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Leading edge stall warning switch operation

Aviation Mechanic Airframe (AMA) practice question 17 of 20 on Aircraft Instrument Systems. ACS element AM.II.H.K20 · 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 stall warning system that uses a lightly sprung tab in the wing leading edge, what pushes the tab upward to close the warning circuit as the angle of attack increases?

  1. AAir that diverges downward under the wing.
  2. BAir that diverges upward over the wing.
  3. CSuction created inside the wing cavity.
Show the answer and explanation

Correct answer: B. Air that diverges upward over the wing.

  • A — incorrect Air flowing under the wing is what holds the tab down at normal angle of attack, keeping the switch open.
  • B — correct As the angle of attack increases the point of stagnation moves down, so divergent air flowing up and over the wing pushes the tab upward and closes the switch.
  • C — incorrect Suction drawing air out of a cavity describes the reed-type stall warning device, which sounds a tone rather than operating a switch.

BACKGROUND

Angle of attack, or AOA, awareness ranges from simple stall warning devices to full indicating systems. The simplest device is a reed placed in a cavity just aft of the leading edge with an open passage to a precise point on the leading edge; as the AOA increases, low-pressure air over the curved leading edge sucks air out through the passage and vibrates the reed audibly. Another common device uses an electric switch operated by a small lightly sprung tab near the point of stagnation. At normal AOA the tab is held down by air that diverges at the point of stagnation and flows under the wing, so the switch stays open. As AOA increases, the point of stagnation moves down and the divergent air that flows up and over the wing pushes the tab upward, closing the circuit to a horn or warning light. A true AOA indicating system instead uses an alpha vane or slotted probe on the forward fuselage feeding the air data computer, and many such systems drive a stick shaker to warn of an impending stall.

STUDY TIP

Anchor everything to the point of stagnation: it moves down as angle of attack rises, and that movement is what triggers both the reed and the tab switch.

KEY POINTS

  • The point of stagnation moves down the leading edge as angle of attack increases.
  • Air diverging upward then pushes the sprung tab up and closes the warning circuit.
  • Reed-type devices instead use suction through a leading edge passage to make an audible tone.

SOURCES

  • sources/ama-airframe/ch10.txt "Stall Warning & Angle of Attack (AOA) Indicators" (reed-type and switch-type stall warning devices)
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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.