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Airworthiness
An Introduction to Aircraft Certification
By Filippo De Florio
Butterworth-Heinemann
Copyright © 2006 Filippo De Florio
All right reserved.
ISBN: 978-0-08-046201-1
Chapter One
Flight Safety
Safety is a concept generally ingrained in the human mind; we will consider 'absence of danger' as its principal definition. Safety is something related to all human activities and therefore every civil society is organized (or should be organized) to guarantee public safety in relation to one's own or others' activities. This is certainly a moral obligation, but it is also a practical demand because accidents, causing damage to persons and properties, have a social cost. This is also the reason why human activities that could cause damage to persons and properties are controlled by national states through regulations.
We will deal specifically with safety related to aeronautical activities, starting by considering what we have defined as the main conventional flight safety factors: man, the environment, and the machine.
1 Man is intended here as an active part of the flight operations; we then consider pilots, maintenance manpower, air traffic controllers, and others. Clearly, it is important to be able to rely on very skilled people in order to avoid errors that cause accidents or catastrophes in flight operations. It is then of paramount importance to place these people in a legislative and organized context to guarantee a suitable level of professional training, updating of techniques and procedures, and psychological and physical fitness. National states entrust special public institutions with the responsibility for such obligations.
2 The environment covers all the external factors that can have an influence on the flying of an aircraft. This includes meteorological conditions, traffic situations, communications, aerodromes, etc. It is equally important to avoid situations that could jeopardize the aircraft itself. Then we should consider correct meteorological information, rules for the vertical and horizontal separation of the aircraft, suitable aerodromes, etc.
3 The machine does not need a definition, but it is easy to understand the importance of a good project, sound construction, and efficiency in relation to the operations to be carried out. Also, in this case, national states entrust special public bodies with the responsibility of assuring that the project, the construction, and the operating instructions comply with flight safety.
An important point regarding these safety factors is that they act in series and not in parallel. They can be seen as three links of a chain representing flight safety.
The failure of a single link is sufficient for an accident to happen. A pilot's error can put the best aircraft in jeopardy, and the best pilot cannot compensate for a serious failure in an aircraft. Accident reports offer countless examples of this; however, accidents are often caused by a combination of factors that could involve all these safety factors. Nevertheless, the accident always begins with the failure of one of the above-mentioned links.
In this book we will deal particularly with one of these safety factors: the machine.
We will discuss design rules, the people who make them, who formulates the verifications from design to construction, and who is responsible for the organization of manufacturers and operators.
We are going to deal with airworthiness.
Chapter Two
Airworthiness
A definition of 'airworthiness' can be found in the Italian RAI-ENAC Technical Regulations: 'For an aircraft, or aircraft part, [airworthiness] is the possession of the necessary requirements for flying in safe conditions, within allowable limits.'
In this definition, three key elements deserve special consideration: safe conditions, possession of the necessary requirements, and allowable limits.
1 We can take for granted the meaning of safe conditions relating to the normal course and satisfactory conclusion of the flight.
According to one definition, safety is the freedom from those conditions that can cause death, injury or illness, damage to/loss of equipment or property, or damage to the environment.
2 Possession of the necessary requirements means that the aircraft, or any of its parts, is designed and built according to studied and tested criteria to fly in safe conditions, as mentioned above.
Regulations are intended to promote safety by eliminating or mitigating conditions that can cause death, injury, or damage.
Who establishes these regulations? The airworthiness authorities appointed by the national states. These are obtained through the publication of airworthiness standards (see details in the following chapters) containing a series of design requirements: from the strength of the structures to the flight requirements (flight qualities and performance), criteria for good design practice, systems, fatigue and flutter, necessary tests, flight and maintenance manual content, and so on. These standards are different for different types of aircraft. Obviously, it is not possible to design a sailplane, a 'Jumbo', or a helicopter using the same rules. An important peculiarity of these standards is their evolution as time passes. Generally, a standard does not precede aeronautical progress, it follows it and sometimes accompanies it. A 'blocked' standard would prevent aeronautical progress. It follows that the rules have to continuously fit with technical aeronautical evolution. Moreover, very often accident analysis leads to additional rules which, had they been applied to the design, might have prevented the accident or at least limited its effects; this process could be regarded as 'afterthoughts', but it is better to consider it as 'experience'. The changing of the standards (normally with the purpose of adding something new or different) makes the design compliance to the rules more and more expensive, but this is the price to pay to improve flight safety.
3 Allowable limits. Aircraft are designed for operation within a certain 'flight envelope', which depends mainly on speed and structural load factors. In addition, the maximum weight of the aircraft can be established differently for different types of operations. Operational conditions of the aircraft, such as day-VFR, night flight, instrumental flight, in or out of icing conditions, etc., are also established. Exceeding these conditions and limits can cause accidents. Overweight take-off, aerobatic maneuvers performed with aircraft designed with load factors for non-aerobatic operations, flights in icing conditions without suitable protection, and exceeding the speed limits are just a few examples of the importance of flying within the allowable limits. Pilots are made aware of these limits through the flight manual, through the markings and placards displayed in the cockpit, and of course through training.
Chapter Three
The ICAO and the Civil Aviation Authorities
3.1 The ICAO (International Civil Aviation Organization)
The first recorded flight by a heavier-than-air machine was by the Wright brothers on 17 December 1903 in North Carolina.
Since the earliest years of aviation, far-seeing people envisaged a new dimension of transport that would go beyond national boundaries. In 1910, the first conference on air navigation international law was hosted by France in Paris, with the attendance of 18 European states.
The First World War fostered considerable development of aeronautical techniques, also demonstrating the potential for transport of goods and people. After the war, it became increasingly evident that this advanced means of transport would require international attention.
These problems were debated at the Paris Conference of Peace in 1919, and the discussions led to the establishment of an Aeronautical Commission. To succeed in the purpose of making aviation an instrument of peace, an International Air Convention was written and ratified by 38 states. The Convention contemplated all aspects of civil aviation and also the establishment of an International Commission for Air Navigation (ICAN) in order to monitor the development of civil aviation and to propose measures for this development.
The years between the two world wars marked a continuous development of civil aviation both in the technical and the commercial fields.
The Second World War, apart from the horrors also caused by the operations of progressively more sophisticated military aeroplanes, had a major effect upon the technical development of the aeroplane, compressing a quarter of a century of normal peacetime development into six years.
The possibility of carrying a great number of people and a large quantity of goods over long distances became a reality. For these reasons, the Government of the United States conducted exploratory discussions with other allied nations from the early months of 1944. On the basis of these talks, invitations were sent to 55 allied and neutral states to meet in Chicago in November 1944. Of these 55 states, 52 attended. The outcome of five weeks of meetings was the Convention on International Civil Aviation, consisting of a preamble and 96 articles.
The ICAO officially came into existence on 4 April 1947. At the invitation of the Government of Canada, Montreal was chosen as the site for its headquarters. Presently, the Contracting States number more than 180.
The aims and objectives of the ICAO are to develop the principles and techniques of international air navigation and to foster the planning and development of international air transport so as to:
1 Ensure the safe and orderly growth of international civil aviation throughout the world.
2 Encourage the arts of aircraft design and operation for peaceful purposes.
3 Encourage the development of airways, airports and air navigation facilities for international civil aviation.
4 Meet the needs of the peoples of the world for safe, regular, efficient and economical air transport.
5 Prevent economic waste caused by unreasonable competition.
6 Ensure that the rights of the Contracting States are fully respected and that every Contracting State has a fair opportunity to operate international airlines.
7 Avoid discrimination between Contracting States.
8 Promote safety of flight in international air navigation.
9 Promote generally the development of all aspects of international civil aeronautics.
3.1.1 The International Standards
Since the ICAO was created, a main technical task of the organization has been the achievement of standardization in the operation of a safe, regular and efficient air service. This has resulted in high levels of reliability in the many areas that collectively shape international civil aviation, particularly in relation to the aircraft, their crews, and the ground-based facilities and services.
Standardization has been achieved through the creation, adoption, and amendments of 18 Annexes to the Convention, identified as International Standards and Recommended Practices.
Standards are directives which ICAO members agree to follow. If a member has a standard different from an ICAO Standard, that member must notify the ICAO of the difference.
Recommended practices are desirable but not essential practices. The basic principle for deciding whether a particular issue should be a Standard is an affirmative answer to the question: 'Is uniform application by all Contracting States essential?'
On the basis of the Convention, the Contracting States are engaged to achieve the highest practical degree of worldwide uniformity in regulations, organizing procedures in relation to aircraft, personnel, airways, and auxiliary services, whenever this will facilitate and improve air safety, effectiveness, and regularity.
The 18 Annexes are described as follows:
• Annex 1. Personnel Licensing – provides information on licensing of flight crews, air traffic controllers, and aircraft maintenance personnel, including medical standards for flight crews and air traffic controllers.
• Annex 2. Rules of the Air – contains rules relating to visual and instrument-aided flight.
• Annex 3. Meteorological Service for International Air Navigation – provides meteorological services for international air navigation and reporting of meteorological observations from aircraft.
• Annex 4. Aeronautical Charts – contains specifications for the aeronautical charts used in international aviation.
• Annex 5. Units of Measurement to be used in Air and Ground Operations – lists dimensional systems to be used in air and ground operations.
• Annex 6. Operation of Aircraft – enumerates specifications to ensure a level of safety above a prescribed minimum in similar operations throughout the world. The three parts of this Annex are as follows:
– Part I. International Commercial Air Transport – Airplanes
– Part II. International General Aviation – Airplanes
– Part III. International Operations – Helicopters.
(Continues...)
Excerpted from Airworthiness by Filippo De Florio Copyright © 2006 by Filippo De Florio. Excerpted by permission of Butterworth-Heinemann. All rights reserved. No part of this excerpt may be reproduced or reprinted without permission in writing from the publisher.
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