Cessna Citation II

===Upgrades===
By December 2006, Clifford Development in Ohio had launched a program to re-engine Citation IIs with {{cvt|3,000|lbf|kN}} [[Williams FJ44]]-3 engines for $1.9 million (~${{Format price|{{Inflation|index=US-GDP|value=1900000|start_year=2006}}}} in {{Inflation/year|US-GDP}}).<ref name=AIN11dec2006/>
Clifford expected a [[supplemental type certificate|STC]] within 12 months, 21% faster long-range cruise, 29% longer range, 34% better single-engine climb rate and 20% better fuel efficiency.<ref name=AIN11dec2006>{{cite news |url= https://www.ainonline.com/aviation-news/aviation-international-news/2006-12-11/citation-ii-williams-fj44-3-re-engine-stc-works |title= Citation II Williams FJ44-3 re-engine STC in the works |author= Gordon Gilbert |date=December 11, 2006 |work= AIN online}}</ref>
By May 2007, Sierra Industries in Texas was also developing a similar modification, as 900 Citations qualify for it, directly as a broker and [[Maintenance, repair and operations|MRO]] provider, while Clifford should license its STC.<ref>{{cite news |url= https://www.ainonline.com/aviation-news/aviation-international-news/2007-05-30/mod-firms-give-citation-ii-more-power |title= Mod firms give Citation II more power |author= Ian J. Twombly |date=May 30, 2007 |work= AIN online}}</ref>

In September 2008, the FAA granted a STC to Sierra Industries.<ref>{{cite news |date=September 22, 2008 |title= STC'd: FAA Gives 'The Nod' To FJ44-3A-Powered Sierra Super II |url= http://www.aero-news.net/index.cfm?do=main.textpost&id=9d6ff085-4977-4a69-97f2-fb88885ba641 |work= Aero-News Network}}</ref>
The Super S-II made its first flight on September 26.<ref>{{cite news |url= https://www.flightglobal.com/nbaa-2008-sierra-mod-helps-citation-sii-achieve-full-potenital/83287.article |title= NBAA 2008: Sierra mod helps Citation SII 'achieve full potenital' |date= 7 October 2008 |work= flightglobal}}</ref>
The conversion cost $1.9 million in 2009, resulting in a $3.5-4.6 million value for a converted Citation II.<ref name=Flying14apr2009/>
Ceiling is increased from FL 410 to FL 430, reached directly in 25 min at max takeoff weight with a thrust increased from {{cvt|2,500 to 2,820|lbf|kN}} each.<ref name=Flying14apr2009/>
Dual-channel [[full authority digital engine control|FADEC]] allows a much lower residual thrust, eliminating the need for [[thrust reverser]]s.<ref name=Flying14apr2009/>
Max fuel [[payload]] is bumped from {{cvt|328 to 1,278|lb}} for the Citation II, and the S-II can carry {{cvt|400|lb}} more than the initial {{cvt|1,036|lb}}.<ref name=Flying14apr2009/>

Cruise speeds are faster by {{cvt|45 to 400|kn|km/h}} for the 550, and by {{cvt|35 to 420|kn|km/h}} for the Citation S-II.<ref name=Flying14apr2009/>
The converted 550 is 25% more fuel efficient than the JT15D-powered original at the same speed, and burns {{cvt|775|lb}} of fuel per hour at {{cvt|390|kn|km/h}}.<ref name=Flying14apr2009/>
The 550 Range is improved by {{cvt|397 to 1,775|nmi|km}}, and by {{cvt|461 to 2,300|nmi|km}} for the S550.<ref name=Flying14apr2009>{{cite news |url= https://www.flyingmag.com/gear/mods/refurbish/citation-iis-sierra-style/ |title= Citation IIs Sierra Style |work= Flying magazine |author= Robert Goyer |date= April 14, 2009}}</ref>
The re-engined S550 can reach {{cvt|446|kn|km/h}} at FL270.<ref>{{cite news |url= https://www.aopa.org/news-and-media/all-news/2010/march/01/thrust-buster-sierra-super-s-ii |title= Thrust buster: Sierra Super S-II |date=March 1, 2010 |author=Thomas A. Horne |publisher= Aircraft Owners and Pilots Association}}</ref>
Clifford and its partner Stevens Aviation could also update the flight deck with [[Collins Aerospace|Collins]] ProLine 21 avionics and refurbish the cabin.<ref>{{cite news |url= https://www.avbuyer.com/articles/jet-maintenance/inside-maintenance-citation-upgrades-20750 |title= Inside maintenance - Citation Upgrades |author= Dave Higdon |date=June 1, 2011 |work= AvBuyer}}</ref>
Clifford was touting a 14% faster optimum cruise speed, and a 32% lower fuel burn for the S550.<ref>{{cite web |url= http://www.clifforddevelopmentgroup.com/S550Brochure.pdf |archive-url= https://web.archive.org/web/20100816063609if_/http://www.clifforddevelopmentgroup.com/S550Brochure.pdf |url-status= dead |archive-date= 2010-08-16 |title= S550 brochure |publisher= Clifford Development }}</ref>
Sierra was announcing a {{cvt|1,890 and 2,064|nmi|km}} [[Instrument flight rules|IFR]]/[[Visual flight rules|VFR]] range for the re-engined Super II; or a {{cvt|2,340 and 2,610|nmi|km}} IFR/VFR range for the re-engined Super S-II.<ref>{{cite web |url= http://www.sijet.com/download/SIJET_Catalog_2013-14_ALL.pdf |archive-url= https://web.archive.org/web/20160405075028if_/http://www.sijet.com/download/SIJET_Catalog_2013-14_ALL.pdf |url-status= dead |archive-date= 2016-04-05 |title= Catalog |publisher= Sierra Industries |date= 2013}}</ref>
By June 2012, Sierra Industries had re-engined 59 various Citations with FJ44s, among avionics retrofit and airframe modifications.<ref>{{cite news |date=June 20, 2012 |title= Sierra Industries Sets New Delivery Records For Modified Citation Aircraft |url= http://www.aero-news.net/index.cfm?do=main.textpost&id=f0396154-21a7-4794-a8e3-6cec414f9741 |work= Aero-News Network}}</ref>