by far, with 614 Series 300 aircraft and their subvariants (Series 310 for United Kingdom operators, Series 320 for Australian operators, etc.) sold before production in Toronto by de Havilland Canada ended in 1988. In 1972, its unit cost was US$680,000, In 1976, a new -300 would have cost $700,000 ($ million 31 years later) and is still worth more than $2.5 million in 2018 despite the -400 introduction, many years after the -300 production ceased. New production After Series 300 production ended, the remaining tooling was purchased by Viking Air of Victoria, British Columbia, which manufactures replacement parts for all of the out-of-production de Havilland Canada aircraft. On 24 February 2006, Viking purchased the type certificates from Bombardier Aviation for all the out-of-production de Havilland Canada aircraft (DHC-1 through DHC-7). The ownership of the certificates gives Viking the exclusive right to manufacture new aircraft. On 17 July 2006, at the Farnborough Airshow, Viking Air announced its intention to offer a Series 400 Twin Otter. On 2 April 2007, Viking announced that with 27 orders and options in hand, it was restarting production of the Twin Otter, equipped with more powerful Pratt & Whitney Canada PT6A-34 engines. As of November 2007, 40 firm orders and 10 options had been taken and a new final assembly plant was established in Calgary, Alberta. Zimex Aviation of Switzerland received the first new production aircraft, serial number 845, in July 2010. By mid-2014, Viking had built 55 new aircraft at its Calgary facility. The production rate as of summer 2014 was about 24 aircraft per year. In April 2015, Viking announced a reduction of the production rate to 18 aircraft per year. On 17 June 2015, Viking further announced a partnership with a Chinese firm, Reignwood Aviation Group. The group will purchase 50 aircraft and become the exclusive representatives for new Series 400 Twin Otters in China. Major changes introduced with the Series 400 include Honeywell Primus Apex fully integrated avionics, deletion of the AC electrical system, deletion of the beta backup system, modernization of the electrical and lighting systems, and use of composites for non load-bearing structures such as doors. The 100th Series 400 Twin Otter (MSN 944) was displayed at the July 2017 EAA AirVenture Oshkosh. Currently, 38% are operated as regional airliners, 31% in military aviation or special missions, 26% in industrial support and 5% in private air charter. Additionally, 70