A number of government regulations affect the aerodynamic design of airplanes. The goal is to ensure safe flight. The government is not interested in sacrificing safety for improved economics. For example, the second segment climb requirement described below often determines the engine thrust requirement for twin-engine transports. Other examples include reserve fuel requirements, emergency exits, and flight in icing conditions.

The specific safety-related regulations for commercial aircraft are made in the US by the Federal Aviation Administration (FAA) and have been known as the Federal Aviation Regulations (FARs) from 1958 onwards. However, FAR is also an acronym for “Federal Acquisition Regulations,” and this has led to confusion at times. To avoid this confusion, the term “14 CFR” has been formally adopted for the Federal Aviation Regulations. The United States Code of Federal Regulations (CFR), Title 14, contains rules and regulations issued by the US Department of Transportation and Federal Aviation Administration for Aeronautics and Space, hence the term “14 CFR.” These regulations can be found online in the Code of Federal Regulations, or eCFR, at the following URL: https://www.ecfr.gov/current/title-14. As an example, Part 25, Subchapter C, Chapter I contains Airworthiness Standards for Transport Category Airplanes: https://www.ecfr.gov/current/title-14/chapter-I/subchapter-C/part-25. Examples of regulations include the takeoff and landing distances, engine-out performance, noise limits, icing performance, and emergency evacuation to name a few.

In Europe, the equivalent Joint Aviation Requirements (JARs) are managed by Joint Aviation Authorities and by the European Union Aviation Safety Agency (EASA). Military aircraft also have numerous requirements. In both situations, the emphasis is on safety, including the handling qualities.

Note that many aerospace engineers continue to use the term FAR when referencing the 14 CFR regulations. You should be aware that this is the case with the material in this appendix that was initially prepared when FAR was a much more widely used and accepted term.

The interpretation of the requirements is often complicated. The summary given in this appendix is based on summaries given in appendix F in the aircraft design books by Raymer,^[1] Torenbeek,^[2] and Roskam.^[3] Table C-1 summarizes the various FAR Parts that most directly influence configuration aerodynamics work. The specific requirements depend on the particular type of airplane.

Table C-1: FAR parts directly applicable to design. (*Formerly Part 135; from Torenbeek, then Raymer, p. 803)

Table C-2: Categorizing aircraft—FAA criteria synopsis

With the type of airplane defined above, the various requirements are summarized in the following tables.

Table C-3 defines takeoff requirements, and table C-4 defines the so-called “balanced field length” requirement. For early design studies, the balanced field length is usually determined without allowing for a stop way past the end of runway.

Table C-3: Takeoff requirements

Table C-5 defines the second segment climb and the associated one-engine inoperative (OEI) requirement, which applies to climbs from 35 feet to 400 feet above ground level for engine failure at V₂, the airspeed at the 35-feet height point, with flaps in the takeoff position and landing gear retracted. Note that V₂ > 1.2 Vs in takeoff configuration or V₂ > 1.1 V_mc where V_mc represents the minimum control speed in the engine-out condition.

Table C-5: Second segment climb requirement

Table C-6 defines the requirements for landing, which are similar to the takeoff requirements. Table C-7 defines the requirements for a missed approach. Table C-8 defines typical reserve fuel requirements used in design. Note that the ATA standards are actually more rigorous than the FARs. Table C-9 provides a brief summary of the stability and control issues. In certifying an airplane, the stability and control requirements and handling quality requirements are extremely rigorous and are becoming more so with every accident that occurs on existing airplanes.

Table C-6: CTOL landing requirements

Table C-7: Missed approach requirement

You must carefully examine FAR Part 25 (https://www.ecfr.gov/current/title-14/chapter-I/subchapter-C/part-25) for more complete requirements.

C.1 Light Sport Aircraft (LSA)

Another category of aircraft are now governed by the FAA. Light sport aircraft are intended to make it easier for people to fly airplanes for fun. These aircraft have much simpler, but restrictive, certification requirements. In particular, the max stall speed is 45 kts (52 mph). The maximum weight is 1,320 pounds for land-based airplanes and 1,430 pounds for seaplanes (although several companies seem to have gotten waivers to allow for slightly higher weights). See https://www.ecfr.gov/current/title-14/chapter-I/subchapter-C/part-23 for more details.