Angle-of-Attack (AoA) Measurement: Sensors, Heating, and Failure Modes

022-02-03Pablo Asensio Martínez2026-04-011 min

The Angle of Attack (AoA) or alpha ($\alpha$) is the angle between the wing's chord line and the relative airflow. It is a critical parameter for stall warning and flight envelope protection.

AoA Sensors

There are two primary types of sensors used to measure AoA:

  1. Vane Detector: An external vane (like a wind vane) that aligns itself with the relative airflow. Potentiometers measure its angle relative to the fuselage.
  2. Slotted Probe (Conical): A probe with two slots (upper and lower). Differential pressure between the slots causes internal paddles to rotate the probe until pressures equalize, aligning it with the airflow.

Anti-Icing: AoA probes are generally electrically heated to prevent ice formation which could freeze the vane/probe in a fixed position.

Failure Modes

If an AoA sensor becomes frozen/stuck:

  • It will fail to detect changes in AoA.
  • The Stall Warning System may fail to activate even if the aircraft approaches a stall.
  • Flight Envelope protections based on alpha limits will be lost.

System Outputs

AoA data is sent to the:

  • Air Data Computer (ADC)
  • Stall Warning System (Stick shaker/pusher)
  • Flight Envelope Protection System (e.g., Alpha Floor protection)
  • AoA Indicator (if fitted)