In aviation

Aviation

Aviation is the design, development, production, operation, and use of aircraft, especially heavier-than-air aircraft. Aviation is derived from avis, the Latin word for bird.-History:...

, V-speeds are standard terms used to define airspeed

Airspeed

Airspeed is the speed of an aircraft relative to the air. Among the common conventions for qualifying airspeed are: indicated airspeed , calibrated airspeed , true airspeed , equivalent airspeed and density airspeed....

s important or useful to the operation of all aircraft

Aircraft

An aircraft is a vehicle that is able to fly by gaining support from the air, or, in general, the atmosphere of a planet. An aircraft counters the force of gravity by using either static lift or by using the dynamic lift of an airfoil, or in a few cases the downward thrust from jet engines.Although...

 including fixed-wing aircraft

Fixed-wing aircraft

A fixed-wing aircraft is an aircraft capable of flight using wings that generate lift due to the vehicle's forward airspeed. Fixed-wing aircraft are distinct from rotary-wing aircraft in which wings rotate about a fixed mast and ornithopters in which lift is generated by flapping wings.A powered...

, gliders

Glider aircraft

Glider aircraft are heavier-than-air craft that are supported in flight by the dynamic reaction of the air against their lifting surfaces, and whose free flight does not depend on an engine. Mostly these types of aircraft are intended for routine operation without engines, though engine failure can...

, autogiros, helicopter

Helicopter

A helicopter is a type of rotorcraft in which lift and thrust are supplied by one or more engine-driven rotors. This allows the helicopter to take off and land vertically, to hover, and to fly forwards, backwards, and laterally...

s, and dirigibles. These speeds are derived from data obtained by aircraft designers and manufacturers during flight testing and verified in most countries by government flight inspectors during aircraft type-certification

Type certificate

A Type Certificate, is awarded by aviation regulating bodies to aerospace manufacturers after it has been established that the particular design of a civil aircraft, engine, or propeller has fulfilled the regulating bodies' current prevailing airworthiness requirements for the safe conduct of...

 testing. Using them is considered a best practice

Best practice

A best practice is a method or technique that has consistently shown results superior to those achieved with other means, and that is used as a benchmark...

 to maximize aviation safety, aircraft performance or both.

The actual speeds represented by these designators are specific to a particular model of aircraft, and are expressed in terms of the aircraft's indicated airspeed

Indicated airspeed

Indicated airspeed is the airspeed read directly from the airspeed indicator on an aircraft, driven by the pitot-static system. IAS is directly related to calibrated airspeed , which is the IAS corrected for instrument and installation errors....

, so that pilots may use them directly, without having to apply correction factors.

In general aviation aircraft, the most commonly used and most safety-critical airspeeds are displayed as color-coded arcs and lines located on the face of an aircraft's airspeed indicator

Airspeed indicator

The airspeed indicator or airspeed gauge is an instrument used in an aircraft to display the craft's airspeed, typically in knots, to the pilot.- Use :...

. The lower ends of the green arc and the white arc are the stalling speed with wing flaps retracted, and stalling speed with wing flaps fully extended, respectively. These are the stalling speeds for the aircraft at its maximum weight.

Proper display of V speeds is an airworthiness requirement for type-certificated aircraft in most countries.

Regulation

The most common V-speeds are often defined by a particular government's aviation regulation

Aviation law

Aviation law is the branch of law that concerns flight, air travel, and associated legal and business concerns. Some of its area of concern overlaps that of admiralty law and in many cases, aviation law is considered a matter of international law due to the nature of air travel. However, the...

s. In the United States, these are defined in title 14 of the United States Code of Federal Regulations

Code of Federal Regulations

The Code of Federal Regulations is the codification of the general and permanent rules and regulations published in the Federal Register by the executive departments and agencies of the Federal Government of the United States.The CFR is published by the Office of the Federal Register, an agency...

, known as the Federal Aviation Regulations

Federal Aviation Regulations

The Federal Aviation Regulations, or FARs, are rules prescribed by the Federal Aviation Administration governing all aviation activities in the United States. The FARs are part of Title 14 of the Code of Federal Regulations...

 or FARs. In Canada

Canada

Canada is a North American country consisting of ten provinces and three territories. Located in the northern part of the continent, it extends from the Atlantic Ocean in the east to the Pacific Ocean in the west, and northward into the Arctic Ocean...

, the regulatory body, Transport Canada

Transport Canada

Transport Canada is the department within the government of Canada which is responsible for developing regulations, policies and services of transportation in Canada. It is part of the Transportation, Infrastructure and Communities portfolio...

, defines 26 commonly used V-speeds in their Aeronautical Information Manual (AIM).

Regulatory V-speeds

These V-speeds are defined by regulations.

V-speed designator	Description
V1	Critical engine failure recognition speed. (See V1 definitions below)
V2	Takeoff safety speed. The speed at which the aircraft may safely become airborne with one engine inoperative.
V2min	Minimum takeoff safety speed.
V3	Flap retraction speed.
V4	Steady initial climb speed. The all engines operating take-off climb speed used to the point where acceleration to flap retraction speed is initiated. Should be attained by a gross height of 400 feet.
VA	Design maneuvering speed Maneuvering speed In aviation, maneuvering speed is the maximum speed where full, abrupt control movement in the pitch axis will result in an aerodynamic stall of the aircraft prior to exceeding the design load limit. It has been widely misunderstood that flight below maneuvering speed will provide total protection... , also known as the "Speed for maximum control deflection." This is the speed above which it is unwise to make full application of any single flight control (or "pull to the stops") as it may generate a force greater than the aircraft's structural limitations. The heavier an aircraft is loaded the faster this speed.
Vat	Indicated airspeed at threshold, which is equal to the stall speed VS0 multiplied by 1.3 or stall speed VS1g multiplied by 1.23 in the landing configuration at the maximum certificated landing mass. If both VS0 and VS1g are available, the higher resulting Vat shall be applied.
VB	Design speed for maximum gust intensity.
VC	Design cruising speed, also known as the optimum cruise speed, is the most efficient speed in terms of distance, speed and fuel usage.
Vcef	See V1; generally used in documentation of military aircraft performance.
VD	Design diving speed.
VDF	Demonstrated flight diving speed.
VEF	The speed at which the Critical engine Critical engine The critical engine of a multi-engine, fixed-wing aircraft is the one whose failure would result in the most adverse effects on the aircraft's handling and performance.- Description :...  is assumed to fail during takeoff.
VF	Designed flap speed.
VFC	Maximum speed for stability characteristics.
VFE	Maximum flap extended speed.
VFTO	Final takeoff speed.
VH	Maximum speed in level flight at maximum continuous power.
VLE	Maximum landing gear extended speed. This is the maximum speed at which it is safe to fly a retractable gear aircraft with the landing gear extended.
VLO	Maximum landing gear operating speed. This is the maximum speed at which it is safe to extend or retract the landing gear on a retractable gear aircraft.
VLOF	Lift-off speed.
VMC	Minimum control speed with Critical engine Critical engine The critical engine of a multi-engine, fixed-wing aircraft is the one whose failure would result in the most adverse effects on the aircraft's handling and performance.- Description :...  inoperative.
Vmca	Minimum control speed in the take-off configuration – the minimum calibrated airspeed at which the aircraft is directionally controllable in flight with a sudden Critical engine Critical engine The critical engine of a multi-engine, fixed-wing aircraft is the one whose failure would result in the most adverse effects on the aircraft's handling and performance.- Description :...  failure and takeoff power on the operative engine(s).
Vmcg	Minimum control speed on the ground - the minimum airspeed at which the aircraft is directionally controllable during acceleration along the runway with one engine inoperative, takeoff power on the operative engine(s), and with nose wheel steering assumed inoperative.
Vmcl	Minimum control speed in the landing configuration with one engine inoperative.
VMO	Maximum operating limit speed.
VMU	Minimum unstick speed.
VNE	Never exceed speed.
VNO	Maximum structural cruising speed or maximum speed for normal operations.
VR	Rotation Takeoff Takeoff is the phase of flight in which an aerospace vehicle goes from the ground to flying in the air.For horizontal takeoff aircraft this usually involves starting with a transition from moving along the ground on a runway. For balloons, helicopters and some specialized fixed-wing aircraft , no...  speed. The speed at which the aircraft's nosewheel Tricycle gear Tricycle gear describes an aircraft undercarriage, or landing gear, arranged in a tricycle fashion. The tricycle arrangement has one wheel in the front, called the nose wheel, and two or more main wheels slightly aft of the center of gravity...  leaves the ground. Also see note on Vref below.
Vrot	Used instead of VR (in discussions of the takeoff performance of military aircraft) to denote rotation speed in conjunction with the term Vref (refusal speed).
VRef	Landing reference speed or threshold crossing speed. In discussions of the takeoff performance of military aircraft, the term Vref stands for refusal speed. Refusal speed is the maximum speed during takeoff from which the air vehicle can stop within the available remaining runway length for a specified altitude, weight, and configuration. Incorrectly, or as an abbreviation, some documentation refers to Vref and/or Vrot speeds as "Vr."
VS	Stall speed or minimum steady flight speed for which the aircraft is still controllable.
VS0	Stall speed or minimum flight speed in landing configuration.
VS1	Stall speed or minimum steady flight speed for which the aircraft is still controllable in a specific configuration.
VSR	Reference stall speed.
VSR0	Reference stall speed in landing configuration.
VSR1	Reference stall speed in a specific configuration.
VSW	Speed at which the stall warning will occur.
VTOSS	Category A rotorcraft takeoff safety speed.
VX	Speed that will allow for best angle of climb Angle of Climb In aerodynamics, angle of climb is the ratio between distance travelled over the ground and altitude gained. The angle of climb can be expressed as the angle between a plane horizontal to the Earth's surface and the actual flight path followed by the aircraft during its ascent... .
VY	Speed that will allow for the best rate of climb Rate of climb In aeronautics, the rate of climb is an aircraft's vertical speed - the rate of change in altitude. In most ICAO member countries , this is usually expressed in feet per minute and can be abbreviated as ft/min. Elsewhere, it is commonly expressed in metres per second, abbreviated as m/s... .

Other V-speeds

Some of these V-speeds are specific to particular types of aircraft and are not defined by regulations.

V-speed designator	Description
VBE	Best endurance speed – the speed that gives the greatest airborne time for fuel consumed. This may be used when there is reason to remain aloft for an extended period, such as waiting for a forecast improvement in weather on the ground.
VBG	Best power-off glide speed – the speed that provides maximum lift-to-drag Drag (physics) In fluid dynamics, drag refers to forces which act on a solid object in the direction of the relative fluid flow velocity...  ratio and thus the greatest gliding distance available.
VBR	Best range speed – the speed that gives the greatest range for fuel consumed - often identical to Vmd.
VFS	Final segment of a departure with one powerplant failed.
Vimd	Minimum drag Drag (physics) In fluid dynamics, drag refers to forces which act on a solid object in the direction of the relative fluid flow velocity...
Vimp	Minimum power
VLLO	Maximum landing light operating speed – for aircraft with retractable landing lights.
Vmbe	Maximum brake energy speed
Vmd	Minimum drag Drag (physics) In fluid dynamics, drag refers to forces which act on a solid object in the direction of the relative fluid flow velocity...  (per lift Lift (force) A fluid flowing past the surface of a body exerts a surface force on it. Lift is the component of this force that is perpendicular to the oncoming flow direction. It contrasts with the drag force, which is the component of the surface force parallel to the flow direction... ) - often identical to VBR. (alternatively same as Vimd)
Vmin	Minimum speed for instrument flight (IFR Instrument flight rules Instrument flight rules are one of two sets of regulations governing all aspects of civil aviation aircraft operations; the other are visual flight rules .... ) for helicopters
Vmp	Minimum power
Vp	Aquaplaning speed
VPD	Maximum speed at which whole-aircraft parachute Ballistic Recovery Systems Ballistic Recovery Systems is a manufacturer of aircraft ballistic parachutes .The company was formed in 1980 by Boris Popov after he survived a fall in a partly collapsed hang glider in 1975...  deployment has been demonstrated
Vra	Rough air speed (turbulence penetration speed).
VSL	stall speed in a specific configuration
Vs1g	stall speed at maximum lift coefficient
Vsse	Safe single engine speed
Vt	Threshold speed
Vtocs	Take-off climbout speed (helicopters)
Vtos	Minimum speed for a positive rate of climb with one engine inoperative
Vtmax	Max threshold speed
Vwo	Maximum window or canopy open operating speed
VXSE	Best angle of climb speed with a single operating engine in a light, twin-engine aircraft – the speed that provides the most altitude gain per unit of horizontal distance following an engine failure.
VYSE	Best rate of climb speed with a single operating engine in a light, twin-engine aircraft – the speed that provides the most altitude gain per unit of time following an engine failure.
VZRC	Zero rate of climb speed in a twin-engine aircraft

Mach numbers

Whenever a limiting speed is expressed in terms of Mach number, it is expressed as an "M speed", e.g. V_MO: Maximum operating limit speed (in knots), M_MO: Maximum operating limit Mach.

V₁ definitions

V₁ is the critical engine failure recognition speed or takeoff decision speed. It is the decision speed nominated by the pilot which satisfies all safety rules, and above which the takeoff will continue even if an engine fails. The speed will vary between aircraft types and also due to aircraft weight, runway length, wing flap

Flap (aircraft)

Flaps are normally hinged surfaces mounted on the trailing edges of the wings of a fixed-wing aircraft to reduce the speed an aircraft can be safely flown at and to increase the angle of descent for landing without increasing air speed. They shorten takeoff and landing distances as well as...

 setting, engine thrust used, runway surface contamination and other factors.

V₁ is defined differently in different jurisdictions:

• The US Federal Aviation Administration
  Federal Aviation Administration
  The Federal Aviation Administration is the national aviation authority of the United States. An agency of the United States Department of Transportation, it has authority to regulate and oversee all aspects of civil aviation in the U.S...
  
   defines it as: V1 means the maximum speed in the takeoff at which the pilot must take the first action (e.g., apply brakes, reduce thrust, deploy speed brakes) to stop the airplane within the accelerate-stop distance. V1 also means the minimum speed in the takeoff, following a failure of the critical engine at VEF, at which the pilot can continue the takeoff and achieve the required height above the takeoff surface within the takeoff distance.

• Transport Canada
  Transport Canada
  Transport Canada is the department within the government of Canada which is responsible for developing regulations, policies and services of transportation in Canada. It is part of the Transportation, Infrastructure and Communities portfolio...
  
  defines it as: Critical engine failure recognition speed and adds: This definition is not restrictive. An operator may adopt any other definition outlined in the aircraft flight manual (AFM) of TC type-approved aircraft as long as such definition does not compromise operational safety of the aircraft.