Boeing has decided to temporarily suspend test flights of its new 737 MAX plane due to possible issues with the engine.

The stoppage came days before Boeing was due to make its first delivery of 737 MAX to a customer.

However, Boeing said it was sticking with plans to begin MAX deliveries this month, adding that production of the jets would continue.

American Airlines, Southwest, and China’s Shandong Airlines are among those who have placed orders.

Earlier this year Indian airline SpiceJet placed an order for 205 new planes from Boeing, in a deal valued around $22 billion. Boeing had said the first of the 737 MAX planes would be delivered to SpiceJet in 2018.

The MAX fleet is designed to be a more fuel-efficient version and replaces Boeing’s previous 737 model which has been a best-seller for the aerospace giant.

Boeing says it was notified last week of a potential issue involving turbine engine discs manufactured by a supplier to CFM International.

CFM is the joint venture between General Electric (GE) and French-based Safran – the companies making the engines for the 737 MAX fleet.

Boeing says it has not experienced any problems with the discs during more than 2,000 hours of testing.

The 737 MAX 8, the first version of the plane to be built, carries a list price of $110 million but airlines generally receive steep discounts.

The next model, the 737 MAX 9, has more seating capacity. That aircraft completed a successful maiden flight last month.

Sales and profits slipped at Boeing in 2016, mainly due to lower deliveries of its military aircraft.

Boeing celebrated its 100th year in business in 2016.