Boeing and Alaska Airlines have finalised the order for 23 737-9 MAX aircraft as part of the US carrier’s fleet modernisation programme.

The confirmation comes three months after Alaska Airlines revealed its plans to buy the additional aircraft.

According to the agreement, Boeing will deliver the 23 MAX 9 aircraft to Alaska Airlines between 2023 and 2024. The jets will be modified to a three-class configuration with 178 seats.

The order includes 15 options that are slated to be delivered between 2023 and 2026.

With this deal, Alaska has boosted its order book of 737 MAX, including options and lease commitments at 120 aeroplanes.

The carrier took the delivery of its first 737-9 in January and has already deployed it to revenue service on 1 March.

The second 737-9 entered service on 18 March and two additional 737-9s are scheduled to begin revenue service next week.

The purchase of new aircraft will allow the carrier to move to an all-Boeing mainline fleet, enhance efficiency and sustainability across its operations.

The Boeing 737-9 features fuel-efficient engines and updated aerodynamics, which reduces fuel usage by 20% and emissions by 20% per seat compared with the aircraft the jet replaces.

Earlier this week, another US carrier Southwest Airlines placed an order for 100 Boeing 737 MAX jets following a multi-year evaluation to modernise its fleet.

Temporarily grounded for nearly two years, the Boeing 737 MAX was finally ungrounded last November.

In December, European carrier Ryanair signed a purchase agreement with Boeing for 75 new MAX-8200 aircraft.