Certification of Aircraft, Design and Production
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|Content source:||Cranfield University|
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Aircraft Certification Requirements
Certification requirements for civil [commercial] aircraft are derived from International Civil Aviation Organisation (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.
|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].
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.
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:
- AT76, vicinity Taipei Songshan Taiwan, 2015 (On 4 February 2015, a TransAsia Airways ATR 72-600 crashed into the Keelung River in central Taipei shortly after taking off from nearby Songshan Airport after the crew mishandled a fault on one engine by shutting down the other in error. They did not realise this until recovery from loss of control due to a stall was no longer possible. The Investigation found that the initial engine fault occurred before getting airborne and should have led to a low-speed rejected take-off. Failure to follow SOPs and deficiencies in those procedures were identified as causal.)
- B788, en-route Shikoku Island Japan, 2013 (On 16 January 2013, a main battery failure alert message accompanied by a burning smell in the flight deck was annunciated as an ANA Boeing 787-8 climbed through FL320 on a domestic flight. A diversion was immediately initiated and an emergency declared. A landing at Takamatsu was made 20 minutes later and an emergency evacuation completed. The Investigation found that the battery had been destroyed when thermal runway followed a suspected internal short circuit in one of the battery cells and concluded that certification had underestimated the potential consequences of such a single cell failure.)
- E170 / F900, en-route, east of Varna Bulgaria, 2015 (On 30 June 2015 the crew of an en route Embraer 170 failed to notice that their transponder had reverted to Standby and the ATC response, which involved cross border coordination, was so slow that the aircraft was not informed of the loss of its transponder signal for over 30 minutes by which time it had already passed within 0.9nm of an unseen Dassault Falcon 900 at the same level. The Investigation found that the Embraer crew had failed to follow appropriate procedures and that the subsequent collision risk had been significantly worsened by a muddled and inappropriate ATC response.)
- AT75, en-route, north of Visby Sweden, 2014 (On 30 November 2014, an ATR 72-500 suddenly experienced severe propeller vibrations whilst descending through approximately 7,000 feet with the power levers at flight idle. The vibrations "subsided" after the crew feathered the right engine propeller and then shut the right engine down. The flight was completed without further event. Severe damage to the right propeller mechanism was found with significant consequential damage to the engine. Several other similar events were found to have occurred to other ATR72 aircraft and, since the Investigation could not determine the cause, the EASA was recommended to impose temporary operating limitations pending OEM resolution.)
- GLF4, Bedford MA USA, 2014 (On 31 May 2014, a Gulfstream IV attempted to take off with the flight control gust locks engaged and, when unable to rotate, delayed initiating the inevitable rejected take off to a point where an overrun at high speed was inevitable. The aircraft was destroyed by a combination of impact forces and fire and all seven occupants died. The Investigation attributed the accident to the way the crew were found to have habitually operated but noted that type certification had been granted despite the aircraft not having met requirements which would have generated an earlier gust lock status warning.)
- F50, vicinity Luxembourg, 2002 (On 6 November 2002, a Fokker 50 operated by Luxair, crashed on approach to Luxembourg Airport following loss of control attributed to intentional operation of power levers in the ground range, contrary to SOPs.)
- Accident and Serious Incident Reports: AW - a list of reports concerning events where airworthiness was a causal or contributory factor.
- De Florio F (2016), Airworthiness: An Introduction to Aircraft Certification, 3rd edition, Butterworth-Heinemann
- EASA (2016), Certification Specifications and Acceptable Means of Compliance for Large Aeroplanes CS-25, Amendment 18.
- EASA (2010), Type certification, PR.TC.00001-002
- EASA (2017) Agency rules (Soft law), Certification Specifications
- EC (2012), Commission regulation (EU) No 748/2012, laying down implementing rules for the airworthiness and environmental certification of aircraft and related products, parts and appliances, as well as for the certification of design and production organisations.
- EC (2014), Commission regulation (EU) No 1321/2014 on the continuing airworthiness of aircraft and aeronautical products, parts and appliances, and on the approval of organisations and personnel involved in these tasks.
- EDA (2017) Military Airworthiness Authorities (MAWA) Forum
- EDA (2016), EMAR 21 - Certification of Military Aircraft and Related Products, Parts and Appliances, and Design and Production Organisations, Edition 1.2
- FAA (2011), Type Certification, Order 8110.4C
- FAA, FAA Standards
- FAA, FAR Part 21 - Certification Procedures for Products and Articles
- FAA (2002), AC25.1309-1B System Design and Analysis, Draft Arsenal edition.
- ICAO (2016), Annex 8 Airworthiness of Aircraft, 11th Edition, ICAO
- ICAO (2014), Doc 9760 Airworthiness Manual, Part V. State of Design and State of Manufacture, 3rd Edition, ICAO.
- SAE International (1996), ARP 4761 Guidelines and Methods for conducting the safety assessment process on civil airborne systems and equipment, SAE (1996)
- SAE International (2016), AS/EN9100D, Quality Management Systems - Requirements for Aviation, Space, and Defence Organisations
- SAE International (2016), AS/EN9120B Quality Management Systems – Requirements for Aviation, Space, and Defence Distributors