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Wiper performance in heavy rain

Aviation Mechanic Airframe (AMA) practice question 2 of 9 on Ice and Rain Control Systems. ACS element AM.II.L.K7 · difficulty: recall. Want to answer it in a timed quiz? Use the Aviation Mechanic Airframe (AMA) practice mode.

Question bank updated 2026-09-22

QUESTIONMost windshield wiper systems fail to provide satisfactory vision in heavy rain. One of the two basic problem areas is that slipstream aerodynamic forces tend to

  1. Araise blade pressure on the window
  2. Bfreeze the blade to the windshield glass
  3. Creduce blade pressure on the window
Show the answer and explanation

Correct answer: C. reduce blade pressure on the window

  • A — incorrect The airflow lifts the blade rather than pressing it down, which is why wiping becomes ineffective at speed.
  • B — incorrect Freezing of the blade is not one of the two stated wiper problem areas; the issues are reduced blade loading and insufficient oscillation speed.
  • C — correct Slipstream aerodynamic forces reduce the wiper blade loading pressure on the window, which causes ineffective wiping or streaking.

BACKGROUND

Rain, and the frost, fog, and ice that form on flight deck windows, all degrade the crew's vision and drive the design of rain control and window heat systems. Windshield wipers have two basic problem areas. The first is the tendency of slipstream aerodynamic forces to reduce the wiper blade loading pressure on the window, causing ineffective wiping or streaking. The second is achieving wiper oscillation fast enough to keep up with high rain impingement rates during heavy rainfall. Because of these limits, other methods are used, including pneumatic rain removal that directs heated air over the windshield to break up the drops and keep moisture from freezing, and hydrophobic surface seal coatings that make raindrops bead up and roll off with very little distortion.

STUDY TIP

Memorize the two wiper limitations together with the alternatives that exist because of them: jet blast rain removal, chemical repellent, and hydrophobic coatings.

KEY POINTS

  • Slipstream forces lift the wiper blade, reducing loading pressure and causing streaking.
  • Wiper oscillation may also be too slow for heavy rain impingement rates.
  • Heated-air rain removal and hydrophobic coatings supplement or replace wipers.

SOURCES

  • sources/ama-airframe/ch15.txt — "Pneumatic Rain Removal Systems"
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.