V Speeds

V speeds are standard airspeed values established to ensure safe flight operations of aircraft. These speeds are derived from performance measurements conducted by aircraft manufacturers and are certified by civil aviation authorities during the certification process. The letter “V” originates from the French word “vitesse,” meaning “speed.” Each V speed represents the critical minimum, maximum, or reference speed applicable to a specific flight phase or maneuver.

V speeds were developed to enhance flight safety, standardize pilot decision-making processes, and define the performance limits of aircraft. These speeds define the equilibrium points of aerodynamic forces acting on the aircraft during flight—lift, drag, thrust, and weight. This enables the pilot to know the safe speed ranges within which maneuvers can be performed during any flight phase.

V speeds vary depending on the aircraft type; each manufacturer determines these values through flight testing during the certification process. The results are published in the Pilot Operating Handbook (POH) or Aircraft Flight Manual (AFM). Pilots are required to adhere to the speed values specified in these documents.

Measurement Principles and Indicators

The measurement of V speeds is based on the indicated airspeed (IAS) obtained via the pitot-static system. IAS is measured using sensors sensitive to atmospheric pressure and airflow. The pitot tube, positioned in the direction of the aircraft’s motion, measures total pressure (dynamic plus static pressure), while the static port senses ambient pressure. The difference between these two pressures is calculated as dynamic pressure and transmitted to the airspeed indicator.

V speeds are values directly readable on this indicator without requiring correction factors. This allows pilots to follow standard safety limits regardless of atmospheric conditions.

In general aviation aircraft, airspeed indicators are color-coded as follows:

• White arc: Represents the safe flight range with flaps extended, from the stall speed in landing configuration (V_SO) to the maximum flap-extended speed (V_FE).
• Green arc: Indicates the normal flight range with flaps retracted, from the stall speed (V_S) to the maximum structural cruising speed (V_NO).
• Yellow arc: Denotes the speed range approaching structural limits, which may be used only briefly in smooth air conditions.
• Red line: The absolute limit speed known as “Never Exceed Speed” (V_NE), exceeding which risks structural damage.

These color codes enable pilots to visually identify speed limits during flight and maintain safe operating values.

V Speeds Related to Takeoff Phase

V₁ – Takeoff Decision Speed

V₁ is the critical speed at which the pilot must decide whether to continue or abort the takeoff. It is defined as both the maximum speed at which a takeoff can be safely stopped and the minimum speed at which the takeoff must be continued. The V₁ value varies according to runway length, air density, runway gradient, aircraft weight, and engine performance.

If an engine failure occurs below V₁, the takeoff can be aborted and the aircraft brought to a stop within the remaining runway. However, if V₁ is exceeded, aborting the takeoff would not leave sufficient distance to stop safely before the runway end. Therefore, V₁ is a fundamental reference point in flight safety known as the “decision speed.”

V_LOF – Lift-Off Speed

V_LOF defines the speed at which the aircraft’s wheels lose contact with the runway. This is the point at which lift force equals the aircraft’s weight. In takeoff performance analysis, V_LOF is calculated considering the aircraft’s wing profile, flap configuration, air density, and runway conditions. This speed is also constrained to ensure it does not exceed the maximum tire rotation speed.

V₂ – Takeoff Safety Speed

V₂ is the minimum speed required for the aircraft to continue a safe climb immediately after takeoff in the event of an engine failure. This speed must be greater than the minimum control speed (V_MC). V₂ ensures directional control and climb performance are maintained during a single-engine failure. Falling below V₂ during takeoff may result in loss of aircraft control.

V Speeds Related to Cruise and Maneuvering Phase

V_A – Maneuvering Speed

V_A is the maximum speed at which full control deflections can be applied without exceeding the aircraft’s structural limits. This speed is particularly important for preserving the aircraft structure during turbulent conditions or sharp turning maneuvers. The V_A value increases with aircraft weight, as greater load requires greater lift force.

V_NO – Normal Cruising Speed Limit

V_NO is the maximum cruising speed that must not be exceeded under normal flight conditions. It marks the upper limit of the green arc and may be used only briefly in smooth air. Exceeding V_NO may subject the aircraft to aerodynamic loads that challenge structural limits.

V_NE – Structural Limit Speed

V_NE means “never exceed speed.” Flying above this speed may cause loss of control surface feedback, structural deformation, or aerodynamic failure. Therefore, V_NE is the highest permissible limit established by the aircraft manufacturer.

V Speeds Related to Landing Phase

V_REF – Approach Reference Speed

V_REF is the speed the aircraft must maintain when crossing the runway threshold at a height of 50 feet during landing approach. It is defined as approximately 1.3 times the stall speed in landing configuration. Flying below V_REF may reduce lift and increase the risk of an early stall. This speed is also critical for maintaining control precision during the final phase of flight.

V_FE – Flap Extended Speed Limit

V_FE is the maximum speed that must not be exceeded when flaps are extended. Exceeding this speed may cause excessive loading or structural deformation of the flap mechanism. Since aircraft typically have multiple flap configurations, a separate V_FE value is defined for each configuration.

V_SO – Landing Configuration Stall Speed

V_SO is the minimum speed at which the wings lose lift in landing configuration (with flaps and landing gear extended). This value marks the lower limit of the white arc. V_SO is used as a reference in landing performance calculations and stopping distance planning.

Other Structural and Operational V Speeds

• V_MC: The minimum speed at which the aircraft can be controlled following an engine failure.
• V_LE: The maximum speed at which the aircraft can be flown with the landing gear extended.
• V_LO: The maximum speed at which the landing gear can be extended or retracted.
• V_S: The stall speed in flap-retracted configuration.
• V_X and V_Y: The speeds for best angle of climb (V_X) and best rate of climb (V_Y), respectively.

All these speeds are determined through manufacturer testing and must not be exceeded beyond the limits specified in the flight manuals.

Factors Affecting V Speed Variability

V speeds are not fixed; they vary depending on flight conditions and environmental factors.

These factors include:

• Aircraft takeoff or landing weight
• Air temperature and density
• Runway length, surface type, and gradient
• Flap and slat configuration
• Engine thrust capacity and failure status
• Load factor and turning maneuvers

The V speeds established by the manufacturer are derived from tests conducted under standard atmospheric conditions. Exceeding these values during flight may introduce structural and aerodynamic risks.

V speeds are standard values that define the fundamental parameters of aircraft performance, structural integrity, and flight safety. These speeds enable pilots to make safe decisions throughout all phases of flight, from takeoff to landing. Each V speed establishes operational limits specific to different flight phases. Adherence to these limits is a prerequisite for a safe flight consistent with the aircraft’s certification data.