COLOGNE, Germany, Oct 21 (Reuters) - European regulators expect to clear Boeing's grounded 737 MAX to return to service in January at the earliest, following flight trials by European test pilots currently scheduled for mid-December, Europe's top air safety official told Reuters.
The head of the European Union Aviation Safety Agency (EASA) declined to estimate when U.S. regulators would make their own decision to lift a flight ban imposed in March, but said any gap between the agencies would be a matter of weeks not months.
Boeing has said it aims to return the jet to service by year-end following changes to cockpit software and training in the wake of two fatal crashes that sparked the grounding in March.
The U.S. Federal Aviation Administration has primary responsibility for lifting the ban and is expected to be followed by other regulators including EASA, but there have been concerns that other agencies could be slow to act.
"For me it is going to be the beginning of next year, if everything goes well. As far as we know today, we have planned for our flight tests to take place in mid-December which means decisions on a return to service for January, on our side," EASA executive director Patrick Ky said late on Friday.
He said a return to service of the MAX would be coordinated with the FAA as much as possible, but that the two agencies had slightly different processes and consultation requirements.
"So we may end up with a couple of weeks of time difference but we are not talking about six months; we are talking about a delay which, if it happens, will be due mostly to process or administrative technicalities," Ky added.
Ky was speaking shortly before the disclosure on Friday of internal pilot messages from 2016 plunged Boeing into fresh turmoil. On Monday, he declined comment on the messages.
Analysts and unions said the messages could further delay a return to service, but FAA officials said following the release they did not expect the messages would affect tentative plans including a certification flight in early November. The FAA says it needs at least 30 days from then to end the grounding. A European source said there were no immediate signs of an impact.
However, the timing for ungrounding the MAX is not set in stone and depends on a number of outstanding checks.
Ky said the next few weeks would be "critical" as regulators turn their attention to "human factors" - or assessing whether crew can cope with a high workload from future sensor failures. (Reporting by Tim Hepher Editing by Geert De Clercq)