SEATTLE (Reuters) -Boeing ( BA ) expects to finish certification of its best-selling 737 MAX family by the end of the year, CEO Kelly Ortberg said in an interview with trade publication Aviation Week published on Wednesday. 

The company has been trying for several years to gain certification for the smallest and largest MAX variants from the U.S. Federal Aviation Administration. The MAX 7 and MAX 10 have been delayed in part due to concerns with the engine de-icing system.

Ortberg told Aviation Week that the U.S. planemaker hopes to finish certification this year, clearing the way to start deliveries of the MAX 7 and MAX 10, "two airplanes that are very, very important to our customers and our backlog."

Boeing's ( BA ) backlog includes nearly 1,200 orders for the 737 MAX 10 and 332 orders for the MAX 7. 

United Airlines Chief Commercial Officer Andrew Nocella this month told reporters that the company does not expect to take delivery of MAX 10s until 2027 at the earliest. Alaska Airlines officials have said they do not expect to receive the variant until at least mid-2026.

Ortberg also said in the Aviation Week interview that Boeing ( BA ) was making progress on certifying the 777-9, the company's largest jetliner in production. 

When the program was announced in 2013, Boeing ( BA ) planned to start deliveries in 2020. However, it is still in flight testing. Ortberg has previously said publicly that he expects deliveries to start next year.

Boeing ( BA ) has 419 orders for the 777-9, according to its website.