the Avro RJ100. On long missions, the CS100 was up to 1% more fuel efficient than the brochure and the CS300 up to 3%. The CS300 burned 20% less fuel than the Airbus A319, 21% less than the 737 Classic while the CS100 18 to 27% less per seat than the Avro RJ. The CS300 is lighter than the Airbus A319neo and nearly lighter than the Boeing 737 MAX 7, helping it to achieve up to 12% operating costs savings. 2017 After 28,000 engine hours in 14 in-service aircraft with a powerplant dispatch reliability of 99.9%, Swiss replaced an engine pair in May 2017 after 2,400 hours, while AirBaltic replaced another one in June. Swiss initially flew six sectors a day and by July 2017 up to nine a day with an average time of 1 hours 15 minutes. Air Baltic's flight length averaged 3 hours, and the average fleet daily usage was 14 hours. In September 2017, over 1.5 million passengers had 16,000 revenue flights in the 18 aircraft in service, making up to 100 revenue flights per day on 100 routes: most used were up to 17 hours per day and up to 10 legs per day. Thirty-five minute turnarounds allowed 11 legs per day. On 8 August 2017, following the steep approach certification by EASA, Swiss completed its first revenue flight to London City from Zurich, replacing the Avro RJ. As of September 2017, the CSeries fleet had undergone 20 A Checks with no significant maintenance issues. On 22 December 2017, after months of engine delivery delays, Korean Air became the third airline to take delivery of a CSeries. On 20 January 2018, Korean Air made their first revenue flight with the CS300, from Seoul to Ulsan. Korean Air received its second in early January 2018 and the remaining eight aircraft were to be delivered later in 2018. As of June 2018, Air Baltic reached a maximum utilisation of 18.5 hours a day. A220 2018 On 1 July 2018, the partnership came into effect and the first aircraft with Airbus branding, an A220-300 (former CS300), was delivered to airBaltic on 20 July 2018. On 26 October 2018, Delta Air Lines received its first A220-100 (former CS100) of its order for 75, which was previously disputed by Boeing. On 7 February 2019, Delta operated its maiden A220-100 flight with service from New York–LaGuardia Airport to Dallas–Fort Worth. On