Aircraft design process involved in varied disciplines such as aerodynamics, structures, flight mechanics etc. Therefore, for an aircraft to become operational it is essential to demonstrate that the construction and design of the aircraft can comply with the requirements applicable and such verification and validation evidence required to be delegated to the relevant authorities.
This report introduces ‘Airworthiness’ and provides the reader the framework involved in gaining airworthiness and how to maintain it subsequently.
Consideration of airworthiness policies has its origins since the early days of military flying. But aircraft design data has been recorded prior to 1910 for balloons and the Royal Aircraft Factory has produced a design requirement document in 1916. The Aerial Navigation Act that is sanction by the Home Office in 1911 to ban flying in populated areas is an early example of safety regulation.
Airworthiness Department has been established decade later by the Royal Aircraft Factory (as part of the Air Ministry), which is the beginning of procedures for company design approvals and approved data.
Aircraft airworthiness means compliance with applicable aviation authorities regulations that defines the minimum safety level of the aircraft, of the passengers transported and the over flown territories.
When designed and built according to applicable requirements’,
When operated within its’ intended environment and within its’ quantified and declared limitations,
And maintained in accordance with procedures acceptable to the responsible Authority.
The European Aviation Safety Agency (EASA) Regulation 216/2008, Article 5, 2(c) defines the airworthiness as;
“Each aircraft shall be issued with an individual certificate of airworthiness when it is shown that it conforms to the type design approved in its type-certificate and that relevant documentation, inspections and tests demonstrate the aircraft is in condition for safe operation”
The Airworthiness is a collective responsibility of operators, authorities, manufactures and maintenance organisations. An airworthy aircraft is one where the likelihood of any incident or accident as a result of malfunction, performance or handling of the aircraft is kept to acceptable levels. The only real measure of airworthiness in use is given by tracking and analyzing incidents and accidents. The remaining sections will discuss the essence of “Gaining and Maintaining Airworthiness”.
Figure 01: Airworthiness – Collective Responsibilities
Implementation of Airworthiness
Authority (EASA) confidence that the design of a product complies with the applicable requirements based on Certification of the organisation (IR 21 – DOA) & Certification of the design of products (CS 25 – TC)
According to European Aviation Safety Agency (EASA), Design Organisation Approval (DOA) requirements Implementing Rule (IR) part 21 (published as annex to European Commission Regulation (EC) No 1702/2003) includes procedural requirements applicable either to the industry (Section A) or to the Competent Authorities (Section B) but Part 21 does not include provisions to delegate EASA authority and / or signature to individuals.
“Certification of aircraft and related products, parts and appliances, and of design and production organisations”
Organisations must demonstrate following key elements in order to obtain DO Approval.
Design Assurance System
Terms of Approval
Obligations of the holder
Figure 02 – DOA Key Elements
Design Organisation Approval (DOA) – Organisation Structure
Following diagram illustrates a simplified organisation structure demonstrating the essential elements in an aircraft design and manufacturing organisation.
Figure 03: Design Organisation Structure
Chief Executive Officer (CEO):
Responsible for appropriate functioning of the work place by ensuring availability of required resources.
Designated Certification Specialist (DCS):
Airworthiness specialist nominated for a given discipline (ATA or Sub-ATA level or for Approved Manuals) to carry out the certification tasks, in particular to manage the compliance demonstration activities for their domain.
Part of the airworthiness function and act under the control of Product Integrity.
Certification Manager (CM)
Certification panel leaders for their area of competence,
Participate in the development of new certification strategies
The CM is the interface with Aviation Authorities at panel level for primary TC, foreign certification / validation activities and for allocated major changes.
Chief Airworthiness Engineer (CAE)
Responsible for leading and coordinating the certification and airworthiness activities for the programme.
Supported by a team usually called the CAE team composed of:
A Type Certification Manger (TCM)
An Individual Aircraft Certification Manager (IACM)
A Continued Airworthiness Manager (CAM)
Type certification is the process demonstrating that the design of an aircraft complies with the applicable aviation requirements. Certification process could be a new type certificate new aircraft (ex. Airbus A380), Amended Type certification model or derivative (ex: Airbus A350 – 1000) and significant major changes to the type design (ex. A330-200 Passenger to Freighter)
To grant and EASA Type Certificate, aircraft manufacture shall obtain first a DOA (Design Organisation Approval) covering the relevant product (aircraft type) and also shall demonstrate its capability to design, certify and ensure the continued airworthiness of its products in accordance with the certification specification (CS-25) and Environmental protection (CS-34, CS-36) requirements.
To manufacture and release to service series aircraft, manufacture must then obtain a POA (Production Organisation Approval) and establish relationship between DOA & POA.
Flight testing process could be potentially very risky and extremely expensive due to unforeseen problem s result in loss of life (both crew and people on the ground) and damage to the aircraft. Due to this reasons modern flight testing is one of the most safety conscious operations. Typically there are two types of flight test programs, military and commercial. There is a significant difference between military and commercial flight testing where commercial test programs are carried out to certify the aircraft meets all required safety and performance requirements where as military programs involved in aircraft manufactures designing and building aircraft to government contracts to meet specific mission capabilities. Initiation of flight test preparations for both commercial and military aircraft commence well before the aircraft is ready to fly, although due to the fact that the government is funding the military projects, involvement of military flight testing is commence much early-on in the design and testing process.
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Historical Data Analysis
According to historical evidence, operational and airframe related risk of a serious accident causes is approximately one per million flight hours but failure problems occurred by aircraft systems problems is about 10 percent of this total amount. Therefore, it is reasonable to argue that systems faults should not allowed serious accidents and it is therefore possible for a new design to change the probability of such a serious accident not to be greater than one per ten million flight hours (1 x 10-7).
But it is not possible to identify whether the target can be met until all the aircraft systems has been numerically collectively analysed. Due to this reason it’s assumed that there are about 100 potential failure conditions present arbitrarily which could prevent safe flight and landing of the aircraft. By sharing out equally the target allowable risk (x 10-7) equally among these conditions risk allocation result in not greater than 1 x 10-9 to each. Therefore the upper risk limit for failure conditions would be 1 x 10-9 for each hour of flight which approximates probability value for the term “Extremely Improbable”.
Various analytical techniques have been developed in line with the above topic to assist Airworthiness Authority and the applicant to carry out a safety analysis, which could benefit systematic qualitative analysis. This technique also important for analyst to perform quantitative assessment when required.
The Advisory Material Joint (AMJ) identifies both qualitative and quantitative analytical approaches which could used to support JAA personal or assist applicant to determine the compliance with the requirement. And it also provides guidance for determining if or when a particular analysis to be conducted. The intended requirement of the analytical tools is supplement but not to replace operational and engineering judgement.
To have a basic understanding of the legal requirement is vital for aviation professionals such as pilots, mechanics, air traffic controllers and executives. National and international laws or regulations regulate all aspects of civil air transportation. To ensure the effectiveness of the legal framework and enforceability of safety aspects, the following basic groups of regulations have been developed.
Airworthiness Regulations to define:
Applicable procedures, and
Minimum safety, technical and performance requirements to be realised and maintain in the aircraft design.
Ex: EASA Part 21 (aircraft certification procedures), Part M and Part 145 (aircraft maintenance) & CS-25 (design code for large aircraft)
Operational regulations: to define the basic rules air traffic has to follow and the minimum requirements for certain kinds of operations, for the aircraft and the person or the organisation.
Ex: EU-OPS1 Commercial Air Transportation
After an accident there is two main investigations (technical & legal proceedings) will be conducted. Legal proceedings consist with;
Civil proceedings which involved in civil claims for damages by victims and/or their relatives, Commercial proceedings which involved in claims for damages by customer and/or its insurer (Aircraft repair / loss, Reduction in aircraft residual value, Loss of revenue) and finally Criminal prosecution, in case of death / serious injury, in certain jurisdictions (ex: France, Germany).
According to ICAO Doc No 9760-2001 continued Airworthiness defined as ‘The processes that ensure, at any time in its life, an aircraft complies with the technical conditions fixed to the issue of the Certificate of Airworthiness and is in a condition for safe operation.’ And recommends ‘Contracting states are required to have a system that ensures aircraft are in a condition for safe operation.’
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F. Florio (2006) stated that safety is the most important thing which has to be ensuring every time in every flight operations and all the airplanes must be in an air worthy state which is suitable for fly. In other words all the aircrafts must achieve and perform all the procedures in the Airworthiness Directive manuals. Furthermore, Florio (2006) also mentioned that continued airworthiness can be rely on two factors
Maintenance can be explained as alterations, inspections, replacements of parts of the aircraft. This can be done by taking a record entry for each event such as replacement of LRUs (Line replacement units).
According to Florio (2006), Maintenance refers to as ‘preventive maintenance, alterations and repairs and introduction of airworthiness directive’ and also he stated that airworthiness is rely on the maintenance programmes , which also establish the replacement of time change items , the overhaul engines, propellers and various parts of appliances.
Florio mentioned that as the part of the product type certifications of aircraft airworthiness authorities requires instructions for continued airworthiness thus these instructions can be identified as the fundamental tools of the maintenance because they are the basic maintenance programmes. These maintenance programmes must cater the requirements of operational and maintenance standards.
According to EASA Maintenance programme;
Every aircraft shall be maintained in accordance with the maintenance programmes approved by the competent authority, which shall be periodically reviewed and amended accordingly.
The maintenance programme and any subsequent amendments shall be approved by the competent authority
The maintenance programmes must establish compliance with;
Instructions for continuing airworthiness issued by the type certificate and the supplementary type certificate holder
Instructions issued by the complement authority
Instructions issued by the owner or the operator and approved by the competent authority.
Repair process involves different organisations where, when the products are not with aircraft manufacture, continuing airworthiness is governed by the state of registry or the responsibilities are spread out in organisations.
Part 21A subpart M states the repair procedural requirements for certification.
Under Part 21 subpart M:
Elimination of damage (21A.431 b)
Unrepaired damages (21A.445 a)
Out of Part 21 subpart M
Replacement without design activity (21A.431c)
Repairs design from an approved manual (GM 21A.431 a)
Following diagrams illustrates the Airbus repairing process.
Figure 04: Airbus Repairing Process
The Structure Repair Manual (SRM) describes general repair practices, materials and typical repairs, allowed damages, which are considered applicable to standard repairs. It’s approved by aircraft manufacture under DOR privilege.
Changes made to a particular aircraft after the issue of the airworthiness certificate is a modification. This could include changes to the structures, systems, powerplants, propellers etc… Furthermore, substitution of one type for another also considered as a modification. Any modification requires approval from the Civil Aviation Authority directly or via an approved organisation.
During a design modification, details of the change must be given to the authority at early stage where then the modification is classified as minor or major medication according to the nature of the investigation. If the outcome of an investigation requires amendments to the Certificate of Airworthiness or Flight Manual, authority may require following major modification procedures.
Incidents and Accidents
Flight safety experts believe that series of events leads to incidents and accidents.
Accidents – During the operation of an aircraft, result in occurrence associated with a person being fatally or seriously injured from the time any person boards to the aircraft with intention of flight until the time all persons disembarked.
Incidents – Other than accidents incidents also occurrences which relate to the operation of the aircraft or could affect the safety of its operation.
Civil Aviation authority has defined Aging aircrafts as ‘An operational aircraft approaching the end of its design life assumptions’ (Alder P. 2005). Aging aircraft can also be called as an older aircraft as well. Since the aircraft are manufacture to provide long lasting services for so many years, all the aircraft must be in an airworthy state and have to be safe to fly. Thus maintenance programmes must be carried out to maintain the aircraft and also aircraft must be operated according to the manufacturers’ recommendation.
Florio F. (2006) stated that, older aircraft require additional care and the maintenance programmes must be carried out in a more specific way than the recently manufactured aircraft. And also he stated that due to the fatigue, accidental damage and also due to the environmental deterioration more inspection in the components of the structure must require in maintenance programmes. So to maintain airworthiness in older aircrafts manufacturers of the flight has to provide operators with the specific programs. In older aircrafts normally each of the aeroplane components have to undergo some of the repairs, overhauls, inspection maintenance, preventive maintenance and some replacements of components of the aircraft.
Maintenance records have to be update regularly by the operator. Florio F. (2006) states that between operator of the aircraft, manufacturer and also the authority there should be an open communication system. Furthermore he states that once a problem occur the operator or the owner of the aircraft must inform it to the manufacturer and then manufacturer has to prepare the recommendations and has to update the appropriate programmes of continued air worthiness. After examination of those maintenance programmes the authorities will approve those.
Role of the Regulator
Airworthiness programmes consist of three main roles.
Civil Aviation Authority (CAA), European Aviation Safety Agency (EASA) and Federal Aviation Regulations (FAR) are examples for the regulation authorities. These authorities generate and distribute the regulations for aircraft operations for aviation industry.
Civil Aviation Authority is the UKs independent specialist regulator. Their main responsibility is to provide world leading air safety environment in the aviation industry. Aircraft licensing, maintenance of specific airworthiness management systems and economic regulations, consumer protection, policies for airspace and setting up national safety standards can be taken as key role of CAA.
Regulators involved in few or many roles as follows:
Setting up the civil aviation standards and ensure they are achieved.
Regulates and encourages airlines, airports and national air traffic services economic activities etc…
Manages the principal travel protection scheme.
Ensure the airspace is a common place for all users by bringing civil and military interests together.
Advise the government on aviation issues.
Represents consumer interests
Conduct scientific and economic research.
Provide specialist services by producing statistical data.
Conclusion & Recommendation
Aircraft airworthiness means compliance with applicable aviation authorities regulations that defines the minimum safety level of the aircraft, of the passengers transported and the over flown territories and when designed and built according to applicable requirements, when operated within its’ intended environment and within its’ quantified and declared limitations and maintained in accordance with procedures acceptable to the responsible Authority. Therefore, The Airworthiness is a collective responsibility of operators, authorities, manufactures and maintenance organisations.
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