The Sk 60E machines were eventually used as Sk 60D liaison transports. Sk 60W In 1993, another upgrade program was initiated to modernize the Sk 60, the most important improvement being fit of twin Williams Rolls FJ44 turbofans with 8.45 kN (861 kgp/1,900 lbf) each and digital engine controls. The new engines not only provide more thrust, but are quieter, cleaner, and easier to maintain. The first Williams-powered Sk 60—known informally as the "Sk 60(W)"—performed its initial flight in August 1995. A total of about 115 conversions of Sk 60A, 60B, and 60C aircraft were performed in the late 1990s. No conversions were performed of the Sk 60D/E, with all such aircraft grounded and used as spares hulks. Saab 105XT Export demonstrator; improved version of the Sk 60B, re-engined with 12.68 kN (2,850 lbf) General Electric J85 turbojets. Prototype converted from second Saab 105 prototype. Saab 105D A refined business jet variant was considered, but the idea was out of date and there were no takers. Saab 105G Revised version of 105XT with new avionics, including precision nav/attack system, more powerful J85 engines and modified wing. One converted from 105 XT prototype. Saab 105H Proposed version for the Swiss Air Force. Never built. Saab 105Ö Variant of the 105XT for the Austrian Air Force, first delivered to Austria in July 1970. 40 built, delivered 1970–72, replacing the de Havilland Vampire and Saab 29 Tunnan. Saab 105S In the mid-1970s, Saab proposed yet another demonstrator, the "Saab 105S" for a Finnish trainer requirement, but the Finns decided to buy the BAe Hawk instead. Operators Austria Austrian Air Force: 40. All retired on 31st of December 2020 after 50 years of service Sweden Swedish Air Force: 72. Specifications (Saab 105Ö) See also References Citations Bibliography Allport, Dave. "Austria Retires Saab 105s". Air International, February 2021, Vol. 100, No. 2. p. 11. Chant, Christopher. A Compendium of Armaments and Military Hardware. London: Routledge, 2014. . Eliasson, Gunnar. Advanced Public Procurement as Industrial Policy: The Aircraft Industry as a Technical University. Springer Science & Business Media, 2010. . Hewson, Robert. "Saab 105/Sk60 Variant Briefing". World Air Power Journal, Volume 23 Winter 1995. London:Aerospace Publishing. . ISSN 0959-7050. pp. 40–49. Phillips, Almarin and A. Paul Phillips, Thomas R. Phillips. Biz Jets: Technology and Market Structure in the Corporate Jet Aircraft Industry. Springer Science & Business Media, 2012. . Michell, Simon (ed.) Jane's Civil and Military