Part 23 versus Part 25 Aircraft, What's the Difference?

Part 23 is the FAA design and certification standard for general aviation aircraft, mostly singles, light twins and some turboprop aircraft. As the low end of the aircraft performance spectrum, Part 23 aircraft have less stringent design standards than those certified to Part 25 standards. Part 25 applies to commercial aircraft, mostly airliners and newer business jets. Because commercial aircraft carry the general public for hire, the wisdom of the FAA stipulates that such aircraft should be designed and be able to perform at a higher level of safety.

The primary differences between the two design standards include the ability of multi-engine Part 25 aircraft to takeoff and climb after one engine fails late in the takeoff roll. Most Part 23 multi-engine aircraft, by comparison, are essentially like single-engine aircraft after one engine fails. Unless they are at very light takeoff weight, the ability to climb after an engine failure on takeoff is mostly non-existent. Like a single-engine aircraft, a twin-engine Part 23 aircraft that has suffered an engine failure on takeoff must essentially make a controlled descent to an emergency landing in all but the most ideal conditions. High density altitude, high gross weight or mishandling by the pilot may make it impossible for a Part 23 aircraft to climb after an engine failure on takeoff.

Another important enhanced safety feature of Part 25 aircraft is the increased system redundancy. Flight instruments, hydraulic systems, navigation equipment and flight controls are just some of the important aircraft systems that are required to retain some operational capability after single or even multiple failures so that the aircraft can continue flying and ultimately land safely.

Part 25 aircraft are also required to have design enhancements that allow continued safe flight after certain structural failures that would make a Part 23 aircraft unairworthy. G-loading tolerances are just one of the differences between the two aircraft design standards.

Flight testing during initial and subsequent certification is also much more involved for Part 25 aircraft. They are required to demonstrate "typical" flight operations capabilities before being approved to carry passengers. Route proving flights, flight in known icing tests and passenger evacuation demonstrations are a few of the additional certification tests required of Part 25 aircraft.

For obvious reasons, the time and effort required to design, built, test and certify a Part 25 aircraft is much more extensive and expensive than for a Part 23 aircraft. The increased complexity of the aircraft makes the Part 25 aircraft much more expensive to purchase and maintain than a Part 23 aircraft. That increased cost and complexity is intended to offer a much safer and more capable aircraft.