United Airlines has taken delivery of its first Boeing 737 MAX-family aircraft, a 737-9, and confirmed plans to start service with the newest Boeing narrowbody twinjets in early June.

The Chicago-based carrier, which has 161 737 MAX-family aircraft on order, expects to take delivery of three 737-9s in April and six before the aircraft enters scheduled service on June 7. It will have 10 737-9s by year-end, meaning the aircraft will make up nearly half of the 24 planned additions to the carrier’s mainline fleet in 2018.

Initial 737-9 routes will connect United’s Houston’s George Bush Intercontinental Airport hub and five cities: Anchorage, Alaska; Austin, Texas; Fort Lauderdale and Orlando, Florida; and San Diego, California. The Anchorage service marks the return of a seasonal route. Additional 737-9 flights will begin June 29.

United’s 737-9s are configured with 179 seats, including in 20 first-class and 44 in economy plus. Like the carrier’s 787s, the 737 MAXs will feature a special livery the airline said is intended to emphasize its eco-friendliness.

Meanwhile, United said its Polaris business-class rollout will see a retrofitted aircraft join the fleet about once every 10 days through 2020. The carrier announced Polaris in mid-2016, including a new business-class cabin, onboard service and lounges. Production delays at seat-manufacturer Zodiac Aerospace have delayed United’s retrofit plans.

Sean Broderick, sean.broderick@aviationweek.com