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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:
- B744, Johannesburg South Africa, 2009 (On 11 May 2009, a British Airways Boeing 747-400 departing Johannesburg came close to stalling following a stall protection system activation during night rotation which continued until landing gear retraction despite immediate appropriate crew response. Subsequent investigation found that loss of lift on rotation had resulted from the unanticipated effect of a design modification in respect of thrust reverser unlocked signals with the aircraft in ‘ground’ status. The Investigation found that the potential effects of this on the transition from ‘ground’ to ‘air’ status including the lower stalling angle of attack in ground effect had not been foreseen.)
- 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.)
- A388, en-route, northern Afghanistan, 2014 (On 5 January 2014, an Airbus A380-800 en route to Singapore at night made an emergency descent and diversion to Baku after a loss of cabin pressure without further event. The Investigation attributed the pressure loss to a fatigue crack in a door skin which was initiated due to a design issue with door Cover Plates, which had not been detected when the Cover Plate was replaced with an improved one eighteen months earlier. Safety Issues related to cabin crew use of emergency oxygen and diversions to aerodromes with a fire category less than that normally required were also identified.)
- AT72, en-route, Mediterranean Sea near Palermo Italy, 2005 (On 6 August 2005, a Tuninter ATR 72-210 was ditched near Palermo after fuel was unexpectedly exhausted en route. The aircraft broke into three sections on impact and 16 of the 39 occupants died. The Investigation found that insufficient fuel had been loaded prior to flight because the flight crew relied exclusively upon the fuel quantity gauges which had been fitted incorrectly by maintenance personnel. It was also found that the pilots had not fully followed appropriate procedures after the engine run down and that if they had, it was at least possible that a ditching could have been avoided.)
- B744, en-route NNW of Bangkok Thailand, 2008 (On 7 January 2008, a Boeing 747-400 being operated by Qantas on a scheduled passenger flight from London Heathrow to Bangkok was descending through FL100 about 13.5 nm NNW of destination in day VMC when indications of progressive electrical systems failure began to be annunciated. As the aircraft neared the end of the radar downwind leg, only the AC4 bus bar was providing AC power and the aircraft main battery was indicating discharge. A manual approach to a normal landing was subsequently accomplished and the aircraft taxied to the designated gate where passenger disembarkation took place. None of the 365 occupants, who included two heavy crew members who were present in the flight deck throughout the incident, had sustained any injury and the aircraft was undamaged.)
- B788, Boston MA USA, 2013 (On 7 January 2013, a battery fire on a Japan Air Lines Boeing 787-8 began almost immediately after passengers and crew had left the aircraft after its arrival at Boston on a scheduled passenger flight from Tokyo Narita. The primary structure of the aircraft was undamaged. Investigation found that an internal short circuit within a cell of the APU lithium-ion battery had led to uncontained thermal runaway in the battery leading to the release of smoke and fire. The origin of the malfunction was attributed to system design deficiency and the failure of the type certification process to detect this.)
- 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