By Ankit Ajmera and Tim Hepher

DUBAI (Reuters) - Boeing Co <BA.N> won fresh support for its grounded 737 MAX at the Dubai Airshow on Tuesday as airlines laid out plans to buy up to 50 of the jets worth $6 billion at list prices, a day after securing the first firm order since a safety ban in March.

Kazakhstan flag carrier Air Astana said it had signed a letter of intent to order 30 Boeing 737 MAX 8 jets for its recently launched FlyArystan low-cost subsidiary.

Such draft deals can take time to turn into final contracts but the signing gave embattled Boeing a public boost as it faces concerns over increased regulatory scrutiny following two fatal accidents that led to the eight-month-old grounding.

"We are confident in Boeing's professionalism to overcome interim technical difficulties," Air Astana Chief Planning Officer Alma Aliguzhinova told reporters when asked about the decision to back the MAX.

But the U.S. planemaker's chances of finalizing a separate deal for 40 787 Dreamliners at the show hung in the balance as delegates reported tough negotiations with host carrier Emirates and official state business slowed.

The United Arab Emirates declared three days of mourning late on Monday following the death of the president’s representative and brother, Sheikh Khalifa bin Zayed al-Nahyan.

Local radio stations canceled their planned programming in line with traditions when the country is in mourning and no music was being played at the air show on Tuesday.

However, Emirates late on Tuesday scheduled an air show news conference for 0700 GMT on Wednesday. No further details were immediately available.

Global regulators halted commercial flights of Boeing's popular 737 MAX jet in March after two fatal accidents.

Plans for the jet's return to commercial service have been pushed back to early 2020 as Boeing finalizes software and training revisions that need regulatory approval.

Air Astana intends to hold 15 of the proposed Boeing 737 MAX aircraft directly and may finance the rest through a lease transaction, Aliguzhinova said, adding that it would not change the composition of its main fleet including Airbus jets.

Separately, an unnamed airline signed a firm order for 10 Boeing 737 MAX 7s and 10 Boeing MAX 10 jets, a person familiar with the matter said.

AFRICA GROWTH

Elsewhere at the largest Middle East air event, Saudi budget airline Flynas agreed to buy 10 long-range A321XLR jets after Reuters reported it aimed to expand its Airbus <AIR.PA> fleet.

In deals involving Africa, which is trying to liberalize its skies to win back regional traffic from Middle East carriers, Airbus unveiled a provisional order for eight of its small A220 jets from Air Senegal, while Ghana's government provisionally ordered three Boeing 787 to help set up a new home-based carrier.

Leasing giant GECAS confirmed a new order for 25 Airbus planes including 12 A330neo, first reported by Reuters, as well as plans to convert another seven aircraft to a different model.

The order involves a potentially key endorsement for the Rolls-Royce-powered A330neo from the affiliate of a rival engine maker, and continues the diversification of GECAS's portfolio from mainly General Electric Co <GE.N> engines under a recently renewed management.

Airbus has had mixed fortunes on the aircraft in recent weeks as Emirates dropped plans to order the A330neo while expanding an order for newer A350s and the U.S Federal Aviation Administration downgraded Malaysia, in a move that analysts said could hit plans by AirAsia to fly A330neos to the United States.

Emirates President Tim Clark confirmed on Tuesday that it had not ruled out looking at the A330neo at a later date.

The fate of the A30neo at Emirates is in part linked to whether the airline has a place for the competing Boeing 787-10.

(Reporting by Ankit Ajmera and Tim Hepher; Additional reporting by Alexander Cornwell, Stanley Carvalho; Editing by David Goodman and Lisa Shumaker)