The US aviation regulator has denied a report that the Boeing 737 MAX remains grounded because of fears that women pilots are too weak to operate an emergency lever in the cockpit.

The Federal Aviation Authority (FAA) said the crisis-hit Boeing’s return to service was not being delayed over concerns that pilots with below-average strength would be unable to crank a lever to return the aircraft to a normal position in an emergency.

The Wall Street Journal newspaper reported on Wednesday that the review process had been held up as a result of the issue.

The 737 MAX was grounded across the world three months ago after two fatal crashes in short succession were found to share similarities.

A problem with flight control systems has been identified as a common theme between the crash of a Lion Air flight in Indonesia last October and the loss of an Ethiopian Airlines flight in March.

The issue can be rectified by the use of a manual lever in the cockpit, called a trim wheel, which alters a plane’s angle.

But the trim wheel can require extreme force to operate in certain situations.

The FAA insisted that concerns about pilots’ ability to operate the trim wheel were not behind the delay in re-certifying the 737 MAX.

A spokesperson told the CNBC website pilot strength was an issue the agency was examining, but not one it expected would delay the plane’s return to service.

Boeing has apologised for its handling of a software glitch which affected some flight control elements of the MAX.

It is uncertain when the type will be re-certified for passenger services once more, but Boeing said it was working to do so soon.

The manufacturer received a boost this week after British Airways’ owner, International Airlines Group, announced plans to purchase up to 200 737 MAXes.