What is a "small airplane?"
14 CFR part 1 defines a small aircraft as an aircraft of 12,500 lbs or less maximum certificated take-off weight.  Therefore, any airplane, including transport category airplanes, could be considered small by the Part 1 definition if the airplane is less than 12,500 lbs.  

However, as commonly used, and in the most basic sense, small airplanes have generally been considered fixed wing aircraft that are not transport category airplanes (that is, fixed wing airplanes type certificated to standards other than 14 CFR part 25 ).  Therefore, for the purposes of this site, small airplanes are fixed wing airplanes that are not transport category.  Depending on the category, small airplanes can reach up to 19,000 lbs maximum takeoff weight.

Is a small airplane the same as a General Aviation aircraft?
No.  General aviation aircraft are aircraft operated under 14 CFR part 91 rules, which could be any category of airplane, including transport category and rotorcraft.  Additionally, airplanes operated under 14 CFR parts121 and 135, which may include small airplanes, are not considered General Aviation aircraft when operated under these rules.

My airplane meets 14 CFR part 25 (transport category) requirements.  Does this mean I can assume it will meet small airplane (14 CFR part 23) requirements?
No.  The applicable design standards are based upon the type and operation of the airplane.  For example, differences in items such as pilot training and minimum aircrew requirements may result in more stringent flight deck design standards in 14 CFR part 23 airplanes than part 25.  Therefore, the applicable requirements for each category of airplane should be reviewed separately.

More Questions & Answers About Small Airplanes (PDF) –

• Cockpit Controls
• Flight Controls
• Fuels
• Icing Protection Systems
• Landing Gear
• Lights
• Normal, Utility, & Acrobatic Airplanes
• Powerplant
  • Controls
  • Cooling Systems
  • Fire Protection
  • Foreign Object Ingestion
  • Oil Systems
  • Operability
  • Propellers
  • Reversing Systems
  • Subpart E
• Pressurization
• Recording Systems
• Software
• Very Light Airplanes