Boeing booked 30 orders for 737 MAX jets Tuesday at the Dubai Airshow, a vote of confidence in the aircraft following its worldwide grounding in March.

Kazakhstan's Air Astana signed a letter of intent to purchase the MAX planes, valued at about $3.6 billion, Boeing announced.

"We believe the MAX will provide a solid platform for growth once the aircraft has successfully returned to service," Peter Foster, the airline's CEO, said in a statement. "We believe the efficiency and reliability built into the 737 MAX will be a great fit. Air Astana has had a strong relationship with Boeing ever since the airline started flying in 2002 with a pair of 737 NGs."

The Wall Street Journal, citing a person familiar with the agreement, said Boeing also signed a deal Tuesday for 20 MAX jets with an undisclosed customer, boosting total sales at the Dubai Airshow to about $6 billion.

On Monday, Boeing booked a $1.2 billion order for 10 additional 737 MAX jets from SunExpress, a Turkish carrier linking Europe and Turkey with holiday destinations, adding to the carrier's previous order for 32, Boeing said.

"We have full confidence that Boeing will deliver a safe, reliable and efficient aircraft, SunExpress CEO Jens Bischof said in a statement. "However, it goes without saying that this requires the undisputed airworthiness of the model granted by all relevant authorities."

The 737 MAX, Boeing's top-selling plane, has been grounded since March after crashes in Indonesia and Ethiopia killed all 346 passengers and crew on board. Investigators believe the MAX's automated anti-stall device, called the Maneuvering Characteristics Augmentation System (MCAS), erroneously pointed the nose of the planes down to avoid a midair stall and into a fatal plunge.

China was the first country to ground the MAX; the US was the last. Boeing has updated the anti-stall software, but the FAA has not yet approved it.

At the Paris Air Show in June, International Consolidated Airlines Group, owner of several airlines, including British Airways, Aer Lingus and Iberia, announced a deal for 200 MAX jets.

The deal has yet to be completed, but analysts viewed it as a vote of confidence in Boeing. MAX jets list for about $120 million each, but the value of the announced deals do not include any discounts and are estimates.

At the Dubai Airshow, Airbus, Boeing's European competitor, announced a $14 billion order from Air Arabia for 120 single-aisle A320neos. The MAX and neo are twin engine, fuel-efficient planes designed for short-to-medium trips.

The Journal reported that production limitations have prevented Airbus from taking full advantage of Boeing's troubles because the European plane builder has booked all production slots for the A320neo until 2024.

Boeing has parked newly built but undelivered MAXs. Orders for the MAX are expected to increase when the plane has been cleared to return to commercial service.