic deicing boots be cycled?

The traditional written-test reasoning is to wait until a measurable layer has built up, on the theory that inflating too early lets thin ice form a shell the boot cannot break. Current guidance for many airplanes is to activate at the first indication of ice accumulation instead. Answer the test question from the handbook reasoning, but on a real aircraft follow the approved flight manual for that model.

On a typical pneumatic deicing system, what causes the inflatable boots on the wing and tail leading edges to expand?

Engine bleed air or pump pressure directed into the boot tubes

Electrical heating elements bonded inside the boot tubes

Hydraulic fluid pumped through the boot tubes

What is the fundamental difference between an anti-icing system and a deicing system?

Anti-icing prevents ice from forming; deicing removes ice after it forms

Anti-icing removes ice after it forms; deicing prevents ice from forming

Anti-icing is used in flight; deicing is used only on the ground

On most turbine-engine aircraft, the primary heat source for thermal anti-icing of the wing leading edges is provided by

hot bleed air ducted from the engine compressor

exhaust gas recirculated through the leading edge

electrical resistance heaters embedded in the skin

In a 'weeping wing' (TKS-type) ice protection system, ice is controlled by

exuding a freezing-point-depressant fluid through a porous panel

circulating heated engine oil through the leading edge

inflating rubber boots along the leading edge surface

A pitot tube and static ports are most commonly protected from ice by

internal electrical heating elements

bleed-air thermal anti-ice ducting

When operating a pneumatic deicing boot system, why should boots generally not be cycled until a measurable amount of ice has accumulated?

Cycling on thin ice can form a shell that the boots bridge rather than break

Early cycling overheats the boots and cracks the rubber surface

Early cycling drains the static system and disables the altimeter

In a pneumatic deicing system, what is the function of the distributor (timer) valve assembly?

It sequences inflation and deflation of the boots in the proper order

It meters anti-ice fluid to the porous leading-edge panels

It regulates the cabin pressurization supplied to the boots

Between deicing cycles, pneumatic boots are typically held flat against the leading edge by

applying engine or pump vacuum (suction) to the boot tubes

spring tension built into the boot fabric

continuous low-pressure air bleeding into the tubes

Windshields on many transport aircraft are protected against ice and fog by

a transparent conductive film that electrically heats the glass laminate

a porous panel that weeps anti-ice fluid across the glass

pneumatic boots bonded to the windshield frame edges

Many pneumatic deicing boots include a conductive (graphite) coating on the outer surface primarily to

dissipate static electricity that would otherwise damage the rubber

generate heat to assist the inflation cycle in melting ice

seal the surface against fluid absorption from the runway

On many transport aircraft, electrical windshield heat for anti-icing and anti-fogging is supplied from a

variable-frequency generator, supplied directly to the windshield element.

variable-frequency generator, supplied through a rectifier to the windshield.

DC generator, supplied through a step-up transformer to the windshield.

Pitot tubes (pitot heads) on transport aircraft are most commonly protected from ice formation

by integral electrical heating elements.

by compressed engine bleed air.

by kinetic (frictional) heating of the airflow.

On a turbine aircraft equipped with a pneumatic (thermal anti-ice) wing leading edge system, what is the source of the heat used to prevent ice formation?

Hot compressor bleed air ducted through the leading edges

Electrical resistance heating elements bonded to the skin

Engine oil pumped through internal leading-edge passages

What is the fundamental difference between an anti-ice system and a de-ice system?

Anti-ice prevents ice from forming; de-ice removes ice after it has formed

Anti-ice removes ice after it forms; de-ice prevents ice from forming

Anti-ice uses electricity; de-ice always uses bleed air

How do pneumatic deicer boots remove ice from a wing leading edge?

They inflate to crack the ice, which is then carried away by the airstream

They spray a freezing-point depressant onto the ice

They heat the leading edge to melt the accumulated ice

When pneumatic deicer boots are not being inflated during normal operation, how are they held tight against the leading edge contour?

Vacuum (suction) is applied to hold the boots deflated

Ram air pressure presses them against the wing

Spring tension in the boot fabric pulls them flat

Which surfaces are most commonly protected by an electrically heated anti-icing element?

Pitot tubes, stall-warning vanes, and windshields

The entire wing upper and lower surfaces

Besides preventing ice, electrically heating a laminated windshield also serves what additional purpose?

It increases the windshield's resistance to bird strikes

It tints the windshield to reduce glare

It removes static electricity from the airframe

An electrically heated propeller de-ice system most commonly uses what component to deliver current to the rotating blades?

A flexible coiled cord between hub and blade

In a thermal anti-ice system that uses engine bleed air, after the air has heated the leading edge it is typically discharged where?

Overboard through exit holes in the lower wing surface

Into the cabin pressurization system

Back into the engine compressor inlet

What is the primary function of a windshield wiper system on an aircraft?

To clear rain from the windshield and maintain pilot visibility

To distribute defog air across the glass

To anti-ice the windshield electrically

A chemical rain-repellent system improves visibility in rain by doing what?

Causing rain to bead up and be blown off the windshield by the airstream

Heating the windshield to evaporate the rain

Increasing the windshield's transparency by dissolving the rain

Why should a chemical rain repellent be applied to the windshield only when there is rain present and the wipers are in use?

On a dry windshield it leaves a film that obscures vision

It will corrode the dry windshield seals

It will freeze instantly on a dry windshield

A pneumatic rain-removal system clears the windshield of rain by what means?

Directing a jet of heated air across the outside of the windshield

Drawing a vacuum behind the windshield

Vibrating the windshield to shake off the water

During an operational check of pneumatic deicer boots, the technician should look for which condition that indicates proper operation?

The boots inflate in proper sequence and then deflate and hold tight

Only the outboard boot inflates and the inboard never moves

The boots remain fully inflated continuously while the system is on

Pneumatic deicer boots are bonded to the leading edges and are subject to deterioration. Which of the following is a recommended practice to prolong boot service life?

Keep the boots clean and apply an approved rubber conditioner

Paint the boots with metallic primer for protection

Coat the boots with engine oil to keep them flexible

In a wing thermal anti-ice system, what device controls the flow of hot bleed air into the leading-edge ducts?

Anti-ice shutoff/control valves

Why is ice accumulation on an aircraft considered hazardous in flight?

It increases drag and weight while reducing lift and disrupting airflow

It improves airflow but overheats the engines

It increases lift and makes the aircraft climb uncontrollably

A pitot tube heater is best classified as which type of system?

An electrically heated anti-ice device

A bleed-air thermal de-ice device

When checking the operation of electrically heated pitot tubes and stall-warning vanes on the ground, why must the test be kept brief?

Without airflow to cool them, the elements can overheat and burn out

The heaters interfere with radio reception when energized

Prolonged operation drains the battery completely

In an engine inlet anti-ice system on a turbine engine, why is it especially important to prevent ice from forming on the inlet lip and guide vanes?

Ingested ice can damage the compressor and disrupt engine airflow

Ice on the inlet shorts out the ignition system

Ice on the inlet adds excessive weight to the nose

A propeller anti-ice system that uses fluid distributes the anti-icing fluid along the blade leading edge primarily by what action?

Centrifugal force slinging the fluid outward along the blades

Bleed-air pressure forcing it along the blade

Gravity feeding it from the blade tip inward

A turbofan engine cowl (nacelle) anti-ice system is most commonly supplied with heat from what source?

Hot compressor bleed air ducted to the cowl lip

Engine oil circulated through the cowl

Electrical heater mats on the outer cowl skin

Which statement best describes why deicer boots should not be left inflated for long periods or operated when there is no ice present?

Continuous inflation disturbs airflow and unnecessarily wears the boots

Inflating the boots increases the wing's lift dangerously

The boots will freeze permanently in the inflated shape

Ice and Rain Control Systems — FAA A&P Test Questions (ACS AM.II.L)

Ice and Rain Control Systems is a small Airframe area that is quick to lock down, because most questions ask only which system does what. The FAA separates anti-icing, which prevents ice from forming, from deicing, which removes ice already there, then asks how each hardware family achieves it: pneumatic boots, thermal bleed air, glycol weeping panels, electric heat for probes and windshields, and rain removal. Get the power source and the operating principle right for each system and this area goes quickly. This page maps it and drills the published questions.

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.II.L covers

The organizing idea is anti-ice versus deice. Anti-icing runs before and during exposure so ice never bonds; deicing lets a measurable layer build and then breaks it off. Pneumatic boots are the classic deice system, inflatable rubber tubes bonded to the wing and tail leading edges that expand to crack accumulated ice, which the airstream then carries away. Inflation air comes from engine bleed air on turbine aircraft, or from the pressure side of an engine-driven air pump on piston aircraft. A distributor or timer valve sequences the boot sections in a set order and controls how long each stays inflated, and between cycles the system holds the boots flat against the leading edge with vacuum so they do not disturb the airfoil. Thermal anti-icing on turbine aircraft uses hot compressor bleed air ducted through piccolo tubes inside the wing and empennage leading edges and the engine inlets, not exhaust heat. Fluid systems, commonly called weeping wings, exude a glycol-based fluid through porous panels to depress the freezing point and stop ice adhering, and they can run as anti-ice or deice depending on flow and timing. Pitot tubes, static ports, stall warning vanes and temperature probes use electric heating elements, so heater checks and their circuit protection are tested. Windshields use electrically heated conductive film, heated air or fluid, while rain is handled by wipers, chemical repellent, pneumatic blast or hydrophobic coatings. Propeller ice control appears here too, with electric blade boots on a timer or alcohol from a slinger ring. FAA-H-8083-31 covers the hardware, and boot inspection, cleaning and leak checks are tested alongside operation.

Where this sits on the test

ACS AM.II.L is tested on the FAA Airframe written test, one of 1,739 ACS-tagged questions in the Airframe 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-8083-31

Three traps candidates fall into

Deice boots get called an anti-icing system. Boots are cyclic and remove ice that has already formed, while anti-icing means keeping a surface clear before ice can bond, which is what heated leading edges and continuously flowing fluid systems do. Exam wording turns on that distinction more often than on any hardware detail.
Boots are assumed to be held flat by airflow or by the rubber springing back. The system applies vacuum to the boots between cycles so they stay tight against the leading edge. Without that suction they can balloon in flight and spoil the airfoil, so a boot standing proud points at lost vacuum, not lost pressure.
Turbine wing anti-ice gets attributed to exhaust heat or to an electric mat. On most turbine aircraft it is hot air bled from the engine compressor and ducted through piccolo tubes in the leading edge. On piston aircraft, boot inflation air comes from the pressure side of the engine-driven air pump instead.

37 free sample questions from ACS AM.II.L

AM.II.LTap an answer
On a typical pneumatic deicing system, what causes the inflatable boots on the wing and tail leading edges to expand?
Show the answer and explanation
Answer: Engine bleed air or pump pressure directed into the boot tubes
Why: Pneumatic deicing boots use rubber tubes that are inflated with regulated pressurized air (from engine bleed air on turbine aircraft or an engine-driven pump on reciprocating aircraft). The inflation flexes the boot, cracking accumulated ice so airflow sheds it. Heating elements are used in anti-icing, not pneumatic boots; hydraulic fluid is not routed into boots.· FAA-H-8083-31 — Ice and Rain Protection, Pneumatic Deicing Boots
AM.II.LTap an answer
What is the fundamental difference between an anti-icing system and a deicing system?
Show the answer and explanation
Answer: Anti-icing prevents ice from forming; deicing removes ice after it forms
Why: Anti-icing systems operate continuously to keep ice from accumulating in the first place (for example, heated leading edges or weeping-wing fluid). Deicing systems allow a small amount of ice to build up and then break or shed it, as with pneumatic boots. The distinction is prevention versus removal, not flight versus ground.· FAA-H-8083-31 — Ice and Rain Protection, Ice Control Systems
AM.II.LTap an answer
On most turbine-engine aircraft, the primary heat source for thermal anti-icing of the wing leading edges is provided by
Show the answer and explanation
Answer: hot bleed air ducted from the engine compressor
Why: Thermal anti-ice systems on transport-category turbine aircraft route hot compressor bleed air through ducting inside the leading edge to keep surfaces above freezing. Electrical heating is typically reserved for smaller surfaces such as probes and windshields. Exhaust gas is not piped to the wing leading edge.· FAA-H-8083-31 — Ice and Rain Protection, Thermal Anti-Icing Systems
AM.II.LTap an answer
In a 'weeping wing' (TKS-type) ice protection system, ice is controlled by
Show the answer and explanation
Answer: exuding a freezing-point-depressant fluid through a porous panel
Why: A weeping wing uses a glycol-based freezing-point-depressant fluid pumped through laser-drilled porous panels (titanium or stainless) on the leading edges. The fluid lowers the freezing point of water and flows back over the surface to prevent ice. It does not use inflatable boots or circulated engine oil.· FAA-H-8083-31 — Ice and Rain Protection, Chemical (Fluid) Anti-Icing Systems
AM.II.LTap an answer
A pitot tube and static ports are most commonly protected from ice by
Show the answer and explanation
Answer: internal electrical heating elements
Why: Pitot tubes, static ports, stall warning vanes, and similar small probes are heated by built-in electrical resistance elements controlled by a switch in the cockpit. Bleed-air ducting and pneumatic boots are used on larger structural surfaces, not on small instrument probes.· FAA-H-8083-31 — Ice and Rain Protection, Electrically Heated Systems
AM.II.LTap an answer
When operating a pneumatic deicing boot system, why should boots generally not be cycled until a measurable amount of ice has accumulated?
Show the answer and explanation
Answer: Cycling on thin ice can form a shell that the boots bridge rather than break
Why: If boots are inflated while only a thin layer of ice is present, the ice can stretch and form a hollow shell over the inflated boot; when the boot deflates the ice remains, and subsequent cycles merely bridge the void. The handbook notes ice should be allowed to build to a recommended thickness before cycling. Boots are not electrically heated, and they are independent of the static system.· FAA-H-8083-31 — Ice and Rain Protection, Deicing Boot Operation (ice bridging)
AM.II.LTap an answer
In a pneumatic deicing system, what is the function of the distributor (timer) valve assembly?
Show the answer and explanation
Answer: It sequences inflation and deflation of the boots in the proper order
Why: The distributor or timer routes pressure to inflate boot sections in a programmed sequence and then connects them to vacuum/suction for deflation so the boots lie flat in normal flight. It does not handle cabin pressurization, and fluid metering belongs to a weeping-wing system, not a pneumatic boot system.· FAA-H-8083-31 — Ice and Rain Protection, Pneumatic System Components
AM.II.LTap an answer
Between deicing cycles, pneumatic boots are typically held flat against the leading edge by
Show the answer and explanation
Answer: applying engine or pump vacuum (suction) to the boot tubes
Why: When boots are not inflating, the system applies suction (vacuum) to the tubes to hold the boots tight against the airfoil, minimizing aerodynamic drag and preventing flutter. Boots rely on applied vacuum, not internal springs or a continuous low-pressure air supply, to stay flat.· FAA-H-8083-31 — Ice and Rain Protection, Deicing Boot Operation
AM.II.LTap an answer
Windshields on many transport aircraft are protected against ice and fog by
Show the answer and explanation
Answer: a transparent conductive film that electrically heats the glass laminate
Why: Electrically heated windshields use a thin transparent conductive coating laminated into the glass; current passing through the film warms the panel, controlled by a temperature sensor and controller. This also improves bird-strike resistance by keeping the laminate warm. Boots and weeping panels are not used on windshields.· FAA-H-8083-31 — Ice and Rain Protection, Windshield Anti-Icing
AM.II.LTap an answer
Many pneumatic deicing boots include a conductive (graphite) coating on the outer surface primarily to
Show the answer and explanation
Answer: dissipate static electricity that would otherwise damage the rubber
Why: The conductive coating bleeds off static electrical charges that build on the boot surface; without it, static discharge can pinhole and deteriorate the rubber. The coating does not produce heat (boots are pneumatic, not heated) and is not a fluid sealant.· FAA-H-8083-31 — Ice and Rain Protection, Deicing Boot Construction and Care
AM.II.LTap an answer
On many transport aircraft, electrical windshield heat for anti-icing and anti-fogging is supplied from a
Show the answer and explanation
Answer: variable-frequency generator, supplied directly to the windshield element.
Why: The resistive conductive film bonded into a heated windshield produces heat regardless of supply frequency, so AC from a variable-frequency (frequency-wild) generator is fed directly to the heating element without a rectifier or transformer. A controller regulates power based on an embedded temperature sensor. (FAA-H-8083-31, Ice and Rain Control Systems — electrically heated windshields.)· FAA-H-8083-31 — Ice and Rain Control Systems
AM.II.LTap an answer
Pitot tubes (pitot heads) on transport aircraft are most commonly protected from ice formation
Show the answer and explanation
Answer: by integral electrical heating elements.
Why: Per FAA-H-8083-31, pitot heads are anti-iced by integral electrical heating elements that keep the ram-air entry clear of ice. Kinetic (frictional) heating is incidental and unreliable, and engine bleed air is not routed to the pitot probe.· FAA-H-8083-31 — Ice and Rain Control Systems
AM.II.LTap an answer
On a turbine aircraft equipped with a pneumatic (thermal anti-ice) wing leading edge system, what is the source of the heat used to prevent ice formation?
Show the answer and explanation
Answer: Hot compressor bleed air ducted through the leading edges
Why: Per FAA-H-8083-31, thermal anti-ice systems on turbine aircraft route hot compressor bleed air through ducts inside the leading edges of the wings and empennage to keep the surfaces warm enough to prevent ice accumulation.· FAA-H-8083-31 — Ice and Rain Control Systems
AM.II.LTap an answer
What is the fundamental difference between an anti-ice system and a de-ice system?
Show the answer and explanation
Answer: Anti-ice prevents ice from forming; de-ice removes ice after it has formed
Why: Per FAA-H-8083-31, anti-icing equipment is turned on before entering icing conditions to prevent ice from forming, whereas de-icing equipment removes ice after it has already accumulated on a surface.· FAA-H-8083-31 — Ice and Rain Control Systems
AM.II.LTap an answer
How do pneumatic deicer boots remove ice from a wing leading edge?
Show the answer and explanation
Answer: They inflate to crack the ice, which is then carried away by the airstream
Why: Per FAA-H-8083-31, pneumatic deicer boots are inflated with air pressure, causing them to expand and crack the accumulated ice; the ice is then carried away by the airstream. When deflated they return to the contour of the leading edge.· FAA-H-8083-31 — Ice and Rain Control Systems
AM.II.LTap an answer
On many reciprocating-engine aircraft, what is the source of operating air pressure for pneumatic deicer boots?
Show the answer and explanation
Answer: An engine-driven air pump
Why: Per FAA-H-8083-31, on reciprocating-engine aircraft the pressure to inflate the deicer boots is supplied by the engine-driven air pump (the pressure side of the vacuum/pneumatic pump system), while the suction side holds the boots deflated against the leading edge.· FAA-H-8083-31 — Ice and Rain Control Systems
AM.II.LTap an answer
When pneumatic deicer boots are not being inflated during normal operation, how are they held tight against the leading edge contour?
Show the answer and explanation
Answer: Vacuum (suction) is applied to hold the boots deflated
Why: Per FAA-H-8083-31, between inflation cycles a vacuum (suction) is applied to the deicer boots to hold them flat and tight against the leading edge so they do not disturb airflow over the wing.· FAA-H-8083-31 — Ice and Rain Control Systems
AM.II.LTap an answer
Which surfaces are most commonly protected by an electrically heated anti-icing element?
Show the answer and explanation
Answer: Pitot tubes, stall-warning vanes, and windshields
Why: Per FAA-H-8083-31, electrical heating is commonly used to anti-ice or de-ice items such as pitot tubes, static ports, stall-warning vanes, windshields, propellers, and small components where running electrical current through a resistance element is practical.· FAA-H-8083-31 — Ice and Rain Control Systems
AM.II.LTap an answer
Besides preventing ice, electrically heating a laminated windshield also serves what additional purpose?
Show the answer and explanation
Answer: It increases the windshield's resistance to bird strikes
Why: Per FAA-H-8083-31, warming a laminated glass/vinyl windshield not only prevents ice and fog but also increases the resiliency of the vinyl interlayer, improving its resistance to bird strikes and cracking when the windshield is at operating temperature.· FAA-H-8083-31 — Ice and Rain Control Systems
AM.II.LTap an answer
An electrically heated propeller de-ice system most commonly uses what component to deliver current to the rotating blades?
Show the answer and explanation
Answer: Brushes riding on slip rings
Why: Per FAA-H-8083-31, electric propeller deicing uses heating elements (boots) bonded to the blade shanks; current is carried from the stationary aircraft electrical system to the rotating spinner/hub assembly through brushes riding on slip rings.· FAA-H-8083-31 — Ice and Rain Control Systems
AM.II.LTap an answer
In a thermal anti-ice system that uses engine bleed air, after the air has heated the leading edge it is typically discharged where?
Show the answer and explanation
Answer: Overboard through exit holes in the lower wing surface
Why: Per FAA-H-8083-31, after the hot bleed air flows through the leading-edge ducts and gives up its heat, it is vented overboard through exit holes or slots on the lower surface of the wing or empennage leading edge.· FAA-H-8083-31 — Ice and Rain Control Systems
AM.II.LTap an answer
What is the primary function of a windshield wiper system on an aircraft?
Show the answer and explanation
Answer: To clear rain from the windshield and maintain pilot visibility
Why: Per FAA-H-8083-31, windshield wipers are a rain-control device that mechanically clears rain and other moisture from the windshield to maintain the pilot's outside visibility, similar to those on an automobile.· FAA-H-8083-31 — Ice and Rain Control Systems
AM.II.LTap an answer
A chemical rain-repellent system improves visibility in rain by doing what?
Show the answer and explanation
Answer: Causing rain to bead up and be blown off the windshield by the airstream
Why: Per FAA-H-8083-31, a chemical rain repellent is sprayed onto the windshield where it changes the surface tension so that rain beads up and is blown away by the airstream rather than spreading into a film, greatly improving visibility.· FAA-H-8083-31 — Ice and Rain Control Systems
AM.II.LTap an answer
Why should a chemical rain repellent be applied to the windshield only when there is rain present and the wipers are in use?
Show the answer and explanation
Answer: On a dry windshield it leaves a film that obscures vision
Why: Per FAA-H-8083-31, rain repellent applied to a dry windshield will leave a film or smear that obscures vision; the repellent is intended to mix with water, so it should be applied only when rain is present so it can spread and be wiped to a clean film.· FAA-H-8083-31 — Ice and Rain Control Systems
AM.II.LTap an answer
A pneumatic rain-removal system clears the windshield of rain by what means?
Show the answer and explanation
Answer: Directing a jet of heated air across the outside of the windshield
Why: Per FAA-H-8083-31, a pneumatic (air-curtain) rain-removal system directs a high-velocity sheet of heated bleed air across the outside of the windshield, which blows the rain off and also warms the glass to evaporate moisture.· FAA-H-8083-31 — Ice and Rain Control Systems
AM.II.LTap an answer
During an operational check of pneumatic deicer boots, the technician should look for which condition that indicates proper operation?
Show the answer and explanation
Answer: The boots inflate in proper sequence and then deflate and hold tight
Why: Per FAA-H-8083-31, an operational check of deicer boots should show the boots inflating in the proper sequence and then deflating, with the boots holding vacuum tight against the leading edge between cycles. Symmetrical, sequential inflation/deflation indicates correct operation.· FAA-H-8083-31 — Ice and Rain Control Systems
AM.II.LTap an answer
Pneumatic deicer boots are bonded to the leading edges and are subject to deterioration. Which of the following is a recommended practice to prolong boot service life?
Show the answer and explanation
Answer: Keep the boots clean and apply an approved rubber conditioner
Why: Per FAA-H-8083-31, rubber deicer boots are protected and their life extended by keeping them clean and applying a manufacturer-approved conditioner/protectant; petroleum products, oil, grease, and dirt deteriorate the rubber and must be removed.· FAA-H-8083-31 — Ice and Rain Control Systems
AM.II.LTap an answer
In a wing thermal anti-ice system, what device controls the flow of hot bleed air into the leading-edge ducts?
Show the answer and explanation
Answer: Anti-ice shutoff/control valves
Why: Per FAA-H-8083-31, the flow of bleed air to the wing and empennage thermal anti-ice ducts is controlled by anti-ice shutoff/control valves, which open when anti-ice is selected and regulate the supply of hot air to the surfaces.· FAA-H-8083-31 — Ice and Rain Control Systems
AM.II.LTap an answer
Why is ice accumulation on an aircraft considered hazardous in flight?
Show the answer and explanation
Answer: It increases drag and weight while reducing lift and disrupting airflow
Why: Per FAA-H-8083-31, ice disrupts the smooth airflow over the wings and tail, increasing drag and weight while reducing lift; it can also restrict control surface movement and clog inlets and sensors, all of which degrade aircraft performance and safety.· FAA-H-8083-31 — Ice and Rain Control Systems
AM.II.LTap an answer
A pitot tube heater is best classified as which type of system?
Show the answer and explanation
Answer: An electrically heated anti-ice device
Why: Per FAA-H-8083-31, the pitot tube contains an internal electric heating element that is energized to keep the tube warm, preventing ice from forming and blocking the ram-air opening; it is an electrically heated anti-ice device.· FAA-H-8083-31 — Ice and Rain Control Systems
AM.II.LTap an answer
When checking the operation of electrically heated pitot tubes and stall-warning vanes on the ground, why must the test be kept brief?
Show the answer and explanation
Answer: Without airflow to cool them, the elements can overheat and burn out
Why: Per FAA-H-8083-31, these heated elements rely on the cooling effect of airflow in flight; on the ground there is no cooling airflow, so prolonged energizing can overheat and burn out the heating elements or cause injury, so checks are kept short and the units are not touched.· FAA-H-8083-31 — Ice and Rain Control Systems
AM.II.LTap an answer
In an engine inlet anti-ice system on a turbine engine, why is it especially important to prevent ice from forming on the inlet lip and guide vanes?
Show the answer and explanation
Answer: Ingested ice can damage the compressor and disrupt engine airflow
Why: Per FAA-H-8083-31, ice forming on the engine inlet can break loose and be ingested into the compressor, causing foreign object damage and possible engine failure; ice also disrupts inlet airflow and reduces engine performance, so the inlet is anti-iced with bleed air.· FAA-H-8083-31 — Ice and Rain Control Systems
AM.II.LTap an answer
A propeller anti-ice system that uses fluid distributes the anti-icing fluid along the blade leading edge primarily by what action?
Show the answer and explanation
Answer: Centrifugal force slinging the fluid outward along the blades
Why: Per FAA-H-8083-31, in a fluid propeller anti-ice system the fluid is fed to a slinger ring on the hub; centrifugal force then throws (slings) the fluid outward along the blades, where feed shoes guide it down the leading edge to prevent ice from forming.· FAA-H-8083-31 — Ice and Rain Control Systems
AM.II.LTap an answer
What component in a fluid propeller deice/anti-ice system feeds anti-ice fluid from the hub onto the rotating blades?
Show the answer and explanation
Answer: A slinger ring
Why: Per FAA-H-8083-31, a slinger ring mounted on the propeller hub receives fluid from a stationary nozzle and, using centrifugal force, distributes it to feed shoes on each blade, which carry the fluid along the leading edge.· FAA-H-8083-31 — Ice and Rain Control Systems
AM.II.LTap an answer
A turbofan engine cowl (nacelle) anti-ice system is most commonly supplied with heat from what source?
Show the answer and explanation
Answer: Hot compressor bleed air ducted to the cowl lip
Why: Per FAA-H-8083-31, engine cowl/nacelle anti-icing on turbine engines is typically accomplished by ducting hot compressor bleed air into the inlet cowl lip to keep it warm and prevent ice from forming and being ingested.· FAA-H-8083-31 — Ice and Rain Control Systems
AM.II.LTap an answer
A static port and stall-warning sensor are commonly protected from ice by which type of system?
Show the answer and explanation
Answer: Electrical heating elements
Why: Per FAA-H-8083-31, small probes and sensors such as static ports, stall-warning vanes, angle-of-attack sensors, and pitot tubes are protected by internal electrical heating elements that prevent ice from forming and blocking or jamming them.· FAA-H-8083-31 — Ice and Rain Control Systems
AM.II.LTap an answer
Which statement best describes why deicer boots should not be left inflated for long periods or operated when there is no ice present?
Show the answer and explanation
Answer: Continuous inflation disturbs airflow and unnecessarily wears the boots
Why: Per FAA-H-8083-31, deicer boots are designed to cycle to break ice; leaving them inflated or cycling them with no ice (especially with thin ice present) can be ineffective and unnecessarily wears the boots, while continuous inflation disturbs airflow and degrades wing performance. The boots are inflated only to crack accumulated ice, then deflated.· FAA-H-8083-31 — Ice and Rain Control Systems

Failed AM.II.L on your AKTR?

Enter the ACS codes from your FAA fail report and get a targeted study plan — the exact areas the examiner must re-test you on, with the handbook references for each.

Build my remediation plan

Related subject areas

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

Environmental Systems (AM.II.G)
Hydraulic and Pneumatic Systems (AM.II.F)
Turbine Engine Air Systems (AM.III.K)

Frequently asked questions

What is the difference between anti-icing and deicing?: Anti-icing is preventive: the system is on before entering icing and keeps the surface warm or wetted so ice never bonds. Deicing is corrective: ice is allowed to accumulate and the system then breaks the bond so the airstream carries it away. Heated leading edges and continuous fluid flow are anti-ice, pneumatic boots are deice, and some fluid systems can do either depending on how they are operated.
What inflates pneumatic deicing boots?: Air pressure routed to the boots through a distributor or timer valve. On turbine aircraft the source is engine bleed air; on piston aircraft it is the pressure side of an engine-driven air pump, the same pump whose suction side can drive gyro instruments. The valve sequences the boot sections so only part of the leading edge inflates at a time, then vents them and reapplies vacuum to hold them flat.
How does a weeping wing (TKS) ice protection system work?: A glycol-based fluid is pumped to porous panels along the leading edges of the wing and tail, and on some installations the propeller and windshield as well. The fluid seeps through thousands of tiny laser-drilled holes and flows back over the surface, lowering the freezing point of the water film so ice cannot bond. Protection lasts only as long as the fluid supply, so endurance is a planning limit.
How are pitot tubes and static ports protected from ice?: By electric heating elements built into the probe or around the port. The check is to switch pitot heat on and confirm current draw or that the probe warms within seconds, rather than a long ground run that can overheat an unventilated probe. Because a blocked pitot or static system corrupts airspeed and altitude indications, these heaters are verified during routine inspections.
When should pneumatic deicing boots be cycled?: The traditional written-test reasoning is to wait until a measurable layer has built up, on the theory that inflating too early lets thin ice form a shell the boot cannot break. Current guidance for many airplanes is to activate at the first indication of ice accumulation instead. Answer the test question from the handbook reasoning, but on a real aircraft follow the approved flight manual for that model.

All 40 ACS areas

General

Airframe

Powerplant

Primary sources

Drill ACS AM.II.L inside the full Airframe bank

Adaptive engine, timed exam simulator, ACS-code remediation, and oral prep — everything you need to pass.

Start free See plans