On a typical pneumatic deicing system, what causes the inflatable boots on the wing and tail leading edges to expand?
ACS code: AM.II.L
Correct answer: Engine bleed air or pump pressure directed into the boot tubes
Rationale: 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.
What is the fundamental difference between an anti-icing system and a deicing system?
ACS code: AM.II.L
Correct answer: Anti-icing prevents ice from forming; deicing removes ice after it forms
Rationale: 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.
On most turbine-engine aircraft, the primary heat source for thermal anti-icing of the wing leading edges is provided by
ACS code: AM.II.L
Correct answer: hot bleed air ducted from the engine compressor
Rationale: 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.
In a 'weeping wing' (TKS-type) ice protection system, ice is controlled by
ACS code: AM.II.L
Correct answer: exuding a freezing-point-depressant fluid through a porous panel
Rationale: 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.
A pitot tube and static ports are most commonly protected from ice by
ACS code: AM.II.L
Correct answer: internal electrical heating elements
Rationale: 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.
When operating a pneumatic deicing boot system, why should boots generally not be cycled until a measurable amount of ice has accumulated?
ACS code: AM.II.L
Correct answer: Cycling on thin ice can form a shell that the boots bridge rather than break
Rationale: 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.
In a pneumatic deicing system, what is the function of the distributor (timer) valve assembly?
ACS code: AM.II.L
Correct answer: It sequences inflation and deflation of the boots in the proper order
Rationale: 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.
Between deicing cycles, pneumatic boots are typically held flat against the leading edge by
ACS code: AM.II.L
Correct answer: applying engine or pump vacuum (suction) to the boot tubes
Rationale: 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.
Windshields on many transport aircraft are protected against ice and fog by
ACS code: AM.II.L
Correct answer: a transparent conductive film that electrically heats the glass laminate
Rationale: 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.
Many pneumatic deicing boots include a conductive (graphite) coating on the outer surface primarily to
ACS code: AM.II.L
Correct answer: dissipate static electricity that would otherwise damage the rubber
Rationale: 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.
On many transport aircraft, electrical windshield heat for anti-icing and anti-fogging is supplied from a
ACS code: AM.II.L
Correct answer: variable-frequency generator, supplied directly to the windshield element.
Rationale: 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.)
Pitot tubes (pitot heads) on transport aircraft are most commonly protected from ice formation
ACS code: AM.II.L
Correct answer: by integral electrical heating elements.
Rationale: 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.
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?
ACS code: AM.II.L
Correct answer: Hot compressor bleed air ducted through the leading edges
Rationale: 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.
What is the fundamental difference between an anti-ice system and a de-ice system?
ACS code: AM.II.L
Correct answer: Anti-ice prevents ice from forming; de-ice removes ice after it has formed
Rationale: 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.
How do pneumatic deicer boots remove ice from a wing leading edge?
ACS code: AM.II.L
Correct answer: They inflate to crack the ice, which is then carried away by the airstream
Rationale: 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.
On many reciprocating-engine aircraft, what is the source of operating air pressure for pneumatic deicer boots?
ACS code: AM.II.L
Correct answer: An engine-driven air pump
Rationale: 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.
When pneumatic deicer boots are not being inflated during normal operation, how are they held tight against the leading edge contour?
ACS code: AM.II.L
Correct answer: Vacuum (suction) is applied to hold the boots deflated
Rationale: 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.
Which surfaces are most commonly protected by an electrically heated anti-icing element?
ACS code: AM.II.L
Correct answer: Pitot tubes, stall-warning vanes, and windshields
Rationale: 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.
Besides preventing ice, electrically heating a laminated windshield also serves what additional purpose?
ACS code: AM.II.L
Correct answer: It increases the windshield's resistance to bird strikes
Rationale: 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.
An electrically heated propeller de-ice system most commonly uses what component to deliver current to the rotating blades?
ACS code: AM.II.L
Correct answer: Brushes riding on slip rings
Rationale: 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.
In a thermal anti-ice system that uses engine bleed air, after the air has heated the leading edge it is typically discharged where?
ACS code: AM.II.L
Correct answer: Overboard through exit holes in the lower wing surface
Rationale: 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.
What is the primary function of a windshield wiper system on an aircraft?
ACS code: AM.II.L
Correct answer: To clear rain from the windshield and maintain pilot visibility
Rationale: 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.
A chemical rain-repellent system improves visibility in rain by doing what?
ACS code: AM.II.L
Correct answer: Causing rain to bead up and be blown off the windshield by the airstream
Rationale: 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.
Why should a chemical rain repellent be applied to the windshield only when there is rain present and the wipers are in use?
ACS code: AM.II.L
Correct answer: On a dry windshield it leaves a film that obscures vision
Rationale: 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.
A pneumatic rain-removal system clears the windshield of rain by what means?
ACS code: AM.II.L
Correct answer: Directing a jet of heated air across the outside of the windshield
Rationale: 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.
During an operational check of pneumatic deicer boots, the technician should look for which condition that indicates proper operation?
ACS code: AM.II.L
Correct answer: The boots inflate in proper sequence and then deflate and hold tight
Rationale: 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.
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?
ACS code: AM.II.L
Correct answer: Keep the boots clean and apply an approved rubber conditioner
Rationale: 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.
In a wing thermal anti-ice system, what device controls the flow of hot bleed air into the leading-edge ducts?
ACS code: AM.II.L
Correct answer: Anti-ice shutoff/control valves
Rationale: 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.
Why is ice accumulation on an aircraft considered hazardous in flight?
ACS code: AM.II.L
Correct answer: It increases drag and weight while reducing lift and disrupting airflow
Rationale: 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.
A pitot tube heater is best classified as which type of system?
ACS code: AM.II.L
Correct answer: An electrically heated anti-ice device
Rationale: 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.
When checking the operation of electrically heated pitot tubes and stall-warning vanes on the ground, why must the test be kept brief?
ACS code: AM.II.L
Correct answer: Without airflow to cool them, the elements can overheat and burn out
Rationale: 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.
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?
ACS code: AM.II.L
Correct answer: Ingested ice can damage the compressor and disrupt engine airflow
Rationale: 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.
A propeller anti-ice system that uses fluid distributes the anti-icing fluid along the blade leading edge primarily by what action?
ACS code: AM.II.L
Correct answer: Centrifugal force slinging the fluid outward along the blades
Rationale: 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.
What component in a fluid propeller deice/anti-ice system feeds anti-ice fluid from the hub onto the rotating blades?
ACS code: AM.II.L
Correct answer: A slinger ring
Rationale: 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.
A turbofan engine cowl (nacelle) anti-ice system is most commonly supplied with heat from what source?
ACS code: AM.II.L
Correct answer: Hot compressor bleed air ducted to the cowl lip
Rationale: 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.
A static port and stall-warning sensor are commonly protected from ice by which type of system?
ACS code: AM.II.L
Correct answer: Electrical heating elements
Rationale: 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.
Which statement best describes why deicer boots should not be left inflated for long periods or operated when there is no ice present?
ACS code: AM.II.L
Correct answer: Continuous inflation disturbs airflow and unnecessarily wears the boots
Rationale: 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.