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Certification of Aircraft, Design and Production

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Category: Airworthiness Airworthiness
Content source: Cranfield University About Cranfield University
Content control: Cranfield University About Cranfield University
Publication Authority: SKYbrary SKYbrary

Aircraft Certification Requirements

Certification requirements for civil [commercial] aircraft are derived from ICAO Annex 8 Airworthiness of Aircraft [ICAO, 2016] and the ICAO Airworthiness Manual, Part V State of Design and State of Manufacture [ICAO, 2014]. Each ICAO contracting state then establishes its own legal framework to implement the internationally agreed standards and recommended practices.

Procedures for certification of aeronautical products (aircraft, engines and propellers) are published in each state. In the EU, these are contained in EC Regulation 748/2012 Annex I - Part 21 [EC, 2012], whereas in USA they are within FAR Part 21 [FAA, 2017]. These “Part 21” regulations also include procedures for the approval of design organisations (Sub-part J) and production organisations (Sub-part G). These processes are known respectively as Design Organisation Approval (DOA) and Production Organisation Approval (POA).

Such approvals are a necessary pre-requisite to obtaining product certification. The main technical codes to be followed for the design of products for certification are set out below as a list of certification specifications for Europe (EASA) and airworthiness standards for USA (FAA) applicable to different categories of product and environmental consideration.

EASA Title FAA Title
CS-22 Sailplanes and Powered Sailplanes
CS-23 Normal, Utility, Aerobatic and Commuter Aeroplanes Part 23 AIRWORTHINESS STANDARDS: NORMAL, UTILITY, ACROBATIC, AND COMMUTER CATEGORY AIRPLANES
CS-25 Large Aeroplanes Part 25 AIRWORTHINESS STANDARDS: TRANSPORT CATEGORY AIRPLANES
CS-27 Small Rotorcraft Part 27 AIRWORTHINESS STANDARDS: NORMAL CATEGORY ROTORCRAFT
CS-29 Large Rotorcraft Part 29 AIRWORTHINESS STANDARDS: TRANSPORT CATEGORY ROTORCRAFT
CS-31GB CS-31HB (Gas Balloons) (Hot Air Balloons) Part 31 AIRWORTHINESS STANDARDS: MANNED FREE BALLOONS
CS-E Engines Part 33 AIRWORTHINESS STANDARDS: AIRCRAFT ENGINES
CS-P Propellers Part 35 AIRWORTHINESS STANDARDS: PROPELLERS
CS-LSA Light Sport Aeroplanes
CS-VLA Very Light Aeroplanes
CS-VLR Very Light Rotorcraft
CS-34 Aircraft Engine Emissions and Fuel Venting Part 34 FUEL VENTING AND EXHAUST EMISSION REQUIREMENTS FOR TURBINE ENGINE POWERED AIRPLANES
CS-36 Aircraft Noise Part 36 NOISE STANDARDS: AIRCRFAT TYPE AND AIRWORTHINESS CERTIFICATION

For full details of EASA Certification Specifications see the EASA Agency rules (Soft law) [EASA, 2017]. Full details of FAA Standards are also available [FAA, 2017].

Compliance with these specifications or standards is approached in one of two ways depending on the requirement. For structures typically the approach is known as Deterministic whereas for systems, a Probabilistic approach is taken. One example of each approach would be:

  • For structure - No detrimental deformation of the airframe under the loads produced by a given magnitude of manoeuvre.
  • For systems - Any catastrophic failure condition must (i) be extremely improbable [1 in 109 flight hours]; and (ii) must not result from a single failure.

For the safety assessment of aircraft systems, regulations are given in EASA CS25.1309 [EASA, 2016] and FAA Aviation Rulemaking Advisory Committee draft AC25.1309-1B [FAA, 2002]. Useful guidelines for conducting the safety assessment process are also given in ARP4761 [SAE, 1996].

Type-certification Process

The process for civil aircraft by which type certification is achieved comprises four steps. These are outlined below, but additional details can be found from EASA (2010), Type certification [EASA, 2010] and FAA Order 8110.4C [FAA, 2011]

1. Technical Overview and Certification Basis The product designer presents the project to the primary certificating authority (PCA) - EASA in EU, FAA in USA - when it is sufficiently mature. The certification team and the set of rules (Certification Basis) that will apply for the certification of this specific product type are established. In principal this agreed certification basis remains unchanged for a period of five years for an aircraft, three years for an engine.

2. Certification Programme The PCA and the designer define and agree on the means to demonstrate compliance of the product type with every requirement of the Certification Basis. Also at this stage the level of regulatory involvement is proposed and agreed.

3. Compliance demonstration The designer has to demonstrate compliance of the aircraft with regulatory requirements: for all elements of the product e.g. the airframe, systems, engines, flying qualities and performance. Compliance demonstration is done by analysis combined with ground and flight testing. The PCA will perform a detailed examination of this compliance demonstration, by means of selected document reviews and test witnessing.

4. Technical closure and Type Certificate issue When technically satisfied with the compliance demonstration by the designer, the PCA closes the investigation and issues a Type certificate. For European-designed aircraft, EASA delivers the primary certification which is subsequently validated by other authorities for registration and operation in their own countries, e.g. the FAA for the USA. Similarly EASA will validate the FAA certification of US-designed aircraft. This validation is carried out under a Bilateral Aviation Safety Agreement (BASA) between the states concerned.

Notes:

a. A Type Certificate applies to an aircraft (engine or propeller) of a particular Type Design. Every individual aircraft of that type has to gain its own Certificate of Airworthiness C of A which is achieved when it can be shown to conform to the certificated Type Design and is in a condition for safe operation. As a general rule civil aircraft are not allowed to fly unless they have a valid C of A.

b. Organisation approvals, issued under Part 21, are based on regulatory assessment of capability, facilities, manpower, resources and quality assurance systems in relation to the tasks undertaken. Helpful supporting standards in this respect are AS/EN 9100 and AS/EN9120B [SAE, 2016].

c. Certification of military aircraft has in the past not followed the typical Type Certification Process outlined above. However since 2010 in Europe a very similar process has been evolved by the European Defence Agency (EDA). Known as the Military Airworthiness Authorities (MAWA) Forum [EDA, 2017], one of the documents published is a military guide to certification, denoted EMAR21 [EDA, 2016]. The documents are issued as requirements and do not have legal standing but are nevertheless being followed by a number of states both within and outside Europe.

Accidents and Incidents

There follows a sample of extracts from reports held on SKYbrary that involve a design issue as a contributory factor in the accident:

  • A321, en-route, near Pamplona Spain, 2014 (On 5 November 2014, the crew of an Airbus A321 temporarily lost control of their aircraft in the cruise and were unable to regain it until 4000 feet of altitude had been lost. An investigation into the causes is continuing but it is already known that blockage of more than one AOA probe resulted in unwanted activation of high AOA protection which could not be stopped by normal sidestick inputs until two of the three ADRs had been intentionally deactivated in order to put the flight control system into Alternate Law.)
  • B38M, en-route south east of Addis Ababa Ethiopia, 2019 (On 10 March 2019, the left angle of attack vane of a Boeing 737-MAX 8 began recording erroneous values shortly after takeoff from Addis Ababa which triggered left stick shaker activation which continued for the remainder of the flight. Immediately after flap retraction was complete, a series of automatic nose down stabiliser trim inputs began, which the pilots were eventually unable to counter after which a high speed dive led to terrain impact six minutes after takeoff. The Investigation is continuing.)
  • B752, Jackson Hole WY USA, 2010 (On 29 December 2010 an American Airlines Boeing 757-200 overran the landing runway at Jackson Hole WY after a bounced touchdown following which neither the speed brakes nor the thrust reversers functioned as expected. The subsequent investigation found that although the speed brakes had been armed and the ‘deployed’ call had been made, this had not occurred and that the thrust reversers had locked on transit after premature selection during the bounce. It was noted that had the spoilers been manually selected, the thrust reverser problem would not have prevented the aircraft stopping on the runway.)
  • A140, vicinity Tehran Mehrabad Iran, 2014 (On 10 August 2014, one of the engines of an Antonov 140-100 departing Tehran Mehrabad ran down after V1 and prior to rotation. The takeoff was continued but the crew were unable to keep control and the aircraft stalled and crashed into terrain near the airport. The Investigation found that a faulty engine control unit had temporarily malfunctioned and that having taken off with an inappropriate flap setting, the crew had attempted an initial climb with a heavy aircraft without the failed engine propeller initially being feathered, with the gear remaining down and with the airspeed below V2.)
  • MD11, en-route, Atlantic Ocean near Halifax Canada, 1998 (On 2 September 1998, an MD-11 aircraft belonging to Swissair, crashed into the sea off Nova Scotia following an in-flight electrical fire.)
  • DC10, en-route, Paris France, 1974 (On 3 March 1974, all 346 occupants were killed when a Turkish Airlines McDonnell Douglas DC 10 suffered an explosive decompression after an improperly secured hold door detached passing 12000ft in the climb shortly after departing Paris Orly. It was found that non-mandated corrective actions promulgated after the investigation into a similar DC10 explosive decompression in Canada nearly two years earlier had identified an identical fault in the door closure mechanism which had allowed it to indicate and appear secured when it was not had not been completed on the aircraft at the time of the accident.)

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