SunExpress Germany Boeing 737-800 aircraft landing at Dusseldorf DUS EDDL international airport in Germany. The Boeing 737 airplane has the registration D-ASXR and has two CFM56-7 jet engines.

Leisure airline SunExpress increased its order for Boeing 737 Max planes, delivering a vote of confidence in the jetliners that have been grounded since mid-March after two fatal crashes killed 346 people.

The Antalya, Turkey-based airline exercised options for an additional 10 of the 737 Max 8 planes, worth $1.2 billion at list prices, before routine discounts, Boeing announced on Monday during the Dubai Airshow. SunExpress, a joint venture of Lufthansa and Turkish Airlines that serves destinations throughout Europe and vacation spots around the Mediterranean and Black Sea, had previously ordered 32 of the 737 Max jetliners.

Boeing has struggled this year as it halted deliveries of its fast-selling 737 Max planes and new orders all but dried up in the wake of the crashes. British Airways parent, International Consolidated Airline Group, said during the Paris Airshow in June that it intends to buy 200 of the 737 Max planes, but that order has not been firmed up.

The worldwide grounding has eaten into the profits of airlines with the 737 Max in their fleets and curbed their growth plans.

"We are honored and humbled by the trust that SunExpress has placed in our team at Boeing," Stan Deal, who took over as chief executive of Boeing's all-important commercial aircraft unit last month after the previous CEO was ousted, said in a release. "We regret the impact the Max grounding has had on SunExpress and their passengers."

Boeing has been scrambling to gain regulator approval of software fixes for the planes after a flight-control system was implicated in both crashes, drawing harsh criticism and several investigations about Boeing's design and the Federal Aviation Administration's certification of the planes in 2017.

"We have full confidence that Boeing will deliver us a safe, reliable, and efficient aircraft," said SunExpress CEO Jens Bischof. "However, it goes without saying that this requires the undisputed airworthiness of the model, granted by all relevant authorities. Our utmost priority at SunExpress is and has always been safety."