Introduction

Even to a layperson, it is evident that many different types of aircraft are flying about, including general aviation aircraft, helicopters, commercial airliners, military aircraft, etc., as shown in the exemplary photos below. Besides airplanes, there are lighter-than-air concepts such as airships (i.e., dirigibles and blimps) and balloons, unpowered aircraft such as sailplanes and hang gliders, as well as rotorcraft in the form of helicopters, gyroplanes (autogiros), and tiltrotors. Today, more unoccupied air vehicles or UAVs (drones), which are often classified as powered-lift aircraft, are flying in the airspace and have to safely intermingle with existing aircraft operations. A tiltrotor may also be categorized as a form of powered-lift aircraft.

Aerospace engineers need to become familiar with how types of aircraft are classified and used, e.g., whether it is a civilian or civil airplane designed to transport passengers (i.e., an airliner) or a general aviation airplane intended for training and recreational use or a military aircraft developed for a combat role, or some other type of aviation asset. This distinction is fundamental because the regulations that apply to an aircraft’s engineering design, manufacturing, testing, and flight operations depend on the classification of that aircraft.

Furthermore, aerospace engineers need to understand the specific regulatory requirements that apply to the aircraft they are designing and to stay current with any changes to regulations as they are periodically updated. Therefore, engineers must have a good understanding of the regulations and guidelines. It is also essential for engineers to consider the impact of regulations on their design choices and to balance the safety, performance, and cost requirements. Ultimately, the goal is to produce safe and reliable aircraft that meet a customer’s operational and budgetary requirements while adhering to the regulatory framework.

In practice, aircraft are best classified by using criteria besides just the in-service use of the aircraft, such as the nature of its propulsion system (e.g., propeller or jet), the number of engines (e.g., single-engine or multi-engine), land-based or sea-based, or in some other way such as primarily passenger-carrying or primarily cargo-carrying. In some cases, the classification may be unambiguous. However, in other cases, a precise aircraft classification, such as for certification and the issuance of a Certificate of Airworthiness, may require careful qualification., e.g., for an amphibious aircraft or a tiltrotor. Most aircraft, however, will fall clearly into a defined classification based on their intended purpose and use.

Civil aircraft are formally classified by the U.S. Federal Aviation Administration (FAA) according to categories, classes, and types. For example, one aircraft category is an airplane, and a class of an airplane is a single-engine, land-based airplane, one type being the Cessna 172, as shown in the photograph below. In addition, other classes of airplanes are multi-engine and seaplanes, both of which are different classes of airplanes or “fixed-wing” aircraft.

Multi-engine airplanes and larger aircraft are more complicated from the engineering design perspective and their actual operation. Another category of aircraft is a “rotating-wing” aircraft or rotorcraft, the classes of rotorcraft being a helicopter, a gyroplane (autogiro), or a tiltrotor. A tiltrotor is a rotorcraft concept that combines some elements of a helicopter with some of those of an airplane and falls into the “hybrid” classification as a powered-lift aircraft. There are also many less-common types of aircraft in the aviation spectrum, such as powered parachutes and “weight-shift” controlled aircraft such as hang gliders.

Some form of armed service operates military aircraft, typically one of two types: combat or non-combat aircraft. On the one hand, combat aircraft are designed to attack and destroy enemy equipment using their ordnance or to intercept and render inactive other aircraft, such as fighter aircraft. Fighter aircraft are usually designed to fly fast, perhaps even supersonically, and have good maneuverability and agility.

On the other hand, non-combat military aircraft can include transport aircraft used to move personnel and cargo and aircraft used for pilot training. Military aircraft must meet the same strict safety and performance standards as their civilian counterparts but also must be designed and equipped to perform their mission in a hostile environment and withstand damage. Military aircraft often require specialized features such as armor, defensive systems, and weapons. Additionally, military aircraft must be compatible with military-specific support equipment and infrastructure.

Overview of Aircraft Classifications

The design, operation, and regulations for aircraft vary greatly depending on the aircraft type and its intended use. For example, military aircraft must meet different requirements than commercial airliners, and small general aviation aircraft have different regulations than larger commercial aircraft. Each aircraft type has unique characteristics and operational requirements that must be considered in its design and regulation, so a one-size-fits-all approach is not practical or effective.

Different aircraft types have different operational requirements and must be designed to meet those requirements, which will determine the set of rules and regulations that apply. The aircraft’s size, weight, complexity, intended use, and human factors all play a role in determining the specific regulations and standards that must be met. The regulatory authorities must ensure that the safety of the aircraft and its passengers is guaranteed, which is why the regulations for each type of aircraft can vary widely. More stringent rules will govern larger, heavier, and more complex passenger-carrying aircraft and comprise more complicated requirements. Again, different rules and regulations will necessarily apply to crewed versus uncrewed aircraft design and operation.

Uses of Aircraft

In all the various ways aircraft may be classified, the most prominent and fundamental distinction is whether they are intended for civil or military use. For example, civil airplanes are usually designed to transport passengers or cargo or both, often over very long distances. These larger passenger-carrying types are called airliners, i.e., commercial airplanes used by airlines to carry fare-paying passengers safely and in comfort from one place to another. Therefore, an airliner then becomes one type of aircraft classification to which stringent design rules and operational regulations will necessarily apply, mainly because the safety of all the passengers is paramount.

Smaller civil aircraft types are used in general aviation (GA), a form of private, non-commercial aviation activity. GA includes various aircraft types, such as trainers, gliders, helicopters, homebuilts, and perhaps even retired military aircraft or “warbirds,” etc. The vast majority of civil aircraft in use today are of the GA type. GA aircraft usually have relatively low-speed capabilities and limited range, but some smaller jet-powered business/corporate “biz-jet” aircraft also fit into the GA category. Again, different standards apply to these aircraft types, depending on their exact classification, size, and gross weight.

A military aircraft is operated by the armed services and could be either a combat or non-combat aircraft type. Combat aircraft are designed to carry munitions (e.g., bombs, rockets, etc.) to attack and destroy enemy assets. Combat aircraft are further classified as fighters or bombers, with fighter aircraft being smaller and more agile, and are designed primarily to intercept enemy aircraft and enter into an air-to-air engagement. The aircraft’s high-speed flight capability, maneuverability, and agility are essential. However, there are also many hybrid types of aircraft that are “dual-use” variations of such military aircraft, e.g., fighter/bomber aircraft classifications.

Non-combat aircraft may fulfill many roles, including reconnaissance, transport, in-flight refueling, and search and rescue. Successful non-combat military aircraft have often been derivatives of civil aircraft designs, adapted and modified to meet specific military requirements. For example, the Boeing KC-135 tanker is a derivative of the Boeing 707 but will be replaced by the Boeing KC-46 Pegasus, and the VC-25 or “Air Force One” is a derivative of the Boeing 747. These aircraft versions must typically operate in harsher military conditions compared to what civil aircraft must endure and may need to carry defensive weapons or other systems such as airborne command centers or electronic countermeasures.

Civil Aircraft Types & Classifications

The FAA classifies aircraft according to categories, classes, and types. The primary categories and classes of civil aircraft are:

• Airplanes:
  • Single-engine land (SEL)
  • Multi-engine land (MEL)
  • Single-engine sea (SES)
  • Multi-engine sea (MES)
• Rotorcraft:
  • Helicopter
  • Gyroplane
  • Tiltrotor
• Lighter-than-air or aerostats:
  • Airship (e.g., a blimp or dirigible)
  • Balloon (e.g., a hot-air balloon)
• Glider (or sailplane).

Other aircraft categories include:

• Powered-lift (which may include uncrewed aerial vehicles or UAVs.).
• Powered parachutes:
  • Land operation.
  • Sea operation.
• Weight-shift aircraft (e.g., hang-gliders):
  • Land operation.
  • Sea operation.
• Rockets

Remember that an aircraft’s class refers to the subdivisions within each aircraft category. In the airplane category, a class can refer to either the single-engine land class, the multi-engine land class, the single-engine sea class, or the multi-engine sea class. The aircraft type refers to a specific make and model of aircraft within a given class; e.g., a Boeing 787 or an Airbus A380 would both be a type of airplane in the multi-engine land class.

In the rotorcraft category, a class can be a helicopter, a gyroplane (autogiro), or a tiltrotor. A type of helicopter would be the Sikorsky S-76, and a type of tiltrotor would be the AW609. Notice that a tiltrotor is a rotorcraft and also a form of powered-lift aircraft other than a helicopter. A gyroplane or autogiro may look superficially like a helicopter. However, its main rotor is unpowered, so it only produces lift if the aircraft moves forward and/or downward to spin the rotor. Another type of powered-lift aircraft would use downward thrust from the jet engines to produce the needed lift other than using rotors, e.g., a vertical takeoff and landing (VTOL) aircraft using jet thrust only.

In the lighter-than-air category, the two classes are airship and hot-air balloon; the lift on an airship is produced by buoyancy from the displacement of air by the helium-filled gas envelope. Types of airships are a blimp and a dirigible; the primary difference is that a blimp has a non-rigid gas envelope, whereas a dirigible has its gas envelope supported by a rigid, frame-like internal structure. With some exceptions, both blimps and dirigibles are powered by propellers or ducted fans and steered using a rudder and elevator.

Gliders and sailplanes are relatively simple aircraft because they have no engine (unless classified as a self-launching sailplane) and have few systems, i.e., no hydraulics and no (or limited) electrical systems. A sailplane is typically thought of as a high-performance glider. An example of a weight-shift aircraft would be a hang glider, which has no conventional flight control surfaces and relies on kinesthetic control.

Unoccupied Aircraft

An uncrewed or unoccupied aircraft (UAV) or unoccupied aircraft system (UAS), often called a drone, is an aircraft without a human pilot physically onboard. Instead, an operator on the ground controls the flight of the UAV remotely through a communications link. One or more pilots fly crewed aircraft, but uncrewed or unoccupied aerial vehicles (UAVs) may be flown remotely from a ground-based station or fly autonomously using signals from ground-based sensors. UAS is often used in reference to drones because it emphasizes the importance of elements other than the UAV, which generally include ground-based control systems and support equipment such as a command center.

The FAA defines a UAV as a “powered, aerial vehicle that does not carry a human operator, uses aerodynamic forces to provide vehicle lift, can fly autonomously or be piloted remotely, can be expendable or recoverable, and can carry a lethal or nonlethal payload.” This means that a UAV will generally fall into the powered-lift aircraft category. Small UAVs mostly use lithium-ion (Li-ion) or lithium-polymer batteries (Li-Po) to power electric motors. At the same time, larger UAVs may rely on internal combustion engines or hybrid internal combustion engines and electrical powerplants.

The last decade has seen explosive growth in the use of UAVs for both military and civil applications. As shown in the figure below, the quadcopter design has become a prevalent configuration for smaller UAVs. Most UAVs carry cameras, although other sensor packages may be used too. The relationship of UAVs to radio-controlled model aircraft has become more indistinct; in fact, UAVs may or may now include aircraft previously classified as model aircraft. For example, in the U.S., the FAA defines any uncrewed or unoccupied aircraft as a UAV, regardless of size or weight. However, a radio-controlled aircraft always formally becomes a UAV if it has a flight control system that allows it to fly autonomously.

Aviation & Aeronautical Regulations

The vast scope and complexity of aviation and aeronautical/aerospace engineering are such that standardized regulations are needed to govern the myriad of processes that encompass everything from aircraft design to flight operations and piloting. Regulations are not developed to stifle aeronautical progress but to ensure safety and consistency in aircraft design and operation. Regulations are also needed to guarantee the safety of all related aeronautical and aviation matters and that the general public is adequately protected from unnecessary risks; such regulations also help provide for National security.

In the U.S., the Federal Aviation Regulations (referred to as the “FARs”) are regulations and standards that the FAA publishes; these regulations govern all civil aviation activities. The FAA is the sole authority that the U.S. Government has granted the regulatory and legal powers to regulate all aspects of civil aviation. The FAA technically and legally enforces the FARs, i.e., the FARs carry the force of U.S. law. Therefore, beyond the airworthiness issues and operational requirements governed by the FARs, any violations of the FARs can result in the suspension of FAA licenses or certificates and significant fines or imprisonment for those involved in proven violations.

The FARs were established in 1965 from the existing U.S. Civil Air Regulations. These regulations originally stemmed from the policies established after the formation of the International Civil Aviation Organization (ICAO). The ICAO is an agency of the United Nations and was formed in 1947 after the Chicago Convention of 1944, where the countries of the World came together for a conference in Chicago to discuss the future of civil aviation. The purpose of ICAO is to adopt standards and set policy so that “International civil aviation may be developed in a safe and orderly manner and that international air transport services may be established based on equality of opportunity and operated soundly and economically.”

The ICAO has 191 member states (all of the UN member states) that work with various aviation organizations at all levels to develop international Standards and Recommended Practices (SARPs) for all aspects of civil aviation. In addition, the ICAO ensures that aviation regulations are unified for all member states to ensure uniform design and safety requirements. To this end, the SARPs form the basis for all civil aviation regulations, such as the FARs in the U.S. and the European Aviation Safety Agency (EASA) in Europe.

Most nations of the world have an equivalent to the FAA in the form of a Civil Aviation Authority (CAA), a national regulatory body responsible for all aspects of that nation’s aviation matters. All CAA organizations subscribe to the ICAO SARPs in adopting a broadly accepted aviation policy and setting appropriate legislation to regulate aircraft design and operations. Technically, the ICAO SARP recommendations are not legally binding. However, as previously mentioned, any legal requirements are usually formally embodied in the respective CAA regulations developed by each country, including the FARs in the U.S.

It is important to note that the FAA does not directly regulate any aspect of military aviation, that is, other than overseeing military flight operations in civilian airspace. Nevertheless, military aviation regulations generally parallel the FAR regulations and, in some cases, may be more stringent. However, as previously mentioned, the FAA still publishes design and operational requirements for military aircraft based on commercial designs, which would apply to militarized civil aircraft.

The SARPs also form the basis for many military aviation standards, even though these tend to be less formally structured than the FARs. There are no open publications that discuss military airworthiness standards or procedures. It must be accepted that military aircraft, by design, must be allowed the flexibility to operate with a greater level of risk tolerance than would be permitted with any civil aircraft, not least because they will often need to carry bombs, missiles, etc. Nevertheless, military aircraft are usually designed to meet, if not exceed, all relevant civil airworthiness standards.

Military Aviation Authorities (MAAs) have been formed in many countries, similar to CAAs, and the MAAs adopt regulations underpinned by the ICAO standards and policies. For example, defense standards in the form of military standards MIL-STD or MIL-SPEC (or, informally, “MilSpecs”) flow from the ICAO standards, which are used to help achieve aviation standardization objectives set by the U.S. Department of Defense (DoD). In the U.K., the Military Aviation Authority operates under the auspices of the U.K. Ministry for Defence (noticing that “Defence” is the British spelling of “Defense” in American English).

The EASA is the European Aviation Safety Agency, which was formed in 2002 by the European Commission, and their regulations replaced the Joint Aviation Regulations (JARs) previously established by the European Union (EU) countries. Like all CAAs, EASA formalizes aviation safety, gives technical advice to all EU member states, and awards airworthiness and type certification of civil aircraft. EASA originated in the early 1970s, known as Joint Airworthiness Authorities (JAA). Its objectives are the same as the FAA’s FARs: standardizing certification requirements for large civil aircraft and aircraft engines. Today, EASA fulfills a broader role in aviation and aerospace engineering, governing all of the civil aviation activities in Europe that parallels what the FAA does in the U.S.

Details of the Federal Aviation Regulations

The FARs are formally a part of Title 14 of the Code of Federal Regulations (CFR), which governs “Aeronautics and Space.” The aeronautical FARs can be found online as sections or parts 1 to 199 of the Code of Federal Regulations (e-CFR). Parts 400 to 1199 of the CFR pertain to commercial space operations. While the FARs are technically organized into many parts, not all are currently used, and some parts (mainly the even-numbered parts) have been left open for future use by the FAA. The latter parts of CFR Title 14, namely Parts 1200 to 1299, pertain to NASA operations, and Parts 1300 to 1399, pertain to air transportation system stabilization.

The FARs used to be published in hard copy only, and because they are voluminous, they require a small library to store them all. However, the eFARs under Title 14 are readily available online. The legalistic undertones of the FARs will not go unnoticed by most engineers, perhaps affirming the place of these regulatory documents as part of aviation law.

FARs for Aeronautical Engineers

Some valuable parts of the FARs for aeronautical engineers include (but are not limited to):

• Part 23 – Airworthiness Standards: Normal, Utility, Acrobatic, and Commuter Airplanes.
• Part 25 – Airworthiness Standards: Transport Category Airplanes.
• Part 27 – Airworthiness Standards: Normal Category Rotorcraft.
• Part 29 – Airworthiness Standards: Transport Category Rotorcraft.
• Part 33 – Airworthiness Standards: Aircraft Engines.
• Part 35 – Airworthiness Standards: Propellers.
• Part 39 – Airworthiness Directives.
• Part 91 – General Operating and Flight Rules.
• Part 107 – Small Unmanned (Unoccupied) Aircraft Systems.
• Part 125 – Certification and Operations: Airplanes Having a Seating Capacity of 20 or More Passengers or a Payload Capacity of 6,000 lb (2,721 kg) or More.

Of primary relevance to most aeronautical engineers are FAR Parts 23 and 25, as well as Part 33, which will cover the vast majority of airplanes being designed and built in terms of FAA airworthiness standards. In tis regard, airworthiness can be defined as the ability of an aircraft or other airborne system to operate successfully and safely without significant hazards to aircrew, ground crew, passengers (if relevant), or the general public at large.

Part 23 contains the prescriptive airworthiness standards that must be met for the issuance of a Certificate of Airworthiness to airplanes (referred to as Normal, Utility, Acrobatic, or Commuter Airplanes), and Part 25 refers to Transport Category airplanes (i.e., the larger, passenger-carrying commercial airplanes or airliners). These parts of the FARs also explain how such airworthiness standards are to be imposed and proven to gain a Certificate of Airworthiness. These parts of the FARs are certification regulations developed over many years to ensure that new airplanes are fully airworthy and safe for crew and passengers alike. For example, the relevant regulations in Parts 23 and 25 include standards that govern the structural loads on airframes (in the air and on the ground), all aspects of flight performance, flight stability and control characteristics, gust loads, maneuvering flight, low-speed flight, and stalling characteristics, all types of flight systems, various types of safety mechanisms and emergency procedures, engines, etc.

Obviously, not all airplanes are intended for the same purpose. In addition, some airplanes are more complicated than others, so the regulations do not need to apply uniformly to every type of airplane. For example, a twin-engine turboprop or “commuter” airplane carrying passengers is more complicated than a single-engine, two-seater training airplane regarding its design and operation. Therefore, more stringent standards must be applied to the commuter airplane, and more straightforward regulations would commensurately apply to the training airplane.

To this end, the FAA regulations within Part 23 are subdivided into design and airworthiness regulations that will apply specifically to the type, size, and weight of the airplane, i.e.,

• Airplanes that can carry nine or fewer passengers, the airplane having a gross takeoff weight of up to 12,500 lb (5,670 kg).
• Normal or non-acrobatic operation; “non-acrobatic” is defined that the aircraft’s bank angle during flight must not exceed 60 degrees.
• Utility or limited acrobatic operation in which the bank angle during flight can reach between 60 and 90 degrees.
• Acrobatic use has no bank angle or other flight attitude restrictions and allows unlimited flight maneuvers.
• The commuter category is multi-engine airplanes with 19 or fewer passengers. These aircraft types must have a gross takeoff weight of less than 19,000 lb (8,618 kg).

FAR Part 25 pertains to airworthiness and other standards for airplanes in the transport category. Transport category airplanes are defined as one of the following:

• Jet (turbine) propelled airplanes with ten or more seats or a maximum takeoff weight greater than 12,500 lb (5,670 kg).
• Propeller-driven airplanes with more than 19 seats or a maximum takeoff weight greater than 19,000 lb (8,618 kg), i.e., they do not fall into the commuter category of Part 23.

Like those requirements stated in Part 23, the various regulations cover airframe loads, performance, stability and control, stalling characteristics, engines, etc.

FAR Part 26 (one of the few even-numbered parts) has been added more recently to cover the continued airworthiness standards and safety improvements needed to ensure the continued airworthiness of the larger transport category airplanes, which in some cases are now reaching operational lives that are 40 years old.

FAR Parts 27 and 29 pertain to the rotorcraft airworthiness standards in the normal and transport categories, respectively. The normal category includes rotorcraft up to a maximum takeoff weight of 7,000 lb (3,175 kg). Examples of types in this category would be the Schweizer 300 and the Bell 429 helicopters. For heavier rotorcraft or those carrying ten or more passengers, then Part 29 regulations will apply. As rotorcraft get even bigger and heavier, they need to be held to even higher standards to ensure their airworthiness, so rotorcraft that weigh more than 20,000 lb (9,100 kg) are certified under the so-called “Category A” standards, as defined within the regulations of Part 29.

Certificate of Airworthiness.

The issuance of a Certificate of Airworthiness (or a “C of A”) is a permit for a specific aircraft to fly in the national and international airspace systems. Every aircraft must have its own C of A, an example being shown in the figure below. Generally, granting a Certificate of Airworthiness to an aircraft by an ICAO-recognized certification authority will also allow that aircraft to be flown in the airspace of any ICAO member state. The Certificate of Airworthiness is, in effect, the “graduation diploma” for an aircraft, and it proves that the aircraft has successfully met or exceeded the standard of the various tests imposed as part of the standards.

Most of the documentation and other evidence needed to gain a Certificate of Airworthiness is obtained through flight testing, although a substantial amount of ground testing is usually required too. For example, most structural tests are better carried out on the ground, where loads can be applied in a controlled manner, and engineers can make detailed measurements of structural deformations and material strains. Some tests, such as cabin pressurization tests and specific engine tests, are unsafe to conduct in the air, so they are done on the ground under more controlled conditions. Demonstrations of engine performance can also be better monitored on the ground, including tests such as water and bird ingestion and different types of prescribed failures.

An airworthiness certificate remains valid as long as the aircraft meets its approved type design and is in a condition for safe operation through maintenance and preventative maintenance under the FARs. The registration mark (in box 1) is unique to the aircraft, with a prefix designating the country in which the aircraft is certified. The prefix “N” is used for US-registered aircraft. Other examples are “C” for Canada, “F” for France, “D” for Germany, and “G” for Great Britain.

In the FARs, the FAA uses the name “category” as both a category of aircraft (for piloting) and a category of function (for certification). The designations “Transport, Commuter, Normal, Utility, or Aerobatic (in box 4) are endorsements on the certificate of airworthiness based on the certified (design) function of an aircraft, e.g., airplane, even though these functions are often called categories for pilot certification. Other category endorsements include Limited, Experimental, Restricted, Provisional, Light-Sport, or Primary. However, aircraft categories and classes are still used to denote different types of aircraft for both design and piloting. An airplane is still an airplane regardless, but it could be one of the airworthiness designations,  e.g., an airplane with a “Transport” function, so hence the rules appear under aircraft/airplane/transport. Likewise, single-engine versus multi-engine land/sea are important class designations because different rules apply both to design and piloting.

A summary of the certification categories is as follows:

• Transport: An aircraft with varying seating and weight criteria based on engine type, with jet engine, transports rated for more than 10 seats and over 12,500 pounds, and piston engine transports capable of carrying up to 19 people and weighing more than 19,000 pounds.
• Commuter: A multi-engine propeller aircraft for transporting up to 19 passengers, with a weight limit under 19,000 pounds.
• Normal: An aircraft not approved for aerobatic flight, with a capacity of 9 or fewer passengers and a maximum takeoff weight of 12,500 pounds.
• Utility: An aircraft with a maximum of 9 passenger seats plus pilot seats, weighing up to 12,500 pounds, and authorized for limited aerobatic maneuvers.
• Aerobatic: An aircraft capable of performing aerobatic flight with limited restrictions, with a maximum of 9 seats plus the pilot and a weight limit of 12,500 pounds.
• Limited: A category for military aircraft modified or converted for civil use.
• Experimental: A category covering various aircraft, including kit-built, amateur-built, unoccupied, light sport, research and development, and air racing projects.
• Restricted: A category for aircraft built for specific purposes, such as agriculture, conservation, surveying, weather control, or advertising, which can only be used for their designated purpose.
• Provisional: A category for aircraft that is only certified for a limited duration, e.g., one year.
• Light Sport (LSA): A sport aircraft category that does not fall under the gyroplane, kit-built, or ultralight categories.
• Primary: A category for aircraft manufactured with a production certificate and intended for personal use. Carrying persons or property for hire is generally prohibited for this category.

Not all aircraft will have, or even need to have, a Certificate of Airworthiness and can be operated in the “Experimental” category. This category would be for an aircraft that is either not yet certified but is undergoing certification testing (i.e., a temporary classification) or amateur or kit-built and will remain forever in the “Experimental” category. The construction of amateur and kit-built aircraft is overseen by the Experimental Aircraft Association (EAA).

Other Airworthiness Documents

As previously discussed, the primary airworthiness document is a Certificate of Airworthiness, the permit to fly as a certified aircraft. The Certificate of Airworthiness must be carried and displayed in the aircraft when operating. Other documentation relevant to aircraft design, maintenance, flight operations, and safety can be found in the FAA’s Regulatory & Guidance Library (RGL), which is now known as the Dynamic Regulatory System which is a “Comprehensive Knowledge Center of Regulatory and Guidance Material from the Office of Aviation Safety and other Services and Offices.” Documents to be found there include:

• Advisory Circulars (ACs).
• Airworthiness Directives (ADs).
• Lists of Supplemental Type Certificates (STCs).
• Lists of Parts Manufacturer Approval (PMA).
• Legacy certification regulations are used as reference materials.

While ACs contain essential information regarding the aspects of the given aircraft, compliance is purely advisory. ADs require mandatory compliance from the owner/operator of the aircraft to maintain airworthiness and carry the lawful force of the FARs. Maintenance to comply with an AD must be documented or otherwise recorded in the aircraft logs. Remember that non-compliance with the FARs may result in legal consequences, including fines or even imprisonment for egregious violations that result in a loss of life or well-being. These documents can also be found on the FAA’s RGL website.

The aircraft manufacturers themselves may also issue airworthiness documentation. Service Bulletins (SBs) help alert aircraft owners and operators to potential airworthiness issues. SBs are usually about minor issues and often preventative maintenance matters (e.g., corrosion concerns or minor fatigue cracking) that are less likely to develop into something more severe if not taken care of as part of routine maintenance. Only commercial aircraft operators are required to comply with all SB notifications. However, most private non-commercial operators will still adhere to the manufacturer’s airworthiness recommendations as part of the aircraft’s standard maintenance protocols, relieving the operator from liability if an incident or mishap is tied to the SB issue.

Regulations for Unoccupied Aircraft & Drones

An uncrewed or unoccupied aircraft (UAV) or uncrewed or unoccupied system (UAS), which is sometimes called a “drone,” is an aircraft without a human pilot physically onboard the aircraft. Part 107 of the FARs covers a broad spectrum of commercial uses for drones weighing less than 55 lb (24.9 kg). The FAA introduced these regulations recently because of the proliferation of various commercially available drones, some of which were being flown high and fast enough to pose a danger to other aviation operations or the general public. While Part 107 rules are flexible enough to accommodate future technological innovations, they also impose restrictions on the operations of all types of drones for safety considerations. FAR Part 107 sets down a series of “common sense” rules requiring a drone operator to avoid all kinds of crewed aircraft and never operate such a drone carelessly or recklessly.

For now, with some exceptions, such unoccupied aircraft must be flown within line of sight, i.e., the operator must be able to see the drone at all times with the naked eye or “unaided sight,” so the use of binoculars is prohibited. In addition, the drone’s maximum allowable altitude is 400 ft (122 m) above the ground or higher if flown within 400 ft (122 m) of a structure, and its maximum allowable airspeed is 100 mph (161 kph). Finally, notice that the FAA still considers a UAV or a drone to be an aircraft because the FAA’s definition of an aircraft includes any “contrivance” that flies, contrary to definitions that others may use.

A remote pilot airman certificate is required to operate the controls of a UAS, UAV, or drone under FAR Part 107. The FAA does not require an aircraft in this category to comply with any airworthiness standards, nor does the aircraft have to comply with any certification standards. Instead, FAR Part 107 requires visual and operational pre-flight checks to ensure the drone’s flight and flight safety systems are “functioning properly.” The FAA also requires a UAS, a UAV, or some other drone to be available for inspection or testing on request, so records must be maintained. Because these parts of the FARs also carry the force of U.S. law, the failure of an owner or operator of a drone to comply with the requirements of Part 107, even unintentionally, could expose them to fines or other civil penalties.

Regulations for Commercial Space Operations

Spacecraft come in many types, shapes, and sizes, including single-stage and multi-stage rockets, reusable spacecraft, satellites, and interplanetary probes. Commercial space and launch vehicles are manufactured and marketed by private companies. Several companies are currently developing orbital and suborbital vehicles to be used for a variety of missions, including space tourism. The recent launches of space tourists on the Virgin Galactic and Blue Origin spacecraft suggest that commercial space activities will become increasingly common in the coming decades. However, these vehicles are not formally classified as aircraft for design or operational purposes.

The regulatory responsibility for the commercial space industry comes under the jurisdiction of the FAA and the Office of Commercial Space Transportation (AST), which is a part of the FAA. However, the FAA does not regulate any spacecraft launches undertaken by U.S. government organizations, e.g., NASA. In this regard, the FAA defines a commercial spacecraft launch as one of the following:

• The FAA has licensed the launch.
• The launch contract for the primary payload was open to international competition.
• The launch was privately financed without any government support.

The FAA’s commercial space transportation regulations are in Parts 400 to 460 of CFR Title 14.

• Part 401 – General Requirements: This part outlines general requirements for launch and reentry activities, including licensing procedures, financial responsibility, and safety.
• Part 415 – Launch Safety: Covers safety requirements for launch and reentry operations to protect the public and property.
• Part 417 – Launch Safety: Provides specific requirements for launch safety analysis and criteria.
• Part 431 – Launch and Reentry of a Reusable Launch Vehicle (RLV): Pertains to the licensing of reusable launch vehicles.
• Part 435 – Reentry of a Reentry Vehicle Other Than a Reusable Launch Vehicle (RLV): Addresses the licensing of reentry vehicles.
• Part 440 – Financial Responsibility: Outlines the financial responsibility requirements for launch and reentry operators.
• Part 460 – Licensing and Safety Requirements for Launch: Regulations for obtaining a license for commercial space launch and reentry operations.

Summary & Closure

Aviation is a highly regulated activity, and for a good reason, safety is always paramount. Uniformity of standards requires that regulations be applied to the design and testing of aircraft as well as to piloting and all aspects of flight operations. The International Civil Aviation Organization (ICAO) sets standards and adopts policies for civil aviation, but the actual regulation and enforcement of these standards are left to individual countries. Because the same regulations cannot (and need not) be applied uniformly to all aircraft types, specific regulations pertaining to different categories and classes of aircraft are developed. This includes regulations for aircraft design, testing, piloting, and flight operations, ensuring aviation safety. These regulations are essential to ensure consistent and uniform standards for aviation globally.

Most countries have a Civil Aviation Authority (CAA), which in the U.S. is the FAA, and these CAAs oversee all aspects of civil aviation. They are responsible for setting and enforcing regulations to ensure the safe operation of civil aviation within their jurisdiction. These regulations are essential to ensure uniformity and consistency in aircraft design, operations, and maintenance and to promote high safety for passengers, crew, and the general public. The regulations are regularly reviewed and updated to reflect technological advances, operational practice changes, and emerging safety concerns.