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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.)
  • CONC, vicinity Paris Charles de Gaulle France, 2000 (On 25th July 2000, an Air France Concorde crashed shortly after take-off from Paris CDG following loss of control after debris from an explosive tyre failure between V1 and VR attributed to runway FOD ruptured a fuel tank and led to a fuel-fed fire which quickly resulted in loss of engine thrust and structural damage which made the aircraft impossible to fly. It was found that nothing the crew failed to do, including rejecting the take off after V1 could have prevented the loss of the aircraft and that they had been faced with entirely unforeseen circumstances.)
  • 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.)
  • 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.)
  • B733, vicinity Pittsburg PA USA, 1994 (On 8 September 1994, a US Air Boeing 737-300 crashed near Pittsburg USA following loss of control attributed to a rudder malfunction.)
  • EC25, en-route, 20nm east of Aberdeen UK, 2012 (On 10 May 2012, the crew of a Eurocopter EC225 LP on a flight from Aberdeen to an offshore platform received an indication that the main gearbox (MGB) lubrication system had failed. Shortly after selecting the emergency lubrication system, that also indicated failure and the crew responded in accordance with the QRH drill to “land immediately” by carrying out a successful controlled ditching. The ongoing investigation has found that there had been a mechanical failure of the MGB but that the emergency lubrication system had, contrary to indications, been functioning normally.)

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