Boeing’s grounded airliners are likely to be parked longer now that European and Canadian regulators plan to conduct their own reviews of changes the company is making after two of the jets crashed.

The Europeans and Canadians want to do more than simply take the U.S. Federal Aviation Administration’s word that alterations to a key flight-control system will make the 737 Max safer. Those reviews scramble an ambitious schedule set by Boeing and could undercut the FAA’s reputation around the world.

Boeing hopes by Monday to finish an update to software that can automatically point the nose of the plane sharply downward in some circumstances to avoid an aerodynamic stall, according to two people briefed on FAA presentations to congressional committees.

The FAA expects to certify Boeing’s modifications and plans for pilot training in April or May, one of the people said.

Both spoke on the condition of anonymity because they were not authorized to speak about the briefings.

But there are clear doubts about meeting that timetable. Air Canada plans to remove the Boeing 737 Max from its schedule at least through July 1 and suspend some routes that it flew with the plane before it was grounded around the world last week.

American Airlines, Southwest Airlines and United Airlines, which are slightly less dependent on the Max than Air Canada, are juggling their fleets to fill in for grounded planes, but those carriers have still canceled some flights.