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FLIGHT SAFETY, AIRWORTHINESS,

TYPE CERTIFICATES, DESIGN REQUIREMENTS

AND SPECIFICATIONS

Serkan Özgen, Prof. Dr.

Middle East Technical University, Dept. Aerospace Eng., Turkey

1. Introduction

This manuscript aims at outlining the basic concepts of flight safety, airworthiness, type

certificates, design requirements and specifications that are of paramount importance for

aircraft design. It is a well-known fact that safety and airworthiness requirements are

becoming more and more stringent and complex parallel to the quest for a safer, greener,

cheaper, faster and more efficient air transportation. The designer therefore, shall keep safety

and airworthiness considerations in mind starting from the earliest stages of the design since

these are prerequisites for a technically sound, feasible, safe and a reliable airplane.

In the following, first the basic concepts of flight safety and airworthiness are defined. Then,

information on civil aviation authorities that are responsible for maintaining safe, regular and

efficient air services around the globe are given. Airworthiness Requirements and Type

Certification discussions constitute the following two sections of the manuscript. Finally,

some important design requirements and specifications mentioned in relevant airworthiness

codes are summarized. The information given in the manuscript is largely compiled from

open references including JAA (Joint Aviation Authorities), EASA (European Aviation

Safety Agency) and FAA (Federal Aviation Administration) documents, and as such can be

regarded as a concise review of the current state of the topic.

2. Flight Safety

Safety can be defined to be the control of recognized hazards to achieve an acceptable level of

risk. Safety is related to all human activities, and all human activities that could cause damage

to persons and properties are controlled by national states through regulations.

Since we are specifically dealing with safety related to aeronautical activities, the main

conventional flight safety factors need to be defined: man, environment, and machine [1].

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i. Man is an active part of the flight operations considering pilots, maintenance crew,

traffic controllers and others. In order to avoid errors that cause accidents in flight

operations, very skilled and trained people must be relied upon. It is of paramount

importance to place these people in a legislative and organized context to guarantee an

adequate level of professional training, psychological and physical fitness.

ii. The environment covers all the external factors that can have an influence on the

flying of an aircraft including meteorological conditions, traffic, communications, etc.

iii. For the machine, it is easy to understand the importance of a good design, sound

construction, and efficiency in relation to the operations to be carried out.

These safety factors act in series and not in parallel. A failure of a link is sufficient for an

accident to happen. Nevertheless, accident reports suggest that accidents are usually caused

by a combination of factors that involves more than one or all of the safety factors.

Airworthiness deals particularly with the machine aspect of the flight safety.

3. Airworthiness

Airworthiness can be defined as the ability of an aircraft or any other airborne equipment or

system to operate without significant hazard to aircrew, ground crew, passengers or to the

general public over which such airborne systems are flown [2]. In order to accomplish this,

the aircraft must comply with necessary requirements for flying in safe conditions, within

allowable limits [1].

i. Safe conditions apply to normal beginning, continuation in normal course and

satisfactory termination of flight.

ii. Compliance with necessary requirements means that the aircraft, or any of its parts,

is designed and built according to studies and tested criteria to fly in safe conditions.

iii. Aircraft are designed for operation within an operating envelope, which mainly

depends on speed and structural load factors. For example, overweight take-off, flights

in icing conditions without adequate protection and exceeding the speed limits may

impose a risk on flight safety.

4. ICAO and Civil Aviation Authorities

4.1. ICAO – International Civil Aviation Organization

Since the foundation of ICAO in 1947, the main technical task of the organization has been

the achievement of standardization in the operation of a safe, regular, and efficient air

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service worldwide. This has resulted in high levels of reliability in many areas that

collectively shape international civil aviation, particularly in relation to the aircraft, their

crews, and the ground-based facilities and services [1].

Standardization has been achieved through the creation, adoption, and amendments of 18

annexes identified as International Standards and Recommended Practices [1].

i. International Standards are directives that ICAO members agree to follow. They are

considered as necessary for the safety and regularity of international air navigation.

ii. Recommended practices are desirable but not essential. Their application is

considered as a recommendation in the interest of safety, regularity, and efficiency of

international air navigation.

Airworthiness standards for the certification of aircraft to be internationally recognized are

issued in accordance with the ICAO annexes. The certification process is based on these

airworthiness standards rather than directly on the ICAO International Standards [1].

The annex that is most relevant to the scope of the VKI Short Course: UAVs & Small Aircraft

Design is Annex 8-Airworthiness of Aircraft. The technical standards dealing with the

certification of airplanes include requirements related to performance, flying qualities,

structural design and construction, engine and propeller design and installation, systems and

equipment design and installation, and operating limitations including procedures and general

information to be provided in the airplane flight manual, crashworthiness of aircraft and cabin

safety, operating environment, and human factors and security in aircraft design [1].

Special consideration is given to requirements design features affecting the ability of the flight

crew to maintain controlled flights. The layout of the flight crew compartment must be such

as to minimise the possibility of the incorrect operation of controls due to confusion, fatigue

or interference. It should allow for a sufficiently clear, extensive, and undistorted field of

vision for the safe operation of the airplane [1].

Airplane design features also provide for the safety, health and well-being of occupants by

granting an adequate cabin environment during the foreseen flight and ground and water

operating conditions, the means for rapid and safe evacuation in emergency landings and the

equipment necessary for the survival of the occupants in the foreseen external environment

within a reasonable time span [1].

Requirements for the certification of engines and accessories are designed to ensure that they

function reliably under the foreseen operating conditions [1].

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4.2. Civil Aviation Authorities

A civil aviation authority or a regulatory authority is a government statutory authority in

each country that oversees the approval and regulation of civil aviation. A regulatory

authority in the sense used here is usually a national aviation authority (NAA) [3].

A regulatory authority typically regulates the following critical aspects of aircraft

airworthiness and their operation [3]:

Design of aircraft and related products, parts and appliances.

Maintenance of aircraft and equipment.

Operation of aircraft and equipment.

Licensing of pilots and maintenance engineers.

Licensing of airports and navigational aids.

Standards for air traffic control.

Depending on the legal system of the parent country, the regulatory authority will derive its

power from an act of the Parliament such as the European Parliament for the EASA. The

regulatory authority is then empowered to make regulations within the bounds of the act.

Table 1 summarizes the authorizations of regulatory organizations for the issuance of

certificates and approvals in the EU [4].

Table 1. Authorizations of regulatory organizations

for the issuance of certificates and approvals in the EU [4].

Certificate of Approval,

Permit to Fly

Issued by

EASA Competent

authority

Design

organisation

Production

organisation

Type Certificate (TC),

Restricted Type

Certificate (RTC),

Supplementary Type

Certificate (STC)

X

Changes X X

Repairs X X

Certificate of

airworthiness X

Noise certification X

Permit to fly X X X

Design organisation

approval X

Production organisation

approval X1

1 By EASA when the applicant is a legal entity in a country, which is not a member of EASA.

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Some of the major aviation regulatory authorities are:

Federal Aviation Administration (FAA, USA);

European Aviation Safety Agency (EASA, EU). EASA is not actually a NAA but

plays part of the role within its member states of the EU;

Civil Aviation Authority (CAA, UK);

Direction Générale de l’Aviation Civile (DGAC, France);

Luftfahrt-Bundesamt (LBA, Germany);

Transport Canada (TC, Canada);

Directorate General of Civil Aviation (SHGM, Turkey).

5. Airworthiness Requirements

5.1. Airworthiness Codes

Airworthiness codes are established by regulatory authorities and contain a series of design

requirements including strength of structures, flight qualities, performance, criteria for good

design practice, systems, necessary tests, flight and maintenance manual content, etc. Some of

the most prominent airworthiness codes are given in Table 2 [4], while the regulation

structure in EASA is shown in Figure 1 [1].

Table 2. Airworthiness codes (certification specifications or federal regulations) [4].

Code Organization Definition

CS-Definitions/FAR-1 EASA/FAR Definitions used in other CS/FAR documents

Part-21/FAR-21 EASA/FAR Certification procedures for aircraft and related

products and parts

CS-VLA EASA CS for very light airplanes

CS-VLR EASA CS for very light rotorcraft

CS-22 EASA CS for sailplanes and powered sailplanes

CS/FAR-23 EASA/FAA CS/FR for normal, utility, acrobatic, commuter

category airplanes

CS/FAR-25 EASA/FAA CS/FR for large airplanes

CS/FAR-27 EASA/FAA CS/FR for small rotorcraft

CS/FAR-29 EASA/FAA CS/FR for large rotorcraft

FAR-31 FAA FR for manned free balloons

CS/FAR-34 EASA/FAA CS/FR for aircraft engine emissions and fuel venting

CS/FAR-36 EASA/FAA CS/FR for aircraft noise

CS-AWO EASA CS for all weather operations

CS-E/FAR-33 EASA/FAA CS/FR for engines

CS-ETSO EASA CS for European Technical Standard Orders

CS-P/FAR-35 EASA/FAA CS/FR for propellers

CS-LSA EASA CS for light sport airplanes

CS-APU EASA CS for auxiliary power units

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Figure 1. EASA regulation structure [1].

Types and categories of specific aircraft relevant to the present context are given below.

5.1.1. CS-VLA. Very Light Aeroplanes [5]

This includes airplanes with:

Single engine with spark or compression ignition;

Maximum two seats;

Maximum certified take-off gross weight ≤ 750 kg;

Stalling speed in landing configuration ≤ 45 knots (83 km/h).

CS-VLA applies to airplanes intended for non-aerobatic use only. These are:

Any manoeuvre incident to normal flying;

Stalls (except whip stalls);

Lazy eights, chandelles, and steep turns in which the bank angle is 60° or less.

Approval is to be given only for day-VFR.

5.1.2. CS-LSA Light Sport Aeroplanes [6]

This certification specification is applicable to airplanes to be approved for day-VFR only that

meet all of the following criteria:

Maximum take-off mass ≤ 600 kg;

Stalling speed in landing configuration ≤ 45 knots (83 km/h);

Maximum two seats;

A single, non-turbine engine or electric propulsion unit fitted with a propeller;

Non-pressurized cabin.

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5.1.3. FAR/CS-23. Normal, Utility, Aerobatic and Commuter Category Aeroplanes [7]

i. Aeroplanes in the normal, utility, and aerobatic categories that have a seating

configuration, excluding the pilot seat(s), of nine or fewer and a maximum certified

take-off weight of 5670 kg (12 500 lb) or less;

ii. Propeller-driven, twin engine aeroplanes in the commuter category that have a seating

configuration, excluding the pilots seat(s), of 19 or fewer and a maximum certified

take-off weight of 8618 kg (19 000 lb) or less.

Airplane categories are as follows:

i. Normal. The Normal Category is limited to non-aerobatic operations. Non-aerobatic

operations include stalls (except whip stalls) and some simple manoeuvres in which

the bank angle is not more than 60°.

ii. Utility. The Utility Category is limited to the operations in the Normal Category,

spins, and some aerobatic manoeuvres, where the bank angle is between 60° and 90°.

iii. Aerobatic. The Aerobatic Category has no restrictions other than those shown to be

necessary as a result of required flight tests.

iv. Commuter. The Commuter Category is limited to any manoeuvre incident to normal

flying, stalls (except whip stalls) and steep turns in which the bank angle is 60° or less.

For single-engined Normal, Utility and Aerobatic Category Airplanes, and twin-engined

airplanes in the same Category that cannot satisfy a specified climb rate requirement with one

engine inoperative, stalling speed in landing configuration must be less than or equal to 61

knots (113 km/h).

5.1.4. FAR/CS-25. Large Aeroplanes [8]

These are turbine powered large airplanes. There are no limitations related to weight or

number of occupants for airplanes in this Class.

5.2. Structure of Aircraft Airworthiness Standards [1]

If the airworthiness codes for certification like CS-22, CS-VLA, CS-VLR, CS/FAR-23, 25,

27, and 29 are examined, it will be noticed that all have a common structure. These

documents are composed of subparts and appendices, and same topics are dealt with

paragraphs having the same number. For example, XX.25 is for “Weight Limits”, while

XX.125 is for longitudinal control.

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A brief description of the subparts are as follows:

Subpart A: General. This subpart provides information about the types and categories of

aircraft to which the standard is applicable.

Subpart B: Flight. This subpart deals with the flight tests to be carried out to show

compliance with performance, controllability, manoeuvrability and stability requirements.

Subpart C: Structure. This subpart contains the requirements for flight (manoeuvre and gust

loads) and ground load assessment, and for structural design of airframes, control systems,

landing gears, and others. Crashworthiness and fatigue requirements are also provided.

Subpart D: Design and Construction. This subpart deals with the design technique,

materials, safety factors, control system and landing gear design, structural tests to be carried

out, cockpit and passenger cabin design, fire protection and flutter requirements.

Subpart E: Powerplant. This subpart contains the requirements for power plant installations

and related systems. Powerplant controls, accessories, and fire protection are also considered.

Subpart G: Operating Limitations and Information. This subpart provides requirements

for all the information that must be available to the pilot and other personnel for correct

aircraft operations like markings, placards, and the content of the flight manual.

Appendices. These may provide design load criteria, test procedures for material

flammability, and instructions for continued airworthiness.

5.3. Severity of the airworthiness standards [1]

The application of an airworthiness rule involves expense. Increase of safety is not always

proportional to the severity of the rule. At and beyond a certain level of safety, negligible

safety increases incur great cost. At this point, the rule is not practicable, Figure 2.

A rule of thumb in airworthiness rulemaking is that, a proposal should be:

i. Economically reasonable;

ii. Technologically practicable;

iii. Appropriate to the particular type of aircraft.

Various airworthiness standards have been produced for different types of aircraft (airplanes,

rotorcraft, etc.) and also for different categories of the same type of aircraft (according to

weight, number of passengers, etc.). The aircraft are arranged in groups that are as

homogeneous as possible. For example, a distinction is made in CS/FAR-23 between Normal,

Utility, Aerobatic, and Commuter airplanes. This does not imply that airworthiness standards

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are higher for transport airplanes than others because they must be safer. Safety must be

maximized for all aircraft within the practicability concept mentioned above, i.e. simple

aircraft should have simple airworthiness standards to comply with. As an indication of this,

CS-25 is 919 pages, CS-23 is 405, and CS-VLA is only 121! The designer should be capable

of choosing the right airworthiness standard with respect to the design project.

Figure 2. Severity of airworthiness rules [1].

5.4. Stalling Speed for Single-Engine Airplanes [1]

Single-engine airplanes are regulated according the stalling speed. It is obvious that, when the

engine of a single engine airplane fails, it can only glide. Therefore, it is necessary that

gliding and the power-off landing of a single-engine airplane does not require outstanding

pilot skill or effort. For this reason, a limitation on the stall speed is required because a power-

off landing is a function of the approach speed, which is itself dependent on the stall speed in

the landing configuration. Therefore, the stalling speed of single-engine airplanes in landing

configuration is limited to 61 knots (113 km/h). The same limitation holds for twin-engine

airplanes that cannot maintain a minimum steady rate of climb with one engine inoperative.

For other twin-engine airplanes or large airplanes, no stalling speed requirement exists.

For CS-VLA and CS-LSA Class airplanes, the stalling speed limitation is 45 knots (85 km/h)

on the basis of above-mentioned reasons, because in principle, engines that are fitted to such

airplanes are less reliable than those installed on CS/FAR-23 airplanes.

5.5. Crashworthiness [1]

Obviously, the stalling speed limitation considered above cannot guarantee a safe power-off

landing since it cannot take all the conditions during landing into consideration, like rough

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ground for example. Then, the possibility of a crash must be considered, which brings us to

the discussion on crashworthiness. Crashworthiness concerns all types of airplanes.

CS/FAR-23 contains appropriate safety standards for emergency landing conditions. It deals

with structural rules for the protection of the occupants, requiring extensive static and

dynamic tests for the seat/restraint system, the seats, and the fuselage structure supporting

these. CS-VLA contains a section dealing with emergency landing conditions, providing

requirements for rapid escape in normal and crash attitude. Dynamic crash tests are not

required for these airplanes.

5.6. Fire Protection [1]

An aircraft has engines, fuel, electrical installations making fire hazard a real threat. For fire

protection, fire zones, locations where fire may develop first need to be identified. These are

the engine compartment, fuel tanks, etc. There are three methods for protecting the occupants

of an airplane from fire:

i. Abandoning the aircraft.

ii. Passive protection to contain the fire for a time necessary for landing.

iii. Active protection by means of extinguishers.

In civil aircraft, passive protection is prescribed to allow a safe emergency landing, whenever

possible. This is achieved by suitable isolation of the fire zones so that essential structures and

systems can be protected until landing. Fire extinguishers are not considered as primary

protection, but their use is not excluded.

Active protection, by means of fixed or portable extinguishers is prescribed in transport and

commuter category airplanes in order to put out accidental fires in the cockpit, the cabin, the

engines, and the baggage and cargo compartments.

The airworthiness standards provide rules for materials used for the cabin interiors, from

flammability and noxious smoke emissions points of view.

Since the requirements must be substantiated by tests, the certification standards provide

procedures for such tests as means of compliance.

5.7. Safety Assessment [1]

Ideally, the reliability of a vital aircraft system should have a 100% reliability. However,

achieving such a reliability level is practically impossible. Reliability of a system can be

improved with redundancy. However, a system with a high degree of redundancy would be

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heavy, expensive, and complex. It is more convenient to design systems with a minimum

degree of redundancy through increasing the reliability of single components. This ensures an

acceptable safety level.

Failure conditions are defined as effects on the aircraft and its occupants, both direct and

consequential, caused or contributed by one or more failures, considering relevant adverse

operational or environmental conditions. Failure conditions are classified according to their

severity as follows:

i. Minor. Failure conditions that do not reduce airplane safety significantly. These

involve crew actions well within their capability.

ii. Major. Failure conditions that would reduce the capability of the airplane or the ability

of the crew to cope with adverse operating conditions. Significant reductions in safety

margins or functional capabilities or a significant increase in crew workload may

result. Discomfort to occupants, possibly injuries may occur.

iii. Hazardous. Failure conditions that would reduce the capability of the airplane or the

ability of the crew to cope with adverse operating conditions such that large reductions

in safety margins or functional capabilities occur. Physical distress or workload of the

flight crew is so high that the flight crew cannot perform their tasks accurately or

completely. Serious or fatal injury to a small number of occupants may result.

iv. Catastrophic. Failure conditions that would prevent continued safe flight and landing.

An inverse relationship exists between the severity of failure conditions and probability of

occurrence, which is also illustrated in Figures 3 and 4:

i. Minor failures are probable and could arise several times in the aircraft’s life.

ii. Major failures are remote (~10-5), might arise once in an aircraft’s life and would arise

several times in the whole fleet’s life.

iii. Hazardous conditions are extremely remote (~10-7), might arise once in the whole

fleet’s life.

iv. Catastrophic conditions are extremely improbable (~10-9), are unlikely to arise in the

whole fleet’s life.

The safety assessment of equipment, systems, and installation is a very important part of

aircraft design. The techniques of safety assessment are a specialist matter and it is very

important to start the assessment from the very early phases of design. Late assessments will

obviously result in expensive design changes and delays (which are also expensive).

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Figure 3. Classification of failure conditions [1].

Figure 4. Relationships between probability and severity of failure conditions [1].

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5.8. Fatigue Strength [1]

The airworthiness standards consider two kinds of aircraft structure:

i. Single load path structures. Applied loads are distributed through a single member,

the failure of which would result in the loss of the structural capability to support the

applied loads. A wing-fuselage attachment made by a single structural element like in

most light aircraft is an example to such a design.

In this case, the structure must result in safe-life and must be able to sustain a number

of cycles during which there is a low probability of the structure to degrade below its

ultimate design load value due to fatigue.

ii. Multiple load path structures. These are redundant structures in which the applied

loads would be safely distributed to other load-carrying members in case of the failure

of an individual element.

In this case, the structure is damage-tolerant, it is able to retain its residual strength

for a period without being repaired after a failure or partial failure occurs due to

fatigue, corrosion, etc. This kind of structure is called fail-safe.

For large airplanes, the airworthiness standards (CS/FAR-25), require fail-safe structures,

except when it is not possible to implement such a design due to geometrical restrictions. An

example to such a case is the landing gear and its attachments.

For CS/FAR-23 airplanes, it is possible to choose among safe-life and fail-safe approaches.

An exception to this is composite airframes, where the design must be accomplished

according to fail-safe criteria.

In the case of loads and loading spectra, the assumptions made for fatigue assessment are:

i. For CS/FAR-25 and CS/FAR-23 airplanes, the principal loads that should be

considered in establishing a loading spectrum are flight loads (gust and manoeuvre),

ground and pressurization loads. In assessing the possibility of serious fatigue failures,

the design is examined to determine possible points of failure in service. In this

examination, results for stress analysis, static and fatigue tests, strain gauge surveys,

tests of similar configurations and service experience are considered.

ii. For CS-VLA airplanes, it is recommended that stress concentration areas are avoided

as much as possible and fatigue tests are performed only when they are necessary.

Instead, reference is made to data resulting from fatigue tests on similar structures and

service experience. A way to avoid fatigue tests is to design critical structures with

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stress levels below the fatigue limit of the material used. This must be demonstrated

by static tests and strain gauge surveys.

6. Type Certification

6.1. Type Certificate

A type certificate is an approval made by a regulatory authority that an aircraft is

manufactured according to an approved design, and that the design ensures compliance with

airworthiness requirements [9].

The type certificate (TC) implies that the aircraft manufactured according to the approved

design can be issued an Airworthiness Certificate. To meet airworthiness requirements, the

aircraft, related products (engine and propeller), parts and appliances must be approved [9].

Within the European Union (EU), implementation rules for type certification are laid down by

the Commission Regulation (EU) No 748/2012 of 3 August 2012 titled:

Laying down implementing rules for the airworthiness and environmental

certification of aircraft and related products, parts and appliances, as well as

for the certification of design and production organisations.

Annex I (Part 21) of this regulation specifically addresses “Certification of aircraft and related

products, parts and appliances, and of design and production organisations”. Subpart B of

Section A of this regulation establishes the procedures for issuing type certificates for

products and restricted type certificates for aircraft, and establishes the rights and obligations

of the applicants for, and holders of, those certificates. The following text is from EASA Part

21 [10]. FAR-21 has slightly different wording, but with the same meaning.

6.2. Eligibility and Demonstration of Capability (EASA Part 21, 21.A.13 and 21.A.14)

a) An organization applying for a type certificate or a restricted type certificate shall

demonstrate its capability by holding a Design Organisation Approval.

b) As an alternative procedure to demonstrate capability, the applicant may seek the

agreement of EASA when the product is one of the following:

i. an ELA2 aircraft;

ii. an engine or propeller installed on a ELA2 aircraft;

iii. a piston engine;

iv. a fixed or adjustable pitch propeller.

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c) An applicant may choose to demonstrate its capability by providing EASA with the

certification program if the product is one of the following:

i. an ELA1 aircraft;

ii. an engine or propeller installed on an ELA1 aircraft;

European Light Aircraft 1 (ELA 1) means the following in the present context:

i. An airplane with a maximum take-off mass (MOTM) ≤ 1200 kg w/o a complex motor;

ii. A sailplane or powered sailplane with MOTM ≤ 1200 kg.

European Light Aircraft 2 (ELA 2) means the following in the current context:

i. An airplane with a maximum take-off mass (MOTM) ≤ 2000 kg w/o a complex motor;

ii. A sailplane or powered sailplane with MOTM ≤ 2000 kg.

Balloons, hot air airships, very light rotorcraft may also be considered as ELA1 or ELA2

aircraft, but this is outside the present context.

6.3. Main Characteristics of a Design Organization

The main duties of a design organization are as follows [1]:

i. To design.

ii. To demonstrate compliance with the applicable requirements.

iii. To check the statements of compliance independently.

iv. To provide items for continued airworthiness.

v. To check the work performed by partners/subcontractors.

vi. To monitor the above functions independently.

vii. To provide the authority with the compliance documentation.

viii. To allow the authority to make any inspection and any flight and ground tests

necessary to check the validity of compliance.

A design organization should also have an established design assurance system for control

and supervision of the design and design changes of the product covered by the application.

This includes all the activities for the achievement of the type certificate, the approval of

changes, and the maintenance of continued airworthiness [1].

6.4. Application (EASA Part 21, 21.A.15)

a) An application for a type certificate shall be made in a form and manner established by

EASA.

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b) An application for an aircraft type certificate shall include a three-view drawing of the

aircraft and preliminary basic data, including the proposed operating characteristics and

limitations.

c) An application for an engine or propeller type-certificate shall include a general

arrangement drawing, a description of the design features, the operating characteristics,

and the proposed operating limitations.

6.5. Airworthiness Codes (EASA Part 21, 21.A.16A)

The Agency shall issue airworthiness codes as standard means to show compliance of

products, parts and appliances with the essential requirements of Annex I (Part 21). Such

codes shall be sufficiently detailed and specific to indicate to applicants the conditions under

which certificates will be issued.

6.6. Special Conditions (EASA Part 21, 21.A.16B)

a) EASA shall prescribe special technical specifications for a product if the related

airworthiness code does not contain adequate or appropriate safety standards for the

product because:

i. The product has novel or unusual design features;

ii. The intended use of the product is unconventional;

iii. Experience with other similar products in service or products having similar features,

has shown that unsafe conditions can develop.

b) Special conditions contain safety standards to establish a level of safety equivalent to that

established by the applicable airworthiness codes.

6.7. Acceptable Means of Compliance

The term Acceptable Means of Compliance (AMC) is used to qualify technical interpretative

material to be used in the certification process. In this respect, the AMC serve as means by

which the certification requirements can be met by those subject to the Regulation [11].

AMC material is not binding on those applying for regulatory approval, who may decide to

show compliance with the applicable certification requirements using other means. Competent

NAAs may also produce their own acceptable means of compliance, based or not on those

issued by EASA or FAA. Such national means of compliance cannot bind the applicants

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either; the applicant can choose to comply by other means; however, such alternative means

of compliance must be approved by the competent authority [11].

Some examples to means of compliance are as follows [1]:

Calculation/analysis. Reports for the evaluation of loads, strength, performance, flying

qualities, or other characteristics.

Safety assessment. Documents describing safety analysis philosophy and methods,

safety evaluation plans, system safety assessment, zonal safety assessment and others.

Flight tests. Reports of flight tests written in the Flight Test Program and performed by

a flight test crew.

Inspections. Conformity inspections to verify that materials, parts, processes, and

fabrication procedures conform to the type design. Aircraft inspection to verify the

compliance with the requirement, which cannot be determined adequately from the

evaluation of technical data only.

6.8. Certification Basis (EASA Part 21, 21.A.17)

a) The type certification basis for the issuance of a type certificate consists of:

i. The applicable airworthiness code established by the agency, effective on the date of

application.

ii. Any special condition prescribed in accordance with subsection 21.A.16B.

b) An application for type certification of large airplanes and rotorcraft will remain effective

for five years, and an application for any other type certification shall be effective for three

years. The Agency may approve a longer period if the applicant shows that the product

requires a longer time for design, development and testing.

c) In the case where a type certificate has not been issued or it is clear that it will not be

issued within the time limit established under paragraph b) above, the applicant may either

file a new application or file for an extension of the original application.

d) If an applicant chooses to comply with a certification specification of an amendment to the

airworthiness codes that is effective after the filing of the application for a type certificate,

the applicant shall also comply with any other certification specification that the agency

finds is directly related.

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6.9. Designation of Applicable Environmental Protection Requirements and

Certification Specifications (EASA Part 21, 21.A.18)

a) The applicable noise requirements for subsonic jet airplanes, propeller-driven airplanes,

helicopters and for supersonic airplanes for the issue of a type certificate are prescribed

according to the provisions of Chapter 1 of Annex 16, Volume I, Part II to the Chicago

Convention.

b) The applicable emission requirements for the issue of a type certificate for an aircraft and

engine are prescribed in Annex 16 to the Chicago Convention.

c) EASA shall issue certification specifications providing an acceptable means to demonstrate

compliance with the noise and the emission requirements.

6.10. Changes Requiring a New Type Certificate (EASA Part 21, 21.A.19)

A new application for a type certificate shall be made if the Agency finds that the change in

design, power, thrust, or mass is so extensive that a substantially complete investigation of

compliance with the applicable type certification basis is required.

6.11. Compliance with the Type Certification Basis and Environmental Protection

Requirements (EASA Part 21, 21.A.20)

a) The applicant for a type certificate shall show compliance with the applicable type

certification basis and environmental protection requirements and shall provide the Agency

the means by which such compliance has been demonstrated.

b) The applicant shall provide the Agency with a certification programme detailing the means

of compliance demonstration. This document shall be updated during the certification

process as necessary.

c) The application shall record justification of compliance within compliance documents

according to the certification programme established in point b) above.

d) The applicant shall declare that it has demonstrated compliance with the applicable type

certification basis and environmental protection requirements according to the certification

programme established in point b) above.

6.12. Issue of a Type Certificate (EASA Part21, 21.A.21)

The applicant shall be entitled to have a product type-certificate issues by the Agency after:

a) Demonstrating its capability in accordance with point 21.A.14.

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b) Submitting the declaration referred to in point 21.A.20(d); and

c) It is shown that:

i. The product to be certificated meets the applicable type certification basis and

environmental protection requirements designated in accordance with points 21.A.17

and 21.A.18;

ii. Any airworthiness provisions not complies with are compensated for by factors that

provide and equivalent level of safety;

iii. No feature or characteristic makes it unsafe for the uses for which certification is

requested; and,

iv. The type certificate applicant has expressly stated that it is prepared to comply with

point 21.A.44.

d) In the case of an aircraft type certificate, the engine or propeller, or both, if installed on the

aircraft, have a type certificate issued or determined.

6.13. Issue of a Restricted Type Certificate (EASA Part 21, 21.A.23)

a) For an aircraft that does not meet the provisions of point 21.A.21(c), the applicant shall be

entitled to have a restricted type certificate issues by the Agency after:

i. Complying with the appropriate type certification basis established by the Agency

ensuring adequate safety with regarded to the intended use of the aircraft, and with the

applicable environmental protection requirements;

ii. Expressly stating that it is prepared to comply with point 21.A.44.

b) The engine or propeller installed in the aircraft, or both, shall:

i. Have a type certificate issued;

ii. Have been shown to be in compliance with the certification specifications necessary to

ensure safe flight of the aircraft.

6.14. Type Design (EASA Part 21, 21.A.31)

a) The type design shall consist of:

i. The drawings and specifications, and a listing of those drawings and specifications,

necessary to define the configuration and the design features of the product shown to

comply with the applicable type certification basis and environmental protection

requirements;

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ii. Information on materials and processes and on methods of manufacture and assembly

of the product necessary to ensure the conformity of the product;

iii. An approved airworthiness limitations section of the instructions for continued

airworthiness as defined by the applicable airworthiness code; and

iv. Any other necessary to allow by comparison, the determination of the airworthiness,

the noise characteristics, fuel venting, and exhaust emissions or later products of the

same type.

The type design not only deals with the product configuration but with the production

methods as well. Every deviation from the type design is a change, which must also be

approved. This is to ensure that series products are not inferior to the prototype identified by

the type design [1].

6.15. Inspections and Tests (EASA Part 21, 21.A.33)

a) The applicant shall perform all inspections and tests necessary to demonstrate compliance

with the applicable type certification basis and environmental protection requirements.

b) Before each test required by paragraph a) is undertaken, the applicant shall have

determined:

i. For the test specimen:

That materials and processes conform to the specifications for the proposed type

design;

That parts of the products conform to the drawings in the proposed type design;

That the manufacturing processes, construction and assembly conform to those

specified in the proposed design; and

ii. That the test equipment and all measuring equipment used for tests are adequate for

the test and are adequately calibrated.

c) The applicant shall allow the Agency to make any inspection necessary to check

compliance with paragraph b).

d) The applicant shall allow that Agency to review any report and make any inspection and to

perform and witness any flight and ground test necessary to check the validity of the

declaration of compliance submitted by the applicant under point 21.A.20(d) and to

determine that no feature or characteristic makes the product unsafe for the uses for which

certification is requested.

e) For tests performed or witnessed by the Agency under paragraph d):

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i. The applicant shall submit to the agency a statement of compliance with paragraph b);

and

ii. No change related to the test that would affect the statement of compliance may be

made to a product, part or appliance between the time compliance with paragraph b) is

shown and the time it is presented to the Agency for test.

6.16. Flight Tests (EASA Part 21, 21.A.35)

a) Flight testing for the purpose of obtaining a type certificate shall be conducted in

accordance with conditions for such flight testing by the Agency.

b) The applicant shall make all flight tests that the Agency finds necessary:

i. To determine compliance with the applicable type certification basis and

environmental protection requirements;

ii. To determine whether there is reasonable assurance that the aircraft, its parts and

appliances are reliable and function properly for aircraft to be certified under Part 21,

except for:

Sailplanes and powered sailplanes;

Balloons and airships defined in ELA1 and ELA2;

Airplanes with a maximum take-off mass of 2722 kg or less.

c) The flight tests shall include:

i. For aircraft incorporating turbine engines of a type not previously used in a type

certificated aircraft, at least 300 hours of operation with a full complement of engines

that conform to a type certificate, and

ii. For all other aircraft, at least 150 hours of operation.

6.17. Type Certificate (EASA Part 21, 21.A.41)

The type certificate and restricted type certificate are both considered to include the type

design, the operating limitations, the type certificate data sheet for airworthiness and

emissions, the applicable type certification basis and environmental protection requirements

with which the Agency records compliance, and any other conditions or limitations prescribed

for the product in the applicable certification specifications and environmental protection

requirements. The aircraft type certificate and restricted type certificate both include the type

certificate data sheet for noise.

The engine type certificate data sheet includes the record of emission compliance.

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6.18. Obligations of the Holder (EASA Part21, 21.A.44)

Each holder of a type certificate or restricted type certificate shall continue to meet the

qualification requirements for eligibility under point 21.A.14.

6.19. Transferability (EASA Part21, 21.A.47)

Transfer of a type certificate or a restricted type certificate may only made to a natural or legal

person that is able to undertake the obligations under point 21.A.44 and has demonstrated its

ability to qualify under the criteria of point 21.A.14.

6.20. Duration and Continued Validity (EASA Part21, 21.A.51)

A type certificate and restricted type certificate shall be issued for an unlimited duration

provided that the holder remains in compliance with Part 21 and the certificate is not

surrendered or revoked. Upon surrender or revocation, the type certificate or a restricted type

certificate shall be returned to the Agency.

6.21. Record Keeping (EASA Part 21, 21.A.55)

All relevant design information, drawings and test reports, including inspection records for

the product shall be held by the type certificate or a restricted type certificate holder at the

disposal of the Agency and shall be retained in order to provide the information necessary to

ensure the continued airworthiness and compliance with applicable environmental protection

requirements of the product.

6.22. Manuals (EASA Part 21, 21.A.57)

The holder of a type certificate or a restricted type certificate shall produce, maintain and

update master copies of all manuals required by the applicable type certification basis and

environmental protection requirements for the product.

6.23. Instructions for Continued Airworthiness (EASA Part21, 21.A.61)

a) The holder of the type certificate or a restricted type certificate shall furnish at least one set

of complete instructions for continued airworthiness, comprising descriptive data and

accomplishment instructions prepared in accordance with the applicable type certification

basis, to each known owner of one or more aircraft, engine or propeller upon its delivery or

upon issue of the first certificate of airworthiness for the affected aircraft, whichever

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occurs later. The availability of some manuals or parts of the instructions for continued

airworthiness, dealing with overhaul or other forms of heavy maintenance may be delayed

until after the product has entered into service but shall be available before any of the

products reach the relevant age or flight hours/cycles.

b) In addition, changes to the instructions for continued airworthiness shall be made available

to all known operators of the product and shall be made available on request to any person

required to comply with any of those instructions. A programme showing how changes to

the instructions for continued airworthiness are distributed shall be submitted to the

Agency.

7. Design Requirements and Specifications

Appropriate regulations are outlined in Table 3 for small airplanes, i.e. airplanes that are in

CS/FAR-23 and CS-VLA classification. Table 4 gives a summary of design requirements and

specifications for the same class of airplanes.

Table 3. Certification specifications and applicability.

Category Normal, Utility, Aerobatic Commuter Very Light

Characteristics

Maximum take-off weight (kg/lb)

Number of engines

Type of engine

Maximum number of occupants

Maximum operation altitude (ft)

≤ 5670/12500

1 or 2

All1

≤ 9

25000

≤ 8628/19000

2

Propeller

≤ 19

25000

750

1

Spark or

compression

ignition

0

8000

Applicable Certification Specifications

Airplane

Engines

Propellers

Noise standards

CS/FAR-23

CS-E/FAR-33

CS-P/FAR-35

CS/FAR-36

CS/FAR-23

CS-E/FAR-33

CS-P/FAR-35

CS/FAR-36

CS-VLA2

CS-E

CS-P

- 1 Although there is no explicitly specified restriction, single turbine engine airplanes are

incompatible with the stall speed requirement, see Table 4. 2 An equivalent FAA standard does not exist. FAA adopted CS-VLA for the certification of

very light aeroplanes in the US.

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Table 4. Stall Speed, take-off and landing specifications.

Classification Normal, Utility, Aerobatic Commuter Very Light

Velocity

Stall speed1, VSO2 (km/h / knot)

Rotation speed, VR (single engine)

Rotation speed, VR (twin engine)

Take-off speed, VTO (single engine)

Take-off speed, VTO (multi-engine)

Climb speed, VCL (single engine)

Climb speed, VCL (twin engine, AEO6)

Climb speed, VCL (twin engine, OEI7)

Approach speed, VA

≤ 113/61

≥ VS13

max(1.05VMC4, 1.10VS1)

≥ 1.2VS1

max(1.10VMC, 1.20VS1)

≥ 1.2VS1

max(1.10VMC,1.20VS1)

≥ 1.2VS1

max(VMC, 1.30 VSO)

-

-

max(V15, 1.05VMC, 1.1VS1)

-

max(1.10VMC, 1.20VS1)

-

-

≥ V28

max(1.05VMC, 1.30VSO)

≤ 45/83

-

-

-

-

≥ 1.3VS1

-

-

≥ 1.3VSO

Climb

Climb gradient, γ @ VCL (Wo ≤ 2722 kg, AEO)

Climb gradient, γ @ VCL (Wo ≥ 2722 kg, AEO)

Climb gradient, γ @ VCL (Wo ≤ 2722 kg, VSO ≥ 113 km/h, OEI)

Climb gradient, γ @ VCL (Wo ≤ 2722 kg, VSO ≤ 113 km/h, OEI)

Climb gradient, γ @ VCL (Wo ≥ 2722 kg, OEI)

≥ 8.3 %

≥ 4.0 %

≥ 1.5 %

-

≥ 0.75 %

-

-

-

-

≥ 2.0 %

≥ 2m/s

-

-

-

-

Landing

Descent gradient ≤ 5.2 % - 1 There is no stall speed requirement for twin-engined airplanes provided that the one engine inoperative climb gradient requirement is satisfied. 2 VSO: stall speed in the landing configuration. 3 VS1: stall speed obtained in a specified configuration. In this case, take-off configuration. 4 VMC: minimum control speed with the critical engine inoperative. 5 V1: decision speed. 6 AEO: All engines operating. 7 OEI: One engine inoperative. 8 V2: take-off safety speed.

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References

1. De Florio, F., Airworthiness: An Introduction to Aircraft Certification, Oxford: Elsevier,

2011.

2. http://en.wikipedia.org/wiki/Airworthiness, accessed on 14.03.2014.

3. http://en.wikipedia.org/wiki/National_aviation_authority, accessed on 14.03.2014.

4. van Santen, C.W. Airwortiness Procedures Inplementation Management (Joint Aviation

Authorities), IR 21-Presentation, 2013.

5. European Aviation Safety Agency, Certification Specifications for Very Light Aeroplanes,

CS-VLA, Amendment 1, 2009.

6. European Aviation Safety Agency, Certification Specifications and Acceptable Means of

Compliance for Light Sport Aeroplanes, CS-LSA, Amendment 1, 2013.

7. European Aviation Safety Agency, Certification Specifications for Normal, Utility,

Aerobatic and Commuter category Aeroplanes, CS-23, Amendment 3, 2012.

8. European Aviation Safety Agency, Certification Specifications for Large Aeroplanes,

CS-25, Amendment 14, 2013.

9. http://en.wikipedia.org/wiki/Type_certificate, accessed on 14.03.2014.

10. Airwortiness Procedures Inplementation Management (Joint Aviation Authorities), IR 21-

Annex Part 21, 2013.

11.http://www.skybrary.aero/index.php/Acceptable_Means_of_Compliance_and_Guidance_

Material, accessed on 14.03.2014.