A recorded conversation with air traffic control detailed the final moments of the flight, CEO Tewolde GebreMariam told CNN’s Richard Quest on Tuesday.”He was having difficulties with the flight control of the airplane, so he asked to return back to base,” GebreMariam said. He added that the pilot was granted permission to return to ground. That happened at the same time the flight disappeared from radar. All 157 people aboard the Boeing (BA) 737 MAX 8 died when it crashed soon after takeoff from Addis Ababa on Sunday. It was the second time in less than six months that a 737 MAX 8 was involved in a fatal incident, after a Lion Air flight from Indonesia went down in October. GebreMariam said the Ethiopian Airlines pilots had received additional training on the flight procedures involving the 737 MAX 8 after the Lion Air crash. “We believe the similarities are substantial” between the two crashes, GebreMariam said, adding that both incidents featured new models of the same airplane, and both flights lasted only minutes before the planes went down. Both crashes are still under investigation, and there is no evidence that they are linked in causality.GebreMariam declined to say whether he thought all Boeing 737 MAX 8 aircraft should be grounded across the globe, though he noted that Ethiopian Airlines has grounded its fleet of MAX 8s. He also pointed out that several countries, including China, Australia and the United Kingdom, are not allowing MAX 8s to fly either. “We don’t yet know the exact cause of the accident, and speculation is not helpful in either way,” GebreMariam said, “but I think there are questions without answers on the airplane.”The black boxes from the Ethiopian Airlines plane have been recovered, which will enable investigators to learn more about the cause of the crash.GebreMariam said Ethiopia’s Ministry of Transport will work with the United States, where Boeing is based, to find a place to examine that data. Ethiopia does not nave the necessary equipment to perform those tasks on its own, he added.