Airworthiness

Airworthiness is the measure of an aircraft's suitability for safe flight. Certification of airworthiness is conferred by a certificate of airworthiness from the state of aircraft registry national aviation authority, and is maintained by performing the required maintenance actions.

Certification is based on standards applied by national aviation authorities. Interoperability is served when national benchmarks adopt standards from international civil and military organizations such as International Civil Aviation Organization (ICAO), European Aviation Safety Agency (EASA), NATO and European Defence Agency (EDA).

In the U.S., Title 14, Code of Federal Regulations, Subchapter F, Part 91.7 states: "a) No person may operate an aircraft unless it is in an airworthy condition. b) The pilot in command of a civil aircraft is responsible for determining whether that aircraft is in condition for safe flight. The pilot in command shall discontinue the flight when unairworthy mechanical, electrical, or structural conditions occur which compromise the airworthiness."

G-AANG (8087399113)
Blériot XI, civil registration G-AANG. Built in 1909 and operated by the Shuttleworth Collection in the United Kingdom, this is the world's oldest airworthy aircraft

Jurisdictional heterogeneity

One airworthiness regulation is found in ICAO international standard of Annex 8 to Chicago Convention on International Civil Aviation which defines "airworthy" - in respect of an aircraft, engine, propeller or part there of - as "The status of an aircraft, engine, propeller or part when it conforms to its approved design and is in a condition for safe operation". The application of airworthiness defines the condition of an aircraft and its suitability for flight, in that it has been designed with engineering rigor, constructed, maintained and is expected to be operated to approved standards and limitations, by competent and approved individuals, who are acting as members of an approved organization and whose work is both certified as correct and accepted on behalf of the state of aircraft registry.

Apart from this organization, there are other ones like Federal Aviation Administration(FAA) or EASA that establish their own rules. In the case of the FAA, the regulation of airworthiness is found in Title 14 in the collected Code of Federal Regulations. The EASA specifications are found in several regulations: as nº 216/2008 (Basic Regulations), nº 748/2012 (Initial Airworthiness), nº 2015/640 (Adittional specifications about airworthiness) and nº 1321/2014 (Continuing airworthiness).[1]

European Regulation

In the regulation (UE) nº216/2008, is established common rules in the aviation sector and is created the European Aviation Safety Agency. At the article 5 of this regulation appear the first specifications about airworthiness and at the article 20 is about airworthy certification.[2]

The main objective of this rules is to establish and to maintain a high and uniform security level at the civil aviation in Europe. For that reason, It lays down different rules according to the airworthiness:

  • The jets will accomplish the essential established requirements in annex I in airworthy section.
  • It will be proved that the products possess a type certificate.Moreover, it is necessary to include modifications certificate of the same jet,it should be included in supplementary type certificate. Both of them it could be sold when the applicant would have proved that his product achieve the regulations' basis.
  • No airplane can be operated without a valid certificate of airworthiness (C of A)
  • The certificate of airworthiness will be issued when the applicant has demonstrated that the aircraft is conformed to the design of the model approved in its type certificate and that the pertinents documentation, inspections and tests confirm that the aircraft is in a condition for safe use. The certificate of airworthiness shall be valid as long as it is not canceled, or annulled, or is left without effect and provided that the aircraft is kept in accordance with the essential requirements for maintenance of airworthiness.
  • The Commission will ensure, in particular, because the current state of the art and best practices in airworthiness are reflected; that keep in mind the experience accumulated in service by aircraft throughout the world, as well as scientific and technical progress; allow immediate response, once the causes of accidents and serious incidents are determined; do not impose requirements on aircraft that are incompatible with the obligations assumed by the Member States by virtue of their belonging of the International Civil Aviation Organization (ICAO).

Initial airworthiness

The Regulation (EU) No. 748/2012 establishes the dispositions of application on the airworthiness and environmental certification of aircraft and related products, components and equipment, as well as the certification of design and production organizations.[3]

Besides of the technical requirements and common administratives procedures by the airworthiness and environmental certification, the following aspects can be found too in regulation nº 748/2012:

  • The dispatch of type certificates, of restricted type certificates, of supplementary type certificates, as well as the modifications of already said certificates.
  • The dispatch of repairs design approvals.
  • The demonstration that environmental protection requirements are achieved.
  • The dispatch of noise level certificates.
  • The identification and certification of products, components and equipment.
  • The certification of the design and production organizations.
  • The dispatch of airworthiness directives

This regulation contains an annex, Part-21, which specifies the requirements and procedures for the certification of aircraft and related products, components and equipment, and design and production organizations. Apart from this annex, there are also several certification specifications, including CS-25 for large aircraft, and CS-23, for medium and small aircraft.

In application, airworthiness standards include a probability of loss of aircraft (PLOA) that is design controllable (PLOAdc) as an overall attribute.[4] Setting a sufficiently robust PLOA factor for the aircraft's ability to safely attain, sustain, and terminate flight protects the souls on board. An aircraft safe enough to carry human life is presumed safe to fly over people on the ground. For "airworthiness regulations [that] serve to protect people onboard the aircraft . . . the protection of persons and property on the ground [is] another benefit.[5] "

Contrarily for unmanned aircraft, airworthiness must address safety of people on the ground and not the aircraft. This changes the assessment of risks & hazards therefore permitting a new approach to account for risk and consequence in the setting of airworthiness requirements. For military unmanned aircraft, France derived an unmanned-unique airworthiness concept, later adapted by NATO, that isolates failures catastrophic to human life. The concept later came to be described as the "Cumulative Probability of all Catastrophic Failure Conditions" or (PCumCat). Here, two outcomes are addressed.

First an airworthiness issue arises from an uncontrolled crash which is defined as a condition resulting from one or a combination of failure conditions that prevents the flight control system from maintaining the aircraft controllable and maneuverable until the impact on the ground AEP-4671 [6] page A-5. To be certified to overfly all population densities, an uncontrolled crash assumes human life, at the point of impact, is lost.

In the second outcome, a forced landing or recovery at a predefined and unpopulated area is defined as a condition resulting from one or a combination of failure conditions that prevents the UAV from landing on its planned main landing site although the flight control system is still able to maintain the UAV controllable and maneuverable (see AEP-4671, page 1-F-19, U1413 & page A-2). While the aircraft may be lost, residual maneuverability directing to an unpopulated point of impact means this alternative is not catastrophic and therefore not an airworthiness factor. Though the aircraft may be lost or considered a hull loss, the flight has been safely terminated.

Additional airworthiness specifications

The Regulation (EU) nº 2015/640 establishes additional airworthiness specifications for operations and contains two annexes.The Annex I (Part 26), Subpart A, is devoted to general provisions on the appropriate authority, temporarily inoperative equipment and demonstration of conformity. Subpart B of the aforementioned annex focuses on large aircraft and contains specifications related to seats, berths, seat belts and harnesses; location, access and markings of emergency exits; emergency interior lighting and operation of emergency lights; interiors hold; flammability of the coatings of cargo compartments; fire protection for toilets; acoustic warning of the landing gear and systems for opening and closing the flight crew compartment door - incapacitation of a crew member. Annex II contains an amendment to Annex III (part ORO) of Regulation (EU) No. 965/2012.[7]

Continuing airworthiness

The Regulation (EU) No. 1321/2014 controls the continuing of the airworthiness of aircraft and aeronautical products, components and equipment and the approval of the organizations and staff who involve in these tasks. It contains 7 annexes, although Annex V has been repealed. Annex I (Part M); Section A (Technical requirements), "establishes the measures that must be taken to ensure the continuing of airworthiness, including maintenance.Moreover, it specifies the conditions that must be achieved by the people or organizations involved in the management of airworthiness maintenance." Section B (Procedures for the competent authority) "establishes the administrative procedures to be followed by the competent authority for the application and enforcement of Section A of Part M." [8]

The Annex II (Part 145); Section A (Technical requirements), "establishes the requirements which an organization must obey to be able to award or maintain a continuing approval of the elements and aircraft".The Section B (Procedures for Competent Administration) "establishes the administrative procedures that must be followed by the competent authority to execute its tasks and responsibilities in connection with the concession, modification, suspension or revocation of approvals of maintenance organizations Part 145".

The Annex III (Part 66); Section A (Technical requirements), "define the aircraft continuing license and set the requirements for its application, dispatch and continuity of its validity".The Section B (Procedures for the competent authority) "establishes the procedures, requirements, administrative requirements, measurement and control of compliance with Section A of Part 66".

The Annex IV (Part 147); Section A (Technical requirements), "establishes the requirements that must be fulfilled by the organizations that request authorization to carry out training courses and specific examinations in Part 66". Section B (Procedures for competent administration) "establishes the administrative requirements that must be followed by the competent authorities for the application of section A of this part".

The Annex V bis (Part T); Section A (Technical requirements), "establishes the requirements to ensure maintenance of the continuing airworthiness of the aircraft referred to in Article 1, letter b), in accordance with the fundamental requirements set out in Annex IV of the Regulations (EC) No. 216/2008. The conditions to be had by the people and organizations responsible for managing the maintenance of airworthiness and the maintenance of the aircraft in question are also specified".The Section B (Procedures for Competent Authorities) "establishes the administrative procedures that must be followed by the competent authorities in charge of the application and compliance of Section A of Part T".

The Annex VI contains only a table of correspondence between Regulation (EC) No. 2042/2003 and these regulations.

FAA regulations

The USA Federal Aviation Regulations, Part 21, §21.183(d) has a procedural definition of airworthy:
"other aircraft An applicant for a standard airworthiness certificate for aircraft not covered by paragraphs (a) through (c) (a:"New aircraft manufactured under a production certificate." b:"New aircraft manufactured under type certificate only." c:"Import aircraft.") of this section is entitled to a standard airworthiness certificate if -- (1) He presents evidence to the Administrator that the aircraft conforms to a type design approved under a type certificate or a supplemental type certificate and to applicable Airworthiness Directives; (2) The aircraft (except an experimentally certificated aircraft that previously had been issued a different airworthiness certificate under this section) has been inspected in accordance with the performance rules for 100-hour inspections set forth in part 43.15 of this chapter and found airworthy by-- (i)The manufacturer; (ii)The holder of a repair station certificate as provided in part 145 of this chapter; (iii)The holder of a mechanic certificate as authorized in part 65 of this chapter; (v)The holder of a certificate issued under part 121 of this chapter, and having a maintenance and inspection organization appropriate to the aircraft type; and (3)The Administrator finds after inspection, that the aircraft conforms to the type design, and is in condition for safe operation."

An example of an aircraft that was not legally airworthy is the one used in the Lawnchair Larry flight in 1982.

The definition of the term "Airworthy" was never included in the Code of Federal Regulations until the 14 CFR Part 3, General Requirements, was established. The definition was included in the guidance, such as Advisory Circulars and Orders, but never in the Rule. Part 3 defines an Airworthy aircraft as one that conforms to its type design and is in a condition for safe flight.

A more generic and non-process oriented definition of airworthiness is in JSP553 Military Airworthiness Regulations (2006) Edition 1 Change 5:

The ability of an aircraft or other airborne equipment or system to operate without significant hazard to aircrew, ground crew, passengers (where relevant) or to the general public over which such airborne systems are flown

This definition applies equally to civil and military aircraft.[9] An example of a method used to delineate "significant hazard" is a risk reduction technique used by the military and used widely throughout engineering known as ALARP (As Low As Reasonably Practicable). This is defined as:

The principle, used in the application of the Health and Safety at Work Act, that safety should be improved beyond the baseline criteria so far as is reasonably practicable. A risk is ALARP when it has been demonstrated that the cost of any further Risk reduction, where cost includes the loss of capability as well as financial or other resource costs, is grossly disproportionate to the benefit obtained from that Risk reduction.’

In the U.S. Code of Federal Regulations, Title 14, Part 23, § 23.200, states, for the purposes of this part, the following definition applies: "Continued safe flight and landing means an airplane is capable of continued controlled flight and landing, possibly using emergency procedures, without requiring exceptional pilot skill or strength. Upon landing, some airplane damage may occur as a result of a failure condition."

Canadian regulations

In Canada Canadian Aviation Regulations, CAR 101.01, Subpart 1 - Interpretation Content last revised: 2007/12/30
"airworthy" - in respect of an aeronautical product, means in a fit and safe state for flight and in conformity with its type design;

See also

Related subjects

References

  1. ^ "Regulations". EASA. Retrieved 13 May 2018. This article incorporates text from this source, which is in the public domain.
  2. ^ "REGLAMENTO (CE) No 216/2008 DEL PARLAMENTO EUROPEO Y DEL CONSEJO de 20 de febrero de 2008 sobre normas comunes en el ámbito de la aviación civil y por el que se crea una Agencia Europea de Seguridad Aérea, y se deroga la Directiva 91/670/CEE del Consejo, el Reglamento (CE) no 1592/2002 y la Directiva 2004/36/CE (Texto pertinente a efectos del EEE)". 2008R0216 — ES — 29.01.2013 — 003.005 — 1. Retrieved 13 May 2018. This article incorporates text from this source, which is in the public domain.
  3. ^ "REGLAMENTO (UE) No 748/2012 DE LA COMISIÓN de 3 de agosto de 2012 por el que se establecen las disposiciones de aplicación sobre la certificación de aeronavegabilidad y medioambiental de las aeronaves y los productos, componentes y equipos relacionados con ellas, así como sobre la certificación de las organizaciones de diseño y de producción (refundición)". Regulation nº 748/2012. Retrieved 13 May 2018. This article incorporates text from this source, which is in the public domain.
  4. ^ https://eda.europa.eu/docs/default-source/documents/emacc-hdbk-edition-3-0-(1-feb-2018)---endorsed-for-release.pdf
  5. ^ https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20160009270.pdf
  6. ^ AEP-4671 EDB V1 E.(STANAG 4671) 2 Apr 2019
  7. ^ "COMMISSION REGULATION (EU) 2015/640 of 23 April 2015". Retrieved 14 May 2018. This article incorporates text from this source, which is in the public domain.
  8. ^ "Commission Regulation (EU) No 1321/2014 of 26 November 2014". Retrieved 14 May 2018. This article incorporates text from this source, which is in the public domain.
  9. ^ L. Purton & K. Kourousis (2014). "Military Airworthiness Management Frameworks: A Critical Review". Procedia Engineering. 80: 545–564. doi:10.1016/j.proeng.2014.09.111.

External links

Air data inertial reference unit

An air data inertial reference unit (ADIRU) is a key component of the integrated air data inertial reference system (ADIRS), which supplies air data (airspeed, angle of attack and altitude) and inertial reference (position and attitude) information to the pilots' electronic flight instrument system displays as well as other systems on the aircraft such as the engines, autopilot, aircraft flight control system and landing gear systems. An ADIRU acts as a single, fault tolerant source of navigational data for both pilots of an aircraft. It may be complemented by a secondary attitude air data reference unit (SAARU), as in the Boeing 777 design.This device is used on various military aircraft as well as civilian airliners starting with the Airbus A320 and Boeing 777.

Aircraft design

Aircraft design may refer to:

An aircraft design as defined by type definition documentation:

Type certificate, for certified aircraft

Airworthiness certificate, a legal document

Standard Airworthiness Certificate, for certified aircraft

Special Airworthiness Certificate, for non-certified aircraft types

Aircraft design process, the process of creating an individual aircraft design

Aircraft Designs, an aircraft design and manufacturing firm based in Monterey, California, United States

Aircraft design process

The aircraft design process is the engineering design process by which aircraft are designed. These depend on many factors such as customer and manufacturer demand, safety protocols, physical and economic constraints etc. For some types of aircraft the design process is regulated by national airworthiness authorities. This article deals with powered aircraft such as airplanes and helicopter designs.

Aircraft design is a compromise between many competing factors and constraints and accounts for existing designs and market requirements to produce the best aircraft.

Aircraft maintenance

Aircraft maintenance is the performance of tasks required to ensure the continuing airworthiness of an aircraft or aircraft part, including overhaul, inspection, replacement, defect rectification, and the embodiment of modifications, compliance with airworthiness directives and repair.

Airworthiness Directive

An airworthiness directive (commonly abbreviated as AD) is a notification to owners and operators of certified aircraft that a known safety deficiency with a particular model of aircraft, engine, avionics or other system exists and must be corrected.If a certified aircraft has outstanding airworthiness directives that have not been complied with, the aircraft is not considered airworthy. Thus, it is mandatory for an aircraft operator to comply with an AD.

Airworthiness certificate

A standard certificate of airworthiness is a permit for commercial passenger or cargo operation, issued for an aircraft by the national aviation authority in the state/nation in which the aircraft is registered. For other aircraft such as crop-sprayers, a Special Airworthiness Certificate (not for commercial passenger or cargo operations) must be issued.

Centre for Military Airworthiness and Certification

The Centre for Military Airworthiness & Certification (CEMILAC) is a laboratory of the Indian Defence Research and Development Organisation (DRDO). Located in Bangalore, its primary function is certification and qualification of military aircraft and airborne systems. Some of its achievements are issuance of IOC for LCA, ALH.Clearance for Bio-ATF for AN-32. It has 14 regional centres located across the country.

Emergency airworthiness directive

An emergency airworthiness directive (EAD) is an airworthiness directive issued when an unsafe condition exists that requires immediate action by an aircraft owner or operator. EADs are published by a responsible authorities such as FOCA, EASA or FAA related to airworthiness and maintenance of aircraft and aircraft parts. It contains measures which must be accomplished and the related periods to preserve their airworthiness. Technical information is addressed to operators and maintenance organisations of affected aircraft only. EADs become effective upon receipt of notification.

Federal Aviation Administration

The Federal Aviation Administration (FAA) is a governmental body of the United States with powers to regulate all aspects of civil aviation in that nation as well as over its surrounding international waters. Its powers include the construction and operation of airports, air traffic management, the certification of personnel and aircraft, and the protection of U.S. assets during the launch or re-entry of commercial space vehicles. Powers over neighboring international waters were delegated to the FAA by authority of the International Civil Aviation Organization.

Created in August 1958, the FAA replaced the former Civil Aeronautics Administration (CAA) and later became an agency within the U.S. Department of Transportation.

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 are part of Title 14 of the Code of Federal Regulations (CFR). A wide variety of activities are regulated, such as aircraft design and maintenance, typical airline flights, pilot training activities, hot-air ballooning, lighter-than-air aircraft, man-made structure heights, obstruction lighting and marking, and even model rocket launches, model aircraft operation, sUAS & Drone operation, and kite flying. The rules are designed to promote safe aviation, protecting pilots, flight attendants, passengers and the general public from unnecessary risk. Since 1958, these rules have typically been referred to as "FARs", short for Federal Aviation Regulations. However, another set of regulations (Title 48) is titled "Federal Acquisitions Regulations", and this has led to confusion with the use of the acronym "FAR". Therefore, the FAA began to refer to specific regulations by the term "14 CFR part XX".

Joint Aviation Authorities

The Joint Aviation Authorities (JAA) was an associated body of the EASA representing the civil aviation regulatory authorities of a number of European States who had agreed to co-operate in developing and implementing common safety regulatory standards and procedures. It was not a regulatory body, regulation being achieved through the member authorities. It was in existence from 1970 until disbanded in 2009.

In implementing the so-called FUJA Report, the JAA had entered into a new phase as of 1 January 2007. In this new phase the former "JAA" had become "JAA T" (Transition). JAA T consisted of a Liaison Office (JAA LO) and a Training Office (JAA TO). The offices of JAA LO were located in the premises of European Aviation Safety Agency (EASA) in Cologne, Germany.

Joint Aviation Requirements

The Joint Aviation Requirements (JAR) were a set of common comprehensive and detailed aviation requirement issued by the Joint Aviation Authorities, intended to minimise Type Certification problems on joint ventures, and also to facilitate the export and import of aviation products.

They were recognised by the national aviation authorities of participating countries as an acceptable basis for showing compliance with their national airworthiness codes.

The European Aviation Safety Agency (EASA) was created in 2003 and reached full functionality in 2008, and has since taken over most of the JAA functions. JAA Certification Specifications, formerly known as JARs, are recognised by EASA as an acceptable basis for showing compliance with their national airworthiness codes.

Maintenance (technical)

The technical meaning of maintenance involves functional checks, servicing, repairing or replacing of necessary devices, equipment, machinery, building infrastructure, and supporting utilities in industrial, business, governmental, and residential installations. Over time, this has come to include multiple wordings that describe various cost-effective practices to keep equipment operational; these activities take place either before or after a failure.

Together, these functions are referred to as Maintenance, repair and overhaul (MRO). MRO is also used for Maintenance, repair and operations.Over time, the terminology of maintenance and MRO has begun to become standardized. The United States Department of Defense uses the following definitions:

Any activity—such as tests, measurements, replacements, adjustments, and repairs—intended to retain or restore a functional unit in or to a specified state in which the unit can perform its required functions.

All action taken to retain material in a serviceable condition or to restore it to serviceability. It includes inspections, testing, servicing, classification as to serviceability, repair, rebuilding, and reclamation.

All supply and repair action taken to keep a force in condition to carry out its mission.

The routine recurring work required to keep a facility (plant, building, structure, ground facility, utility system, or other real property) in such condition that it may be continuously used, at its original or designed capacity and efficiency for its intended purpose.Maintenance is strictly connected to the utilization stage of the product or technical system, in which the concept of maintainability must be included. In this scenario, maintainability is considered as the ability of an item, under stated conditions of use, to be retained in or restored to a state in which it can perform its required functions, using prescribed procedures and resources.In some domains like aircraft maintenance, terms maintenance, repair and overhaul also include inspection, rebuilding, alteration and the supply of spare parts, accessories, raw materials, adhesives, sealants, coatings and consumables for aircraft maintenance at the utilization stage. In international civil aviation maintenance means:

The performance of tasks required to ensure the continuing airworthiness of an aircraft, including any one or combination of overhaul, inspection, replacement, defect rectification, and the embodiment of a modification or a repair.

This definition covers all activities for which aviation regulations require issuance of a maintenance release document (aircraft certificate of return to service – CRS).

Maximum takeoff weight

The maximum takeoff weight (MTOW) or maximum gross takeoff weight (MGTOW) or maximum takeoff mass (MTOM) of an aircraft is the maximum weight at which the pilot is allowed to attempt to take off, due to structural or other limits. The analogous term for rockets is gross lift-off mass, or GLOW. MTOW is usually specified in units of kilograms or pounds.

MTOW is the heaviest weight at which the aircraft has been shown to meet all the airworthiness requirements applicable to it. MTOW of an aircraft is fixed and does not vary with altitude, air temperature, or the length of the runway to be used for takeoff or landing. A different weight, the "maximum permissible takeoff weight" or "regulated takeoff weight", varies according to flap setting, altitude, air temperature, length of runway and other factors. It is different from one takeoff to the next, but can never be higher than the MTOW.

NATO STANAG 4671

NATO STANAG 4671 is the NATO Standardized Agreement 4671 which is the UAV SYSTEM Airworthiness REQUIREMENTS (USAR). It is intended to allow military Unmanned aerial vehicles (UAVs) to operate in other NATO members airspace.

Page 1 of edition 1 states:If a National Certifying Authority states that a UAV System airworthiness is compliant with STANAG 4671 (and any appropriate national reservations), then, from an airworthiness perspective, that UAV System should have streamlined approval to fly in the airspace of other NATO countries, if those countries have also ratified this STANAG.

Edition 1 was promulgated in September 2009. Edition 2 was promulgated in February 2017.

Draft edition 3 was being commented on (e.g. by the aircraft industry) in Sept 2014, calling attention to slow progress and highlighting concerns. Edition 3 was promulgated in Apr 2019.

National aviation authority

A national aviation authority (NAA) or civil aviation authority is a government statutory authority in each country that maintains an aircraft register and oversees the approval and regulation of civil aviation.

Type certificate

A type certificate signifies the airworthiness of a particular category of aircraft, according to its manufacturing design (‘type’). It confirms that the aircraft is manufactured according to an approved design, and that the design ensures compliance with airworthiness requirements.

For up to three seats, primary category aircraft, certification costs around US$1m, US$25m for a general aviation aircraft and hundreds of millions of dollars for a commercial aircraft; certification delays can cost millions of dollars and can decide a program's profitability.

Ultralight aircraft (United States)

Ultralight aircraft in the United States are much smaller and lighter than ultralight aircraft as defined by all other countries.

In the United States, ultralights are described as "ultralight vehicles" and not as aircraft. They are not required to be registered, nor is the pilot required to have a pilot's certificate.

V speeds

In aviation, V-speeds are standard terms used to define airspeeds important or useful to the operation of all aircraft. These speeds are derived from data obtained by aircraft designers and manufacturers during flight testing for aircraft type-certification testing. Using them is considered a best practice to maximize aviation safety, 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 (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 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. The yellow range is the range in which the aircraft may be operated in smooth air, and then only with caution to avoid abrupt control movement, and 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.

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