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Wing anti-ice valve failed closed

Aviation Mechanic Airframe (AMA) practice question 7 of 9 on Ice and Rain Control Systems. ACS element AM.II.L.K3 · difficulty: standard. Want to answer it in a timed quiz? Use the Aviation Mechanic Airframe (AMA) practice mode.

Question bank updated 2026-09-22

QUESTIONOn a transport category airplane, one wing anti-ice (WAI) valve fails in the closed position. How does the WAI control card respond?

  1. AIt commands the other valve fully open
  2. BIt sets the other valve to regulate
  3. CIt keeps the other valve closed
Show the answer and explanation

Correct answer: C. It keeps the other valve closed

  • A — incorrect Opening the opposite valve would heat only one wing and upset the airplane's aerodynamic symmetry in icing conditions.
  • B — incorrect Regulating the opposite valve would still leave one wing heated and one unheated, which the control logic is written to prevent.
  • C — correct If either valve fails closed, the WAI control card keeps the opposite valve closed so that the wings are not heated unequally.

BACKGROUND

The wing anti-ice system on a modern transport airplane is controlled by the airfoil and cowl ice protection system (ACIPS) computer card, which operates both WAI valves. The required valve positions change as bleed air temperature and altitude change. The left and right valves operate at the same time so that both wings are heated equally, which keeps the airplane aerodynamically stable in icing conditions. WAI pressure sensors downstream of the valves supply feedback for valve control and position indication; if either pressure sensor fails, the control card drives the related valve either fully open or fully closed. If either valve fails closed, the card keeps the other valve closed as well.

STUDY TIP

Tie the failure logic back to its purpose: symmetric heating. Any answer that leaves one wing heated and the other cold contradicts the design intent.

KEY POINTS

  • The ACIPS computer card controls both WAI valves together.
  • Equal heating of both wings keeps the airplane aerodynamically stable.
  • A valve that fails closed causes the control card to close the opposite valve too.

SOURCES

  • sources/ama-airframe/ch15.txt — "WAI Control System"
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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.