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Removing rain repellent residue from a windshield

Aviation Mechanic Airframe (AMA) practice question 4 of 9 on Ice and Rain Control Systems. ACS element AM.II.L.R2 · difficulty: standard. Want to answer it in a timed quiz? Use the Aviation Mechanic Airframe (AMA) practice mode.

Question bank updated 2026-09-22

QUESTIONRain repellent has been applied inadvertently to a dry windshield. How should the concentrated repellent and its residue be removed?

  1. ABy running the wipers on high speed
  2. BWith a thorough fresh water rinse
  3. CWith a naphtha-soaked cloth
Show the answer and explanation

Correct answer: B. With a thorough fresh water rinse

  • A — incorrect Operating the wipers or the rain clearing system after an inadvertent application tends to increase smearing rather than clean the window.
  • B — correct Concentrated repellent or residue should be removed by a thorough fresh water rinse at the earliest opportunity to prevent staining or minor corrosion of the aircraft skin.
  • C — incorrect Naphtha is called out for removing grease and oil from rubber deicer boots, not for cleaning repellent from a windshield.

BACKGROUND

Heated transport category windshields are laminated assemblies of glass or polycarbonate plies with conductive coatings or resistance wires built in, so cleaning agents and procedures used on them must be chosen carefully. Rain repellent residue left from application in dry weather or very light rain can cause staining or minor corrosion of the aircraft skin, and any concentrated repellent or residue should be removed by a thorough fresh water rinse at the earliest opportunity. If the repellent is applied inadvertently, the windshield wipers and rain clearing system should not be operated, because that increases smearing. Related handling rules apply to ground deicing: deicing and anti-icing fluids must not be directed onto flight deck or cabin windows, since that can craze acrylics or penetrate window seals, and if Type II, III, or IV fluids are used, all traces must be removed from flight deck windows before departure.

STUDY TIP

Group the window cleaning rules together: fresh water for repellent residue, no wipers after an inadvertent application, and no deicing fluid sprayed onto flight deck windows.

KEY POINTS

  • Fresh water rinse removes concentrated rain repellent and its residue.
  • Running the wipers after an inadvertent application only spreads smearing.
  • Deicing fluid on flight deck windows can craze acrylics and attack window seals.

SOURCES

  • sources/ama-airframe/ch15.txt — "Chemical Rain Repellent"
  • sources/ama-airframe/ch15.txt — "Critical Surfaces"
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MORE ON ICE AND RAIN CONTROL SYSTEMS

SkyDrill is not affiliated with the FAA. This is an original practice item based on FAA-H-8083-31B Aviation Maintenance Technician Handbook – Airframe, and 14 CFR part 43. Regulations and handbooks are revised; confirm details against the current edition.