The return of the 737 Max aircraft could be severely delayed if pilots are required to train in flight simulators.
Global airline regulators met last week in Texas to discuss questions surrounding the aircraft’s return.
One of the major questions still unanswered is around whether pilots should be trained on flight stimulators or on iPads, according to The Financial Times.
There is only one flight simulator owned by an airline in the US – Air Canada.
Up until now, the US Federal Aviation Administration (FAA) has stipulated computer-based training would be enough.
The FAA is reviewing an emergency procedure in circumstances similar to the two crashes, which saw the nose of the plane go down in error.
The 737 Max had been grounded since March after two crashes in five months in which 346 people died in crashes in Indonesia and Ethiopia.
US pilots had received only one to three hours of training on an iPad to prepare them to fly the Max before the crashes.
The FAA must decide whether pilots need to be trained in a Max simulator after the faulty manoeuvring system (MCAS) is repaired.
Boeing is understood to have finished a fix but has not yet submitted it to the FAA for approval.
More: Regulator refuses to set timetable for Boeing 737 Max return