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Certification of Aircraft, Design and Production
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|Content source:||Cranfield University|
|Content control:||Cranfield University|
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.
|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:
- B772, en-route Bozeman MT USA, 2008 (On 26 November 2008, a Boeing 777-200 powered by RR RB211 Trent 800 series engines and being operated by Delta AL on a scheduled passenger flight from Shanghai Pudong to Atlanta was in the cruise at FL390 in day VMC in the vicinity of Bozeman MT when there was an uncommanded thrust reduction or ‘rollback’ of the right engine.)
- LJ60, Columbia SC USA, 2008 (On September 19 2008, a Learjet 60 departing Columbia SC USA on a non scheduled passenger overran after attempting a rejected take off from above V1 and then hit obstructions which led to its destruction by fire and the death or serious injury of all six occupants. The subsequent investigation found that the tyre failure which led to the rejected take off decision had been due to under inflation and had damaged a sensor which caused the thrust reversers to return to their stowed position after deployment with the unintended forward thrust contributing to the severity of the overrun.)
- DH8D, Saarbrucken Germany, 2015 (On 30 September 2015, the First Officer on an in-service airline-operated Bombardier DHC-8 400 selected the gear up without warning as the Captain was in the process of rotating the aircraft for take-off. The aircraft settled back on the runway wheels up and eventually stopped near the end of the 1,990 metre-long runway having sustained severe damage. The Investigation noted that a factor contributing to the First Officer's unintended action may have been her "reduced concentration level" but also highlighted the fact that the landing gear control design logic allowed retraction with the nose landing gear airborne.)
- B772, Singapore, 2010 (On 14 June 2010, a Boeing 777-200 being operated by British Airways on a scheduled passenger service from Singapore to London Heathrow with a relief crew present on the flight received indications of abnormal functioning of the right engine during a night take off in VMC. Subsequent and directly related developments en route, including greater than planned fuel consumption which put the intended destination out of reach, led to the declaration of a PAN to ATC and diversion to Amsterdam. Inspection after flight found that parts of the right engine were damaged or missing and the latter were matched to previously unidentified debris recovered from the runway at Singapore. None of the 214 occupants were injured.)
- SW4, Mirabel Montreal Canada, 1998 (On 18 June 1998, the crew of a Swearingen SA226 did not associate directional control difficulty and an extended take off ground run at Montreal with a malfunctioning brake unit. Subsequent evidence of hydraulic problems prompted a decision to return but when evidence of control difficulties and fire in the left engine followed, a single engine diversion to Mirabel was flown where, just before touchdown, the left wing failed upwards. All occupants were killed when the aircraft crashed inverted. The Investigation found that overheated brakes had caused an engine nacelle fire which spread and eventually caused the wing failure.)
- B732, Manchester UK, 1985 (On 22nd August 1985, a B737-200 being operated by British Airtours, a wholly-owned subsidiary of British Airways, suffered an uncontained engine failure, with consequent damage from ejected debris enabling the initiation of a fuel-fed fire which spread to the fuselage during the rejected take off and continued to be fuel-fed after the aircraft stopped, leading to rapid destruction of the aircraft before many of the occupants had evacuated.)
- 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 (external links)
- EASA (2010), Type certification, PR.TC.00001-002 (external link)
- 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. (external link)
- 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. (external link)
- 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 (external link)
- FAA, FAA Standards
- FAA, FAR Part 21 - Certification Procedures for Products and Articles (external link)
- FAA (2002), AC25.1309-1B System Design and Analysis, Draft Arsenal edition. (external link)
- 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