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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:

  • B734, en-route, east northeast of Tanegashima Japan, 2015 (On 30 June 2015, both bleed air supplies on a Boeing 737-400 at FL370 failed in quick succession resulting in the loss of all pressurisation and, after making an emergency descent to 10,000 feet QNH, the flight was continued to the planned destination, Kansai. The Investigation found that both systems failed due to malfunctioning pre-cooler control valves and that these malfunctions were due to a previously identified risk of premature deterioration in service which had been addressed by an optional but “recommended” Service Bulletin which had not been taken up by the operator of the aircraft involved.)
  • 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.)
  • 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.)
  • 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.)
  • 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.)
  • MD82, Madrid Barajas Spain, 2008 (On 20 August 2008, an MD82 aircraft operated by Spanair took off from Madrid Barajas Airport with flaps and slats retracted; the incorrect configuration resulted in loss of control, collision with the ground, and the destruction of the aircraft.)

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