No intention of thread-jacking here, but I found this somewhere on the net some time ago and kept it, as I found it quite educational, especially the FAR 23 versus FAR 25 certification. I hope others might appreciate it also.
EDIT:
*I mentioned that I found this on the web some time ago. I wanted to give credit where it is due. The "history" portion of this post is an excerpt of an article written by Fred George of B&CA, whom I had the pleasure to meet at NBAA in 2006. It is from the November, 2002 issue of Business & Commercial Aviation. I highly recommend it if you aren't already a subscriber.
http://tbm700.com/modules.php?name=N...le=print&sid=7
The History of Single-Pilot Citations
Cessna Aircraft earned FAR Part 25 transport category type certification for its Citation 500 fanjet in September 1971 and for its Model 550 Citation II in March 1978. Part 25 aircraft must have at least two crewmembers in the cockpit because of the need to have a back-up in the event of crew incapacitation. The pilot-in-command must have an aircraft type-rating, but the second-in-command need only meet the requirements of Part 61.55.
In 1977, Cessna elected to pursue Part 23 normal category certification for a slightly modified version called the Model 501. Under the requirements of Part 23, aircraft with MTOWs less than 12,500 pounds could be OK’d for single-pilot operations if an FAA evaluation deemed the workload acceptable. The Citation 501, or Citation I/SP, easily passed the FAA’s single-pilot workload test. The pilot-in-command still needed a type rating, but a properly qualified PIC no longer needed an SIC.
For the Citation II, Cessna elected to pursue both Part 25 transport category certification for the basic Model 550, having a 13,300-pound MTOW, and Part 23 normal category certification for the Model 551 Citation II/SP, a 12,500-pound MTOW limited aircraft.
The development of the 14,700-pound MTOW Citation S/II in the early 1980s, though, made it impractical to spin off a 12,500-pound Part 23 version without incurring severe operational limitations. So, Cessna petitioned FAA Flight Standards in Washington, D.C., for an operational exemption to Part 25’s requirement to have two crewmembers, arguing that the excellent safety records of the Citation I/SP and II/SP enabled the S/II to be flown safely by a single pilot with a CE500 common type-rating. The FAA agreed, at the time, and granted what has become known colloquially as the Cessna Exemption. Cessna subsequently applied for extensions of the single-pilot operation exemption for the Citation 500, 550 and 560 models for pilots with the CE500 common type-rating, thus eliminating the need for separate single-pilot, Part 23 versions of 500-series aircraft. Uvalde, Texas-based Sierra Industries and Seattle-based Shannon Engineering also earned single-pilot operational exemptions for Part 25 500-series Citations.
When Cessna initiated development of the Model 525 CitationJet in the late 1980s, though, the FAA determined that it was sufficiently different from other Citation 500 models to warrant a separate type-rating. The CJ would be certified as a Part 23 aircraft, making it eligible for single-pilot operations. Cessna, though, pursued both CE-525 two-pilot and CE-525S single-pilot type-rating approvals, thereby giving operators a choice of flying alone or with an SIC. The CJ3 also will be certified as a Part 23 aircraft, but in the higher-weight commuter category. Want to fly with an SIC if you have a CE-525S type-rating? Just take a Part 61.58 checkride with an SIC and you’re qualified!
Citation Development History
*Citation I: enhanced performance version of the Citation 500, introduced 1976. Compared to the Citation 500, the wingspan was longer, higher gross operating weight, and more powerful JT15D-1A engines.
*Citation I/SP: Special performance version of the Citation I (previously dubbed the Citation 501), introduced in 1977. Last production version of the orignal Citation, last one delivered in 1985. Replaced by the CitationJet. The I/SP is certified for single-pilot operation, but the I and 500 are not.
*Citation II: development of the Citation I originally designated the Citation 550, featuring a fuselage stretch (max seating of 10), longer span wings, more powerful JT15D-4 engines, and increase baggage storage capacity. Certified in 1978.
*Citation II/SP: single-pilot version of the Citation II.
*Citation S/II: based on the Citation II but certified for single-pilot operation, The S/II featured aerodynamic improvements with a new supercritical wing based on what had been developed for the Citation III, and newer JT15D-4B engines. Certified in 1984 and temporarily replaced the Citation II in production until 1985 when the Citation II was reintroduced.
*Citation Bravo: based on the Citation S/II, but with newer PW530A engines, modern cockpit avionics (the Honeywell Primus suite), redesigned interior based on the Citation Ultra, and trailing link main landing gear legs. Certified in 1996, replaced both the Citation II and S/II in production. Current production standard that replaces the I/II series.
*Citation V: development of the Citation I, previously designated Citation 560. The Citation V series is a development of the Citation II/SP. Compared to the Citation II and II/SP, the V series have a slight fuselage stretch and more powerful JT15 engines. The Citation V was certified in 1988.
*Citation Ultra: based on the Citation V with more advanced avionics featuring the Honeywell Primus suite. The Ultra was certified in 1994. Also features an advanced supercritical wing based on the design work for the S/II and Bravo series.
*Citation Ultra Encore: an Ultra with new trailing link main landing gear legs, new fuel efficient PW535 engines, increased fuel payload, redesigned interior and improved systems. Current production standard of the V series.
*Citation III: Originally the Citation 650, the III is larger all-new design to supplement the smaller Citation I/II/V series. Features a swept supercritical wing, T-tail, new fuselage, and Garrett TFE731 turbofans. Certified in 1982.
*Citation VI: low-cost derivative of the Citation III with a standard interior (no customization options) and simpler cockpit avionics. Only 39 were built 1991-1995.
*Citation VII: certified in 1992, the Citation VII is a Citation III with systems improvements and more powerful Garrett engines for better hot/high performance. The VII is still in production, replacing the III/VI series.
*Citation X: Cessna's flagship business jet (designated the 750) first certified in 1996. All new fuselage, sharply swept supercritical wings, FADEC-equipped Allison AE3007 engines, and whole host aerodynamic features to facilitate its high cruise speed. The achievements of the Citation X were so significant, the engineering and test team was awarded the Collier Trophy in 1997.
*Citation X/SP: increased performance version of the Citation X upcoming that will enhance primarily its range/fuel burn.
*Citation Excel: the Model 560 combines a shortened version of the Citation X's fuselage with the advanced supercritical straight wings of the Citation Ultra and new PW545 engines. Certified in 1998.
*Citation Sovereign: the Model 680 features a stretched Excel fuselage combined with all-new supercritical wing with, along with the horizontal tailplane, features a new planform. Uses the PW306 (same engines as on the 329JET).
*CitationJet: The Model 525 replaces the orignal I/II series with the same forward fuselage with an all new wing, new Williams FJ44 engines, and a T-tail. EFIS avionics are standard, as is single-pilot operation. Certified in 1993.
*CitationJet CJ1: A CitationJet 525 with Collins Pro Line 21 cockpit avionics suite and an increased operational gross weight (primarily fuel/payload).
*CitationJet CJ2: stretched CJ1 with more powerful FJ44-2C engines, longer span wings, increased area tail.
*CitationJet CJ3: further stretch of the CJ2 with even longer wings, larger tail, and FADEC controls on more powerful FJ44 engines.
*Citation Mustang: all new light jet aircraft to compete with the likes of the Eclipse 500, smallest of the Citation family past or present. High aspect ratio supercritical wings, T-tail, and sleek contours and oval windows compared the rest of the Citation family.
*CitationJet CJ4: the Citation CJ4 isn’t just another derivative of the CitationJet line, but rather is a clean-sheet design that incorporates some of the best features found in other Citations. It has the Encore-plus’s cockpit and cabin, the Mustang’s wide cabin door, Sovereign-style wing performance and the CJ3’s external baggage capacity. The CJ3 will probably replace the Encore/Encore+ (CE-560) series around 2010, thus ending the Part 25 Cessna Citation 500 series aircraft production run after nearly 40 years.