United Airlines allegedly used a plane that was 'not in an airworthy condition' for 23 flights, and could now be fined $435,000.

The carrier repaired a fuel pump pressure switch on a Boeing 787 on June 9, 2014, the Federal Aviation Administration said on Tuesday.

But United flew the plane on domestic and international routes before carrying out the required inspection of the new switch 21 days later on June 28.

The FAA said the airline even used the plane on two flights after being warned they skipped the inspection.

It is the latest controversy the beleaguered airline has faced in the last two months.

United Airlines allegedly used a plane that was 'not in an airworthy condition' for 23 flights and could now be fined $435,000 (file photo)

It started in April with the video of Dr Dao being aggressively dragged off a flight, and was followed by the mysterious death of a giant rabbit in a plane's cargo hold.

The airline can appeal the proposed penalty.

A spokesman for Chicago-based United says the airline 'immediately took action' after identifying the issue and is working with the FAA.

'At United, the safety of our customers and employees is our top priority,' they said.

An FAA administrator said: 'Maintaining the highest levels of safety depends on operators closely following all applicable rules and regulations.

'Failing to do so can create unsafe conditions.'

There is no indication the failure to inspect the replaced switch caused a problem on any of the 23 flights United made.

In April, United suffered extreme global backlash after a video surfaced — and immediately went viral — showing cops violently dragging a bleeding Dr. David Dao off of an overbooked United Flight 3411 from Chicago to Louisville, Kentucky

The airline has faced a number of catastrophic PR disasters this year in regards to its treatment of passengers.

Most recently, United apologized to Henry Amador-Batten, a gay father, who was flying with his son to their North Carolina home last Saturday.

Flight attendants on the United flight from Newark to Raleigh-Durham accused Amador-Batten of inappropriately touching his son.

The attendants told police they saw a male passenger with his hands resting 'near the genitals' of a boy, according to CNN.

The 53-year-old father was then questioned by police once the flight landed.

He told authorities that his son was afraid of flying and that he had his hand on the boy's lap to help him feel secure and go to sleep, according to CNN.

'This is not how anyone deserves to be treated,' Amador-Batten's husband, Joel, wrote in a Facebook post for their gay parenting blog DADsquared.

'This is not something that should have happened in front of my son. This is not something that anyone should have to worry about happening to them on a flight just because someone might not like the looks of them,' the post read.

Amador-Batten and his husband called the incident 'mean-spirited and co

Florida-based attorney, Kenneth Padowitz, who is representing the Amador-Batten family, told CNN he was considering filing a lawsuit against United over their 'outrageous conduct', adding that the public is 'sick and tired of being treated like this by airlines'.

In a statement to CNN, United apologized for the incident calling it a 'misunderstanding'.

In April, United suffered extreme global backlash after a video surfaced — and immediately went viral — showing cops violently dragging a bleeding Dr. David Dao off of an overbooked United Flight 3411 from Chicago to Louisville, Kentucky.

Simon, a three foot long and black-furred bunny (pictured), was expected to become the largest rabbit in the world. He died after he was flown to Chicago from London

Dao had refused to leave the plane on his own after claiming that he needed to return to Louisville because he had patients waiting for him.

While being removed from the plane, Dao broke his nose, lost two teeth and suffered a concussion. He has since settled with the airline for an undisclosed amount.

The airline has since settled a suit brought by Dr Dao, for an undisclosed amount.

Less than three weeks after Dao's airplane trauma, United experienced another public relations nightmare when it was revealed that a three-foot-long rabbit died in one of their airplane's cargo holds during a flight from London to Chicago.

The circumstances leading to the continental giant rabbit's death have not been revealed yet.

Earlier this month, passengers reported being attacked by a scorpion that caused a flight to evacuate.