The problems started when Eagles, who flew with the airline since 2011, entered the cockpit for a flight to Taichung and noticed the captain and the other pilot chatting in Portuguese.

"I said, look guys, I need to start preparing now. Do you mind speaking in English? The captain came around to me and said he was sick of my attitude, sick of me trying to be the captain," Eagles said, adding that it was the first time he had flown with this particular crew.

"Then he threw the clipboard at me. At that moment I said I'd had enough. It's not safe to fly."

Eagles was replaced by another pilot and went to meet the airline's general manager for flying at its Tung Chung offices. He was told he was grounded, pending investigation.

"After the flight, [the manager] asked the senior purser, who witnessed everything. She backed up my story and said that I was right," he said.

Aviation rules dictate that pilots communicate with air traffic control in English. It is unclear whether the conversation in the cockpit related directly to flight procedures.

Eagles said that, about a week after the incident happened, the airline sent a letter to all cabin crew and pilots that they “must speak English” from the moment they arrive at the briefing office until takeoff.

The airline did not dispute Eagles' account of the incidents in its reply to the . A spokesman said the company was sorry Eagles' employment "did not work out".

He went on: "HK Express accepted Mr Eagles' resignation and reached a signed mutual agreement to the satisfaction of both parties."

Owned by mainland firm HNA Group, HK Express is the only locally based low-cost airline.

But it is not the only local airline to face discontent from its pilots. In June, a source revealed that 35 pilots had resigned from sister company Hong Kong Airlines during the previous six months, a turnover rate unions called alarming.

Meanwhile, Cathay Pacific pilots voted last month to take industrial action in a dispute over their pay.

After Eagles' cockpit confrontation, he waited 2-1/2 weeks for another meeting with the manager.

During that meeting, the manager said the fault lay with Eagles.

Eagles told the manager he had felt like killing himself - a feeling, the pilot said, that was the result of depression at what had happened and a heavy drinking session with a friend.

The manager immediately stopped the meeting and took Eagles for drinks in a nearby bar. There, he said, the manager told him to see a doctor.

Eagles said he spoke to three doctors, none of whom said he was depressed, suicidal or had any mental health problems.

A doctor approved by the Civil Aviation Department certified that Eagles "had been assessed as medically fit to resume" flying.

Still, Eagles said, he was banned from work for 2-1/2 months until he was fired in July over what the manager said was his "very poor and bad behaviour, which was not expected of a Hong Kong Express pilot".

After an appeal, management agreed to change the sacking into a resignation to give both sides "a clean slate".

Now Eagles, who joined HK Express after working in Greece, fears he will be unable to find a new job as his licence has expired. Few airlines will hire a pilot without a valid licence.

Licences must be renewed every six months, and Eagles said the airline had finally agreed to let him take a renewal test after an argument - with only a day's notice. Eagles declined, as it usually took days to prepare for the test.