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PilotSchool Knowledge Base

Understanding Airspeed Indicator Markings

Introduction

The Airspeed Indicator (ASI) is an essential flight instrument that provides pilots with the aircraft’s forward speed in relation to the surrounding air. It is part of the larger pitot-static system, which measures air pressure differences to calculate speed. Understanding the ASI’s color-coded markings is crucial for maintaining safe airspeed limits across different phases of flight. This section will cover the various color codes used on ASIs, explain their significance, and describe the associated speeds.

Overview of Color-Coded Markings

The ASI uses a series of color codes to convey vital information about the safe operating limits of an aircraft. These markings help pilots quickly assess whether they are flying within acceptable speed ranges.

White Arc – Flap Operating Range

  • Lower Limit (VSO): Represents the stalling speed or minimum steady flight speed in the landing configuration (flaps and landing gear down).
  • Upper Limit (VFE): Denotes the maximum speed at which the aircraft can safely fly with the flaps extended.
  • Significance: This range is crucial for safe approaches and landings, where the use of flaps is necessary to control descent and approach angles.

Green Arc – Normal Operating Range

  • Lower Limit (VS1): Indicates the stalling speed or minimum steady flight speed in a particular configuration, typically with gear and flaps retracted.
  • Upper Limit (VNO): Marks the maximum structural cruising speed, which should only be approached in smooth air conditions.
  • Significance: The green arc covers most operational speeds under typical flight conditions, ensuring the aircraft remains within safe performance limits.

Yellow Arc – Caution Range

  • Significance: Denotes speeds that should be flown with caution and only in smooth air conditions. Flying in this range in turbulent air could cause structural stress or damage.

Red Radial Line – Never Exceed Speed

  • Speed (VNE): This is the maximum airspeed that must never be exceeded to prevent structural failure.
  • Significance: Exceeding this speed poses severe risks to aircraft integrity and structural safety, potentially leading to catastrophic failures.

Additional Airspeed Limitations (Not Marked on ASI)

  • VA: The design maneuvering speed above which full or abrupt control deflections should not be made.
  • VLO: Maximum landing gear operating speed.
  • VLE: Maximum speed with the landing gear extended.
  • VX: Best angle-of-climb speed.
  • VY: Best rate-of-climb speed.
  • VYSE: Best rate-of-climb speed with one engine inoperative, specific to multi-engine aircraft.
  • VMC: Minimum control speed with one engine inoperative in multi-engine aircraft.

Importance

Color-coded markings on the ASI are vital for quick visual reference, allowing pilots to maintain speeds that are safe for the aircraft’s current configuration and environmental conditions. Abiding by these color-coded ranges ensures structural integrity and operational safety during all phases of flight.

Sources

Understanding the ASI and its markings is indispensable for pilots to operate their aircraft within safe parameters, reducing risks associated with exceeding structural limits or misjudging aircraft capabilities.