On Wednesday The Wall Street Journal reported that the re-certification of 737 Max planes had been held up, in part, over the plane’s manual crank, which angles the plane’s nose, and can require extreme force to operate in certain situations.

The US Federal Aviation Authority (FAA) does not agree with claims that the re-certification of Boeing's embattled grounded 737 Max planes is being held up over concerns that pilots might lack the physical strength to turn an emergency crank on the plane. A spokesperson told CNBC website that pilot strength was an issue the agency was looking into, but not one that might delay the plane’s return to service.

On Wednesday The Wall Street Journal wrote the review process for the 737 Max was reportedly being hampered, in part, over the plane’s trim wheel system, a manual crank that turns a horizontal panel on the aircraft’s tail to change the angle of the plane’s nose and which can require extreme force to operate in certain situations.

Sources had claimed, according to the WSJ, that there were concerns whether the average pilot would have the physical strength to return the aircraft to a normal position in an emergency.

Internal debates regarding the issue, claimed the sources, could lead to a delay in getting the 737 Max jets back up in the air.

There were concerns, allegedly, about whether female pilots would have the brute force to manage the crank, while the sources ruled out plans to using strength characteristics as a factor which would prevent certain pilots from flying the passenger jets.

This news comes as a congressional hearing on Wednesday was attended by US-based pilots demanding enhanced pilot training on the Max jets prior to the aircraft being returned to service.

The pilots, including Chesley 'Sully' Sullenberger III, pushed back against the aviation giant's assurances that pilots will only need to review the 737 MAX modifications in a computer program.

Daniel Carey, president of the Allied Pilots Association, told a congressional panel he was encouraged by changes Boeing made to its flight system, which was seen as a factor in both the Lion Air and Ethiopian Airlines crashes that killed 346 people.

But the American Airlines captain expressed concerns that training being discussed by the manufacturer would be insufficient.

“We remained concerned about whether the new training protocol, materials and method of instruction suggested by Boeing are adequate to ensure the pilots across the globe flying the MAX fleet can do so in absolute complete safety,” Carey told the House committee.

The computer-based program used previously in training was not sufficient, said another pilot present at the hearings, Chesley 'Sully' Sullenberger III, as he demanded simulator training for MAX pilots.

He emphasised that pilots must develop muscle memory of their reactions in different trouble-shooting situations.

However, a flight simulator training requirement would involve thousands of pilots and likely extend the time needed for flights to resume.

© AP Photo / Ted S. Warren Boeing 737 MAX 8

The third hearing in Congress since the 737 MAX grounding comes as Boeing continues its work with the US Federal Aviation Administration and other regulators in a desperate bid to re-certify the plane and get it back in the skies in 2019.

Boeing insists it is making progress on getting its fixes for the troubled jet approved, but has stopped giving any public estimates about when that approval might come.

The global Max fleet was grounded in March following two fatal crashes. An Ethiopian Airlines 737 Max 8 plane crashed after takeoff, killing all 157 passengers and crew on board. That crash came just five months after the October 2018 crash of a Lion Air 737 Max 8, which killed all 189 people on board.

A malfunction of the plane’s automated flight-control system, called MCAS, was implicated.