The European Aviation Safety Agency (EASA) has addressed its letter to Boeing executives and the corresponding U.S. watchdog, the Federal Aviation Administration, the sources claimed. According to FT, some issues are already being solved, but “not yet all to its satisfaction.”

The key issues reportedly include a software problem in the flight control system, as well as the problems with the trim wheel in the cockpit and autopilot malfunctions. EASA also addressed the failure of the angle of attack sensors in both 737 Max's that have recently crashed.

Boeing declined to comment on the matter. Still, the company has revealed that it is working closely with the regulators to ensure a safe return to service for the 737 Max.

In October 2018, 737 MAX 8 that belonged to the Indonesian airline Lion Air has crashed into the Java Sea 13 minutes after takeoff. All 189 people on board died in the accident. This March, another 737 MAX 8, this time performing an Ethiopian Airlines flight, crashed approximately six minutes after takeoff, taking the lives of 157 people.

After being involved in two fatal accidents, 737 MAX flights were temporarily suspended, resulting in the grounding of a total of 387 aeroplanes. If Boeing is able to resolve all issues by the deadline, the troubled plane could be back by October 2019. However, some experts believe that it is unlikely to happen before 2020.