Overspeed Warning System: VMO/MMO Limits, Barber Pole, and Aural Alerts
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:
- $V_{MO}$ / $M_{MO}$: Maximum Operating Speed / Mach.
- $V_{LE}$: Maximum Landing Gear Extended Speed.
- $V_{FE}$: 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.