SkyDrill

When to use chemical rain repellent

Aviation Mechanic Airframe (AMA) practice question 9 of 9 on Ice and Rain Control Systems. ACS element AM.II.L.K5 · difficulty: recall. Want to answer it in a timed quiz? Use the Aviation Mechanic Airframe (AMA) practice mode.

Question bank updated 2026-09-22

QUESTIONUnder what condition should an aircraft chemical rain repellent system be operated?

  1. AAny time the windshield is dry
  2. BOnly in very wet conditions
  3. CWhenever the wipers are parked
Show the answer and explanation

Correct answer: B. Only in very wet conditions

  • A — incorrect Heavy undiluted repellent on a dry window restricts visibility, so the system must not be used on dry glass.
  • B — correct The system is intended for very wet conditions, where the slipstream removes the beaded water and leaves much of the window dry.
  • C — incorrect Wiper position is not the criterion; the amount of water on the windshield is what determines proper use.

BACKGROUND

A rain repellent system applies a chemical onto the outside of the windshield when the crew presses a switch or button, and the proper amount is applied regardless of how long the switch is held; on some systems a solenoid valve controlled by a time delay module meters the repellent to a spray nozzle. The chemical forms a transparent film that makes water draw up into beads, and the high-velocity slipstream carries the beads away, leaving much of the window dry. The system should only be used in very wet conditions, because heavy undiluted repellent restricts window visibility on a dry window. If the system is operated inadvertently, the wipers or rain clearing system should not be run, as that tends to increase smearing. The repellent film deteriorates slowly with continuing rain impingement, so periodic reapplication is necessary.

STUDY TIP

Remember the rule as a pair: apply only in heavy rain, and never chase an accidental application with the wipers.

KEY POINTS

  • Rain repellent beads the water so the slipstream can carry it off the glass.
  • Use only in very wet conditions; undiluted repellent on dry glass restricts vision.
  • The film wears away with continued rain, so reapplication is periodic.

SOURCES

  • sources/ama-airframe/ch15.txt — "Chemical Rain Repellent"
Practice the Aviation Mechanic Airframe (AMA) test →Timed 100-question exam, by ACS area, or review your misses. Free.
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.