# Overspeed Warning System: VMO/MMO Limits, Barber Pole, and Aural Alerts

> Learn overspeed warning logic, PFD barber-pole interpretation, VMO/MMO and configuration limits, plus immediate crew alerting behavior.

- **Subject:** 022 — Instrumentation
- **Section:** 022-12 — Alerting Systems, Proximity Systems
- **Topic code:** 022-12-05
- **Last reviewed:** 2026-03-27
- **Author:** Pablo Asensio Martínez
- **HTML version:** https://pilotsyllabus.com/en/instrumentation/alerting-systems-proximity-systems/overspeed-warning/

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## Overview

The **Overspeed Warning System** is a mandatory safety feature designed to alert the flight crew when the aircraft exceeds its maximum operating speeds ($V_{MO}$ / $M_{MO}$). Its primary purpose is to prevent inadvertent excursions beyond the certified structural limits of the airframe.

## Indications

### Visual (PFD Speed Tape)
On modern Primary Flight Displays (PFD):
*   **Speed Tape:** A vertical moving scale (White on Grey).
*   **Maximum Speed Strip ($V_{MAX}$):** A **Red and Black striped bar** (often called the "Barber Pole") descends from the top of the scale to indicate the upper speed limit.
*   **$V_{MAX}$ Definition:** The strip starts at the **lowest** limiting speed for the current configuration:
    1.  **$V_{MO}$ / $M_{MO}$:** Maximum Operating Speed / Mach.
    2.  **$V_{LE}$:** Maximum Landing Gear Extended Speed.
    3.  **$V_{FE}$:** Maximum Flaps Extended Speed.

### Aural
*   **Alert:** A distinctive, continuous sound (e.g., "Clacker", Siren, or Voice Warning) triggers immediately upon exceeding the limit.

## System Logic
The Warning System monitors Air Data Computer (ADC) inputs. If Indicated Airspeed (IAS) or Mach Number exceeds the calculated limit, the Master Warning (Level A) is triggered.

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