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.