Certification of Aircraft, Design and Production

Certification of Aircraft, Design and Production

Article Information
Category:
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 and the ICAO Airworthiness Manual, Part V State of Design and State of Manufacture. 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, whereas in USA they are within FAR Part 21. 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 prerequisite 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). Full details of FAA Standards are also available.

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 x 10-9 per flight hour]; and (ii) must not result from a single failure.

For the safety assessment of aircraft systems, regulations are given in EASA CS25.1309 and FAA Aviation Rulemaking Advisory Committee draft AC25.1309-1B. Useful guidelines for conducting the safety assessment process are also given in ARP4761.

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 and FAA Order 8110.4C

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.

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, one of the documents published is a military guide to certification, denoted EMAR21. The documents are issued as requirements and do not have legal standing, but are nevertheless 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:

B738, Bristol UK, 2024

On 4 March 2024, a Boeing 737-800 departing Bristol took longer than expected to become airborne and passed over the end of the runway at approximately 10 feet. It was then initially unable to climb at a speed much above V2 until it was recognised that the thrust set was significantly below that intended. Despite the flight being used for new captain line training, a check at 80 knots that correct thrust was set did not occur. The fact that the autothrottle had not been successfully re-engaged after it dropped out when takeoff thrust was being set went unrecognised.

B738, vicinity Billund, Denmark, 2023

On 21 December 2023, a Boeing 737-800 experienced a flap load protection response to turbulence during a night go-around at Billund, which locked the flaps in a mid-range position. A diversion to Copenhagen was commenced, but when it became clear that the fault would result in landing with slightly below minimum reserve fuel, a MAYDAY was declared. The flight was completed without further event. It was concluded that flap system locking had probably resulted from the crew’s manual selection of 15° flap just as the flap load relief system was responding, as designed, to a turbulence-caused flap overspeed condition.

A332, northwest of Phuket, Thailand, 2012

On 20 December 2012, a PW4168A-engined Airbus A330-200 was climbing through FL220 after departing Phuket, Thailand, at night when sudden uncontained left engine failure occurred. Engine shutdown and initiation of a return was followed by loss of the green and then blue hydraulic systems. Shortly after this, a relatively uneventful landing followed with only minor damage but “without pilot assessment or knowledge of the safety margin." As the findings of the investigation raised still-relevant concerns about the way this multiple-failure scenario was handled, it was felt useful to publish the 148-page final report eleven years later.

B763, en-route, Galicia Spain, 2022

On 8 February 2022, a Boeing 767-300ER inbound to Madrid at FL340 experienced a failure of automatic pressurisation control, followed almost three hours later by a failure of manual control and rapidly rising cabin altitude. An emergency was declared and descent made to FL120 where manual control was regained. The flight was completed without recurrence. The failure cause was found to have been water leaking from a tube with a broken clamp which, when it froze, had blocked the air conditioning outflow valve doors. Elements of the system design, scheduled maintenance requirements, and fault detection were identified as contributing factors.

A320, Copenhagen Denmark, 2022

On 8 April 2022, an Airbus A320 made a multiple-bounce touchdown at Copenhagen followed by thrust reverser deployment. The captain rejected the landing and began a go-around, but as the left main gear had bounced and was not on the ground when thrust was set, the left engine reverser did not stow. Full aircraft control was briefly lost and a runway excursion narrowly avoided before a recovery to a single engine MAYDAY circuit and landing followed. Engine software design prevented thrust reverser stowage without weight on wheels, which was why rejected landings after reverser deployment were prohibited.

...further results

Further Reading

Categories
Airworthiness, Certification, Enhancing Safety

Related Articles

SKYbrary Partners:

Safety knowledge contributed by: