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

> Understand AoA measurement methods, anti-icing, output paths to ADC and stall-warning systems, and operational implications of sensor failures.

- **Subject:** 022 — Instrumentation
- **Section:** 022-02 — Measurement of Air Data Parameters
- **Topic code:** 022-02-03
- **Last reviewed:** 2026-04-01
- **Author:** Pablo Asensio Martínez
- **HTML version:** https://pilotsyllabus.com/en/instrumentation/measurement-of-air-data-parameters/angle-of-attack-aoa-measurement/

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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)

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Free study notes from pilotsyllabus.com. Not a substitute for training at an approved ATO.