The 737 Max has been grounded since March 2019 following two fatal crashes in the space of five months, killing 346 people.
Boeing has been working for the best part of two years on a software fix for the aircraft, as well as new pilot training.
It has been provisionally approved for a return to service in the US, and made its first test flight with non-technical or Boeing passengers onboard – mainly media – on Thursday (3 December).
Ryanair already had 125 737 Maxs on order when the aircraft was grounded, and has now increased its order to 210, with the order now worth in excess of $22 billion (£16 billion).
Following certification by the US Federal Aviation Administration last month, Ryanair said on Thursday it expects deliveries to start early next year and continue over a four-year period to December 2024.
It plans to use the newer, more fuel-efficient aircraft to phase out some of the older aircraft in its fleet, and grow its its network "into new EU countries and markets".
There is yet no firm indication from the European Aviation Safety Agency (Easa) of when it may certify the aircraft as being safe to return to service in Europe.
Ryanair said it had agreed compensation with Boeing for costs incurred over the past 18 months owing to delivery delays, and that some of this had been factored into a "modest reduction" in the cost of the aircraft – enough to "encourage" Ryanair to up its order.
The budget carrier said the aircraft would be "the most audited and most regulated" aircraft in aviation industry.
Features lauded by Ryanair include an additional eight seats per flight, with the aircraft offering 197 in total; a 16% decrease in fuel consumption; and 40% lower noise profile.
"It is the perfect platform to allow Ryanair to expand and grow its low fare services across Europe over the next decade," said the airline. "This new Boeing order helps Ryanair lower its cost base and return to growth across Europe in 2021."
Michael O’Leary, Ryanair group chief executive, said Ryanair expected to take delivery of 50 737 Maxs in 2021. "We will use these new aircraft to replace some of our older Boeing fleet, which will remain grounded until pre-Covid demand returns.
"As soon as the Covid-19 virus recedes – and it will in 2021 with the rollout of multiple effective vaccines – Ryanair and our partner airports across Europe will, with these environmentally efficient aircraft, rapidly restore flights and schedules, recover lost traffic and help the nations of Europe recover their tourism industry, and get young people back to work across the cities, beaches, and ski resorts of the EU."
