![ASI01b](https://upload.wikimedia.org/wikipedia/commons/8/83/ASI01b.jpg)
In
aviation
Aviation includes the activities surrounding mechanical flight and the aircraft industry. ''Aircraft'' includes fixed-wing and rotary-wing types, morphable wings, wing-less lifting bodies, as well as lighter-than-air craft such as hot air ...
, V-speeds are standard terms used to define
airspeed
In aviation, airspeed is the speed of an aircraft relative to the air. Among the common conventions for qualifying airspeed are:
* Indicated airspeed ("IAS"), what is read on an airspeed gauge connected to a Pitot-static system;
* Calibrated ...
s important or useful to the operation of all
aircraft
An aircraft is a vehicle that is able to fly by gaining support from the air. It 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 ...
.
These speeds are derived from data obtained by aircraft designers and manufacturers during
flight testing
Flight testing is a branch of aeronautical engineering that develops specialist equipment required for testing aircraft behaviour and systems. Instrumentation systems are developed using proprietary transducers and data acquisition systems. D ...
for aircraft
type-certification. Using them is considered a
best practice
A best practice is a method or technique that has been generally accepted as superior to other known alternatives because it often produces results that are superior to those achieved by other means or because it has become a standard way of doing ...
to maximize
aviation safety
Aviation safety is the study and practice of managing risks in aviation. This includes preventing aviation accidents and incidents through research, educating air travel personnel, passengers and the general public, as well as the design of airc ...
, aircraft performance, or both.
The actual speeds represented by these designators are specific to a particular model of aircraft. They are expressed by the aircraft's
indicated airspeed
Indicated airspeed (IAS) is the airspeed of an aircraft as measured by its pitot-static system and displayed by the airspeed indicator (ASI). This is the pilots' primary airspeed reference.
This value is not corrected for installation error, i ...
(and not by, for example, the
ground speed
Ground speed is the horizontal speed of an aircraft relative to the Earth’s surface. It is vital for accurate navigation that the pilot has an estimate of the ground speed that will be achieved during each leg of a flight.
An aircraft diving ve ...
), 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 airspeed indicator (ASI) or airspeed gauge is a flight instrument indicating the airspeed of an aircraft in kilometers per hour (km/h), knots (kn), miles per hour (MPH) and/or meters per second (m/s). The recommendation by ICAO is to use km ...
. 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.
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 V
NE, the never-exceed speed.
Proper display of V-speeds is an airworthiness requirement for type-certificated aircraft in most countries.
Regulations
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
In the law of the United States, the ''Code of Federal Regulations'' (''CFR'') is the codification of the general and permanent regulations promulgated by the executive departments and agencies of the federal government of the United States. ...
, known as the
Federal Aviation Regulations
The Federal Aviation Regulations (FARs) are rules prescribed by the Federal Aviation Administration (FAA) governing all aviation activities in the United States. The FARs comprise Title 14 of the Code of Federal Regulations (CFR). A wide variety ...
(FARs).
In
Canada
Canada is a country in North America. Its ten provinces and three territories extend from the Atlantic Ocean to the Pacific Ocean and northward into the Arctic Ocean, covering over , making it the world's second-largest country by tot ...
, the regulatory body,
Transport Canada
Transport Canada (french: Transports Canada) is the department within the Government of Canada responsible for developing regulations, policies and services of road, rail, marine and air transportation in Canada. It is part of the Transportati ...
, defines 26 commonly used V-speeds in their Aeronautical Information Manual.
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
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.
Other V-speeds
Some of these V-speeds are specific to particular types of aircraft and are not defined by regulations.
Mach numbers
Whenever a limiting speed is expressed by a
Mach number, it is expressed relative to the local speed of sound, e.g. V
MO: Maximum operating speed, M
MO: Maximum operating Mach number.
V1 definitions
V
1 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.
The speed will vary among aircraft types and varies according to factors such as aircraft weight, runway length,
wing flap
A flap is a high-lift device used to reduce the stalling speed of an aircraft wing at a given weight. Flaps are usually mounted on the wing trailing edges of a fixed-wing aircraft. Flaps are used to reduce the take-off distance and the landin ...
setting, engine thrust used and runway surface contamination, thus it must be determined by the pilot before takeoff. Aborting a takeoff after V
1 is strongly discouraged because the aircraft may not be able to stop before the end of the runway, thus suffering a
runway overrun
A runway excursion is a runway safety incident where an aircraft makes an inappropriate exit from the runway. Runway excursions include runway overruns, where an aircraft is unable to stop before it reaches the end of the runway. Runway excursio ...
.
V
1 is defined differently in different jurisdictions, and definitions change over time as aircraft regulations are amended.
*The US
Federal Aviation Administration
The Federal Aviation Administration (FAA) is the largest transportation agency of the U.S. government and regulates all aspects of civil aviation in the country as well as over surrounding international waters. Its powers include air traffic m ...
defines 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. V
1 also means the minimum speed in the takeoff, following a failure of the critical engine at V
EF, at which the pilot can continue the takeoff and achieve the required height above the takeoff surface within the takeoff distance."
V
1 thus includes reaction time.
In addition to this reaction time, a safety margin equivalent to 2 seconds at V
1 is added to the accelerate-stop distance.
*
Transport Canada
Transport Canada (french: Transports Canada) is the department within the Government of Canada responsible for developing regulations, policies and services of road, rail, marine and air transportation in Canada. It is part of the Transportati ...
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."
See also
*
ICAO recommendations on use of the International System of Units
*
Balanced field takeoff
In aviation, a balanced field takeoff is a condition where the takeoff distance required (TODR) with one engine inoperative and the accelerate-stop distance are equal for the aircraft weight, engine thrust, aircraft configuration and runway conditi ...
Notes
References
Further reading
*
{{Flight instruments
Airspeed
Aircraft performance