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A single-engined Cessna 150L's airspeed indicator indicating its V-speeds in knots

In aviation, V-speeds are standard terms used to define airspeeds important or useful to the operation of all aircraft.[1] These speeds are derived from data obtained by aircraft designers and manufacturers during flight testing for aircraft type-certification. Using them is considered a best practice to maximize aviation safety, aircraft performance, or both.[2]

The actual speeds represented by these designators are specific to a particular model of aircraft. They are expressed by the aircraft's indicated airspeed (and not by, for example, the ground speed), so that pilots may use them directly, without having to apply correction factors, as aircraft instruments also show indicated airspeed.

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. The lower ends of the white arc and the green arc are the stalling speed with wing flaps in landing configuration, and stalling speed with wing flaps retracted, respectively. These are the stalling speeds for the aircraft at its maximum weight.[3][4] The yellow band is the range in which the aircraft may be operated in smooth air, and then only with caution to avoid abrupt control movement. The red line is the VNE, the never-exceed speed.

Proper display of V-speeds is an airworthiness requirement for type-certificated aircraft in most countries.[5][6]

Regulations

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The most common V-speeds are often defined by a particular government's aviation regulations. In the United States, these are defined in title 14 of the United States Code of Federal Regulations, known as the Federal Aviation Regulations (FARs).[7] In Canada, the regulatory body, Transport Canada, defines 26 commonly used V-speeds in their Aeronautical Information Manual.[8] V-speed definitions in FAR 23, 25 and equivalent are for designing and certification of airplanes, not for their operational use. The descriptions below are for use by pilots.

Regulatory V-speeds

[edit]

These V-speeds are defined by regulations. They are typically defined with constraints such as weight, configuration, or phases of flight. Some of these constraints have been omitted to simplify the description.

V-speed designator Description
V1 The speed beyond which takeoff should no longer be aborted (or "the point of no return") (see § V1 definitions below).[7][8][9]
V2 Takeoff safety speed. The speed at which the aircraft may safely climb with one engine inoperative.[7][8][9]
V2min Minimum takeoff safety speed.[7][8][9]
V3 Flap retraction speed.[8][9]
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 ft (120 m).[10]
VA Design maneuvering speed. 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.[7][8][9][11]
Vat Indicated airspeed at threshold, which is usually 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, though some manufacturers apply different criteria. If both VS0 and VS1g are available, the higher resulting Vat shall be applied.[12] Also called "approach speed". Also known as Vth[13][14]

Davies defines Vat and Vref as equivalent.[15]

VB Design speed for maximum gust intensity.[7][8][9]
VC Design cruise, also known as the optimum cruise speed, is the most efficient speed in terms of distance, speed and fuel usage.[16][17][18]
Vcef See V1; generally used in documentation of military aircraft performance. Denotes "critical engine failure" speed as the speed during takeoff where the same distance would be required to either continue the takeoff or abort to a stop.[19]
VD Design diving speed, the highest speed planned to be achieved in testing.[7][8][9]
VDF Demonstrated flight diving speed, the highest actual speed achieved in testing.[7][8][9]
VEF The speed at which the critical engine is assumed to fail during takeoff.[7]
VF Designed flap speed.[7][8][9]
VFC Maximum speed for stability characteristics.[7][9]
VFE Maximum flap extended speed.[7][8][9]
VFTO Final takeoff speed.[7]
VH Maximum speed in level flight at maximum continuous power.[7][8][9]
VLE Maximum landing gear extended speed. This is the maximum speed at which a retractable gear aircraft should be flown with the landing gear extended.[7][8][9][20]
VLO Maximum landing gear operating speed. This is the maximum speed at which the landing gear on a retractable gear aircraft should be extended or retracted.[7][9][20]
VLOF Lift-off speed.[7][9]
VMC Minimum control speed. The minimum speed at which the aircraft is still controllable with the critical engine inoperative.[7] Like the stall speed, there are several important variables that are used in this determination. Refer to the minimum control speed article for a thorough explanation. VMC is sometimes further refined into more discrete V-speeds e.g. VMCA,VMCG.
VMCA Minimum control speed air. The minimum speed that the aircraft is still controllable with the critical engine inoperative[21] while the aircraft is airborne. VMCA is sometimes simply referred to as VMC.
VMCG Minimum control speed ground. The minimum speed that the aircraft is still controllable with the critical engine inoperative[21] while the aircraft is on the ground.
VMCL Minimum control speed in the landing configuration with one engine inoperative.[9][21]
VMO Maximum operating limit speed.[7][8][9] Exceeding VMO may trigger an overspeed alarm.[22]
VMU Minimum unstick speed.[7][8][9]
VNE Never exceed speed.[7][8][9][23] In a helicopter, this is chosen to prevent retreating blade stall and prevent the advancing blade from going supersonic.
VNO Maximum structural cruising speed or maximum speed for normal operations. Speed at which exceeding the limit load factor may cause permanent deformation of the aircraft structure.[7][8][9][24]
VO Maximum operating maneuvering speed.[25]
VR Rotation speed. The speed at which the pilot begins to apply control inputs to cause the aircraft nose to pitch up, after which it will leave the ground.[7][26][Note 1]
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).[19]
VRef Landing reference speed or threshold crossing speed.[7][8][9] Must be at least 1.3 VS0. Must be at least VMC for reciprocating-engine aircraft, or 1.05 VMC for commuter category aircraft.[28]

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.[19] Incorrectly, or as an abbreviation, some documentation refers to Vref and/or Vrot speeds as "Vr."[29]

VS Stall speed or minimum steady flight speed for which the aircraft is still controllable.[7][8][9]
VS0 Stall speed or minimum flight speed in landing configuration.[7][8][9]
VS1 Stall speed or minimum steady flight speed for which the aircraft is still controllable in a specific configuration.[7][8]
VSR Reference stall speed.[7]
VSR0 Reference stall speed in landing configuration.[7]
VSR1 Reference stall speed in a specific configuration.[7]
VSW Speed at which the stall warning will occur.[7]
VTOSS Category A rotorcraft takeoff safety speed.[7][23]
VX Speed that will allow for best angle of climb.[7][8]
VY Speed that will allow for the best rate of climb.[7][8]

Other V-speeds

[edit]

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

V-speed designator Description
VAPP Approach speed. Speed used during final approach with landing flap set.[30] VREF plus safety increment,[31][32][33] typically minimum 5 knots,[34] and maximum 15 knots[30] to avoid exceeding flap limiting speeds. Typically it is calculated as half the headwind component plus the gust factor.[30] The purpose is to ensure that turbulence or gusts will not result in the airplane flying below VREF at any point on the approach.[30] Also known as VFLY.
VBE Best endurance speed – the speed that gives the greatest airborne time for fuel consumed.[citation needed]
VBG Best power-off glide speed – the speed that provides maximum lift-to-drag 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.[35]
VFS Final segment of a departure with one powerplant failed.[36]
Vimd Minimum drag[37]
Vimp Minimum power[37]
VLLO Maximum landing light operating speed – for aircraft with retractable landing lights.[9]
VLS Lowest selectable speed[38]
Vmbe Maximum brake energy speed[37][39]
Vmd Minimum drag (per lift) – often identical to VBE.[35][39] (alternatively same as Vimd[40])
Vmin Minimum speed for instrument flight (IFR) for helicopters[23]
Vmp Minimum power[39]
Vms Minimum sink speed at median wing loading – the speed at which the minimum descent rate is obtained. In modern gliders, Vms and Vmc have evolved to the same value.[41]
Vp Aquaplaning speed[39]
VPD Maximum speed at which whole-aircraft parachute deployment has been demonstrated[42]
Vra Rough air speed (turbulence penetration speed).[9]
VSL Stall speed in a specific configuration[9][39]
Vs1g Stall speed at 1g load factor[43]
Vsse Safe single-engine speed[44]
Vt Threshold speed[39]
VTD Touchdown speed[45]
VTGT Target speed[citation needed]
VTO Take-off speed. (see also VLOF)[46]
Vtocs Take-off climbout speed (helicopters)[23]
Vtos Minimum speed for a positive rate of climb with one engine inoperative[39]
Vtmax Max threshold speed[39][47]
Vwo Maximum window or canopy open operating speed[48]
VXSE Best angle of climb speed with one engine inoperative (OEI) in a light, twin-engine aircraft – the speed that provides the most altitude gain per unit of horizontal distance following an engine failure, while maintaining a small bank angle that should be presented with the engine-out climb performance data.[44]
VYSE Best rate of climb speed with one engine inoperative (OEI) in a light, twin-engine aircraft – the speed that provides the most altitude gain per unit of time following an engine failure, while maintaining a small bank angle that should be presented with the engine-out climb performance data.[20][44]
VZF Minimum zero flaps speed[49]
VZRC Zero rate of climb speed. The aircraft is at sufficiently low speed on the "back of the drag curve" that it cannot climb, accelerate, or turn, so must reduce drag.[39] The aircraft cannot be recovered without loss of height.[15]: 144–145 

Mach numbers

[edit]

Whenever a limiting speed is expressed by a Mach number, it is expressed relative to the local speed of sound, e.g. VMO: Maximum operating speed, MMO: Maximum operating Mach number.[7][8]

V1 definitions

[edit]

V1 is the critical engine failure recognition speed or takeoff decision speed. It is the speed above which the takeoff will continue even if an engine fails or another problem occurs, such as a blown tire.[9] The speed will vary among aircraft types and varies according to factors such as aircraft weight, runway length, wing flap setting, engine thrust used and runway surface contamination; thus, it must be determined by the pilot before takeoff. Aborting a takeoff after V1 is strongly discouraged because the aircraft may not be able to stop before the end of the runway, thus suffering a runway overrun.[50]

V1 is defined differently in different jurisdictions, and definitions change over time as aircraft regulations are amended.

  • The US Federal Aviation Administration and the European Union Aviation Safety Agency define it as: "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."[7] V1 thus includes reaction time.[26] In addition to this reaction time, a safety margin equivalent to 2 seconds at V1 is added to the accelerate-stop distance.[51][52]
  • Transport Canada 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."[8]

See also

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Notes

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References

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Further reading

[edit]
Revisions and contributorsEdit on WikipediaRead on Wikipedia

V speeds

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from Grokipedia
V-speeds are standardized abbreviations used in aviation to denote specific airspeeds that are critical for performance, limitations, and safe operation during various flight phases, as defined in the U.S. (14 CFR § 1.2). These speeds, expressed primarily as indicated airspeeds (IAS) for pilot reference on the , are determined through rigorous during certification and vary based on factors such as weight, configuration (e.g., flaps or gear extended), altitude, , and wind conditions. They serve as essential benchmarks to prevent structural damage, ensure , and optimize performance, with over 30 distinct V-speeds outlined in regulations to cover scenarios from takeoff to never-exceed limits. Among the most notable V-speeds are those related to takeoff and climb, such as V1, the maximum speed at which the pilot must abort takeoff or the minimum speed to continue after an engine failure. This definition underscores that, in practice for transport category aircraft including the Airbus A320, rejected takeoffs occur only before V1, with continuation mandatory thereafter except in extraordinary circumstances posing greater risk than proceeding; VR, the speed for achieving takeoff attitude; and V2, the safe climb speed post-takeoff. For and low-speed handling, VS represents the stalling speed in a given configuration, while VS0 specifies the speed in landing setup, both crucial for avoiding loss of lift during approach and landing. Maneuvering and structural limits include VA, the design where full control inputs induce before damage; VNO, the maximum structural cruising speed; and VNE, the never-exceed speed beyond which structural integrity is at risk. Configuration-specific speeds like VFE (maximum flap extended) and VLE (maximum extended) protect components from aerodynamic loads, while multi-engine aircraft emphasize VMC, the minimum control speed with one engine inoperative to maintain . Climb performance is guided by VX for best angle (maximizing altitude over distance) and VY for best rate (maximizing altitude gain per time), often adjusted for single-engine scenarios in twins as VXSE and VYSE. The use of V-speeds is mandated in aircraft flight manuals (AFM/POH) and applies under standard conditions like sea-level pressure and unless otherwise noted, enabling pilots to make informed decisions that enhance safety and efficiency across all types from light singles to large transports. By standardizing these values, regulatory bodies like the FAA ensure interoperability and risk mitigation, with deviations requiring specific calculations or limitations to account for real-world variables.

Fundamentals

Definition and Purpose

V speeds, derived from the French word "vitesse" meaning "speed," refer to a standardized set of indicated airspeeds (IAS) that denote critical performance thresholds for during specific flight conditions and configurations. These speeds are expressed in knots and displayed on the 's airspeed indicator, serving as essential references for pilots to maintain safe and efficient operations. Unlike (TAS), which accounts for atmospheric variations, or , which incorporates wind effects, V speeds are calibrated as IAS to provide consistent, instrument-based guidance independent of external factors. The concept of V speeds originated in early 20th-century aviation as engineers and regulators sought uniform terminology for aircraft performance limits, with the "V" notation borrowed from French aviation pioneers. This system evolved through international standardization efforts, particularly via the International Civil Aviation Organization (ICAO) Annex 6 on Operation of Aircraft and national codes like the U.S. Federal Aviation Regulations (14 CFR Part 1), which formally define over 30 V speeds based on flight testing and certification data. These evolutions reflect ongoing refinements to address advancements in aircraft design and operational safety. V speeds play a pivotal role in by delineating limits that prevent structural damage, such as exceeding never-exceed speeds, and ensure aerodynamic controllability, like during engine failure. They optimize key flight phases, including takeoff for achieving safe climb gradients, en route cruising to avoid flutter or gust-induced loads, and to minimize touchdown speeds while maintaining maneuverability. By providing these benchmarks, V speeds enable pilots to make informed decisions that enhance overall aircraft performance and mitigate risks. Each V speed is inherently aircraft-specific, calculated during type certification using factors such as gross weight, center of gravity position, flap settings, and environmental conditions like density altitude. For instance, takeoff-related V speeds may vary significantly between a light general aviation aircraft and a heavy jet transport due to differences in thrust-to-weight ratios and wing loading. Pilots consult the aircraft's flight manual or performance charts to determine these values for each flight, ensuring compliance with certified limits.

Notation and Measurement

V speeds employ a standardized where the letter "V," derived from the French word vitesse meaning speed, is followed by a subscript or letter to denote the specific parameter. For example, VSV_S represents the stall speed or minimum steady flight speed at which the remains controllable, while V1V_1 indicates the maximum speed during takeoff at which the pilot must initiate an abort procedure. More precise variants include subscripts for configuration, such as VS0V_{S0} for the stall speed in landing configuration with full flaps and extended. These notations are formally defined in regulations, ensuring consistency across aircraft types and operations. V speeds are measured and expressed as indicated airspeed (IAS), which is the direct reading from the aircraft's derived from the pitot-static system. The captures ram air pressure (total pressure), while static ports measure ambient ; the difference yields , which the instrument converts to IAS. This system is calibrated during to account for installation errors and instrument inaccuracies, but IAS readings require adjustment in performance calculations for non-standard conditions like altitude and temperature, which affect air density and thus true aerodynamic effects. IAS is preferred for V speeds over true airspeed (TAS) because it allows pilots to reference values directly from the instrument without real-time conversions, simplifying operational use during critical phases of flight. TAS, which equals IAS corrected for , is more representative of actual motion through the air but is not directly displayed; at higher speeds, effects near Mach 1 necessitate additional considerations like or limits, though core V speeds remain IAS-based for most subsonic operations. In aviation documentation, V speeds are primarily expressed in knots (kts), aligning with international standards for airspeed measurement. This unit, equivalent to nautical miles per hour, facilitates precise navigation and performance planning. Older aircraft manuals or historical texts may occasionally use miles per hour (mph), reflecting earlier U.S. conventions before widespread adoption of knots.

Regulatory Framework

Certification Standards

V speeds are integral to aircraft certification under international and national airworthiness standards, which mandate their determination and demonstration to ensure safe performance across various flight phases. The Federal Aviation Administration (FAA) in the United States specifies V speeds in 14 CFR Part 23 for normal-category airplanes, typically those with up to 19 passenger seats and a maximum takeoff weight of 19,000 pounds, and in 14 CFR Part 25 for transport-category airplanes exceeding these limits. Similarly, the European Union Aviation Safety Agency (EASA) outlines requirements in Certification Specifications (CS) CS-23 for normal, utility, aerobatic, and commuter aeroplanes, and CS-25 for large aeroplanes, harmonizing closely with FAA rules to facilitate bilateral agreements. The International Civil Aviation Organization (ICAO) provides overarching guidance through Annex 8, which establishes minimum airworthiness standards that member states must implement, including performance-based requirements for speeds critical to flight safety, though detailed V speed definitions are elaborated in national codes. Aircraft manufacturers demonstrate compliance with these V speed standards through rigorous certification processes involving flight testing, as detailed in FAA Advisory Circulars AC 23-8C for Part 23 airplanes and AC 25-7D for Part 25 transports. These tests include stall speed determinations in various configurations (§ 23.2110 and § 25.103), where the aircraft is flown at idle power to identify the reference stall speed (VSR) under 1-g conditions, ensuring margins for recovery without excessive altitude loss. Gust load evaluations, per structural requirements like § 25.341, simulate turbulent conditions to verify that V speeds account for dynamic loads without compromising control or integrity. Takeoff and landing demonstrations further validate speeds such as minimum control speeds (VMC) and approach reference speeds (VREF), often requiring multiple runs to establish safety margins under engine-out scenarios. The standards governing V speeds have evolved significantly since the advent of the in the 1950s, when initial transport regulations were adapted from propeller-era rules to address higher speeds and thrust asymmetries in turbine-powered aircraft, leading to formalized definitions in early versions of Part 25 around 1953. Subsequent amendments incorporated supersonic and advanced aerodynamic considerations, with major updates in the 1970s-1980s refining and maneuvering speeds for improved . In the , amendments like FAA Amendment 23-64 (effective August 30, 2017) introduced performance-based rules under Part 23 to accommodate electric vertical takeoff and landing () aircraft. In the , further developments include the FAA's Powered-Lift Integration rule (published November 21, 2024, effective January 21, 2025), which integrates operational and performance standards for powered-lift aircraft, requiring data such as climb rates and takeoff/landing distances in the flight manual to ensure compatibility with traditional certification frameworks, though without defining specific V speeds. EASA paralleled the 2017 FAA changes with CS-23 Amendment 5 (issued April 5, 2017), emphasizing simplified testing for light electric aeroplanes. Differences in V speed requirements reflect the scale and complexity of : Part 23 and CS-23 provide simplified mandates for , focusing on basic speeds like (VS) and takeoff safety margins with fewer multi-engine contingencies, suitable for lighter, lower-speed operations up to 250 knots . In contrast, Part 25 and CS-25 impose more intricate standards for large transports, mandating detailed speeds such as decision speed (V1), rotation speed (VR), and climb speed (V2) to handle high-thrust failures and all-engine-out scenarios, with stricter gust and testing to support operations at speeds exceeding 300 knots. This bifurcation ensures proportionality in rigor while maintaining between authorities.

Sources and Variations by Authority

The (FAA) defines V speeds primarily through 14 CFR Part 1, which provides standardized abbreviations and terms applicable across operations, while requirements for specific V speeds are detailed in Parts 23 (normal, , acrobatic, and commuter category airplanes), 25 ( category airplanes), 27 (normal category rotorcraft), and 29 ( category rotorcraft). These regulations tie V speeds directly to the aircraft's basis, ensuring they reflect design limits, performance capabilities, and safety margins during testing and approval processes. For instance, Part 25 specifies performance-based V speeds like V1 (takeoff decision speed) and V2 (takeoff safety speed) as integral to demonstrating safe operation under engine failure conditions. The (EASA) and the (ICAO) adopt definitions for V speeds that are largely harmonized with FAA standards but incorporate influences in documentation and some operational contexts, such as using kilometers per hour alongside knots in certain advisory materials. EASA's Certification Specifications (CS), particularly CS-23 for small aeroplanes and CS-25 for large aeroplanes, mirror FAR Parts 23 and 25 in defining key V speeds like VR ( speed) as the speed at which the pilot applies control inputs to reach takeoff attitude. Post-Brexit alignments have seen the (CAA) maintain close synchronization with EASA CS through bilateral agreements, minimizing divergences in V speed applications for certified aircraft. ICAO Annex 8 provides overarching airworthiness principles but defers detailed V speed definitions to national authorities, emphasizing consistency in global certification, with Amendment 110 (applicable November 26, 2026) updating general airworthiness provisions such as landing performance data. Other authorities, such as under the Canadian Aviation Regulations (), align V speeds closely with FAA definitions while incorporating operational nuances in guidance documents; for example, CAR 571 and related standards reference V speeds like VA () as the maximum speed for full control deflection without structural overload. The (CASA) in follows ICAO standards through Part 21 of the Civil Aviation Safety Regulations (CASR), defining V speeds in advisory publications like CAAP 5.23-1, which lists terms such as V1 (takeoff decision speed) and Vyse (best single-engine climb speed) consistent with international norms but tailored to Australian environmental conditions. Some European documents introduce unique notations, such as VR for rotation speed in , which may vary slightly in application for or hybrid operations compared to pure fixed-wing definitions. Harmonization efforts trace back to the (JAA), whose Joint Aviation Requirements (JAR-25) were developed in the 1990s to align with FAA FAR-25, reducing certification discrepancies through working groups like the Aviation Rulemaking Advisory Committee (ARAC). This legacy facilitated the transition to EASA CS, promoting global alignment in V speed definitions and testing protocols.

Design and Limit Speeds

Structural Speeds

Structural speeds encompass the airspeeds that define the aerodynamic and load limits of an aircraft's , ensuring it can endure expected forces without deformation or failure during under standards like 14 CFR Part 25. These speeds form the foundation for structural design, protecting against gusts, maneuvers, and high-speed phenomena such as flutter, while establishing operational boundaries marked on the indicated. The , VAV_A, is the maximum at which abrupt full control deflections can be applied without exceeding the 's limit load factor, causing it to before structural overload. It is derived from the VA=VSnV_A = V_S \sqrt{n}
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