Saab conceived the 105 in the late 1950s and early 1960s without a firm requirement to build to. The company reasoned that Sweden would soon need to replace its Vampire trainers and that a nimble twin-jet might also find civil buyers as an executive or liaison aircraft. The civil market never materialised, but the military bet paid off spectacularly: Sweden ordered the type, Austria became an export customer, and the aircraft was continually adapted — attack, reconnaissance, liaison and, in the 1990s, a complete new engine. What began as a speculative side-project became one of Saab’s most enduring products, serving for the better part of six decades.

Tandem seating — student in front, instructor behind — was the norm for jet trainers, and it survives on the Hawk and Alpha Jet today. Saab chose a side-by-side layout instead. The advantage is pedagogical: an instructor sitting next to the student can see exactly where the student is looking, what the hands are doing and which instruments are being scanned, and can intervene more naturally. The wide fuselage that made this possible also gave the aircraft a genuine second life as a four-seat liaison and staff-transport machine — simply remove the ejection seats and add passenger chairs. The trade-off is a slightly wider, draggier fuselage than a slim tandem trainer, but for a subsonic multirole jet that mattered little.

By the early 1990s the Saab 105’s original Turboméca Aubisque turbofans were reaching the end of their supportable life — parts were scarce and running costs were climbing. Rather than retire the airframe, Sweden signed a contract (commonly dated to November 1993) to re-engine the fleet with the Williams FJ44, a clean-sheet small turbofan originally developed for business jets. Around 96 aircraft were converted to Sk 60W standard, with re-deliveries running from about 1996; budget cuts had trimmed the programme from an original plan of roughly 115. The FJ44 was lighter, far more fuel-efficient, quieter and cleaner, and delivered a little more thrust. It is the single main reason the Sk 60 was still flying front-line training sorties in the 2020s. (Programme dates vary slightly between sources; treat them as approximate.)

The Saab 105 was procured mainly by two national air forces under state contracts, and no consistent public flyaway unit price or cost-per-flight-hour figure exists for it in open sources. What is documented is the logic of its economics: the whole point of the 1990s Williams FJ44 re-engining was to cut running and maintenance costs, and Sweden judged the upgraded Sk 60 cheap enough to keep flying basic training for another two decades rather than buy a new type. Any precise dollar figure attached to a Saab 105 should be treated as an estimate.