The budget carrier on Sunday issued a public apology and admitted the fiasco was partly due to an exodus of safety trainers in June that had affected its number of qualified crew members and pilots.

“There is no way CAD staff involved in the process were not aware of this,” Ng said on a radio interview, adding that the department “was not doing a good enough job as a regulator”.

“If the crew want to extend licences by a month, the [CAD] would have had to sign off on it. Knowing this, wouldn’t it have been a sign that they didn’t have enough people, and that there was a risk of something happening?”

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Ng said the federation understood from HK Express employees that the severe shortage in staff and trainers had long been a problem and the airline was essentially “using five lids to cover 10 bins” to get by until the situation finally imploded last week.

HK Express chief executive Andrew Cowen said on Sunday the company had lost three key safety trainers and one training manager in August. The Post understands the trainers resigned after a dispute with senior managers. The resignations disrupted training for more than 700 cabin crew and pilots, who cannot fly until their safety licenses are renewed.

Examinations for licenses are conducted once every 12 months and cover aspects such as how to open plane doors, evacuations over water and land, and operating emergency first aid gear. The training could last up to two weeks.

Cheung Shu-wang, chairman of the Staff and Workers Union of Hong Kong Civil Airlines believed that a high-pressure environment and a mismatch in staff to trainer numbers may have been behind the departures.

“I heard some trainers would take a suitcase to conduct one training session, then suddenly be called away to help on another flight,” Cheung said on the same programme.

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He believed that as Hong Kong’s airport expanded and more destinations were served – especially by budget carriers – the department would have to think about how to improve the regulatory regime.

“The CAD cannot escape any responsibility here and should reflect and review its mechanism,” he said.

“Hong Kong is one of the top three busiest airports in the world and has a third runway in the works. If these things happen again, it will hit the airport’s reputation. We could lose out to other Pearl River Delta region airports.”

Assistant director general of civil aviation, Alan Shum York-lun, who oversees air services and safety management, said his department was following up with HK Express and would wait to see a report from the company in one week as demanded.

“They will need to explain to us how the problem developed, why they took so long to do this and why the decision was made so late,” Shum said.

But Shum conceded that there was no stipulated time frame on when an airline had to notify the department of changes to scheduling. He also argued that its manpower problems were “commercial decisions” out of the department’s purview.

“Our role is to ensure all their crew on-board have the necessary qualifications and training and whether each flight meets our standards. If you talk about manpower shortages, those are more to do with commercial decisions.”

Asked whether the department had known about the manpower shortage in trainers and approved an extension, Shum said he “did not have any information on that at the moment”.

Five complaints had been fielded to the council over the cancellations, mainly over failures to get through to someone through the customer service hotline. Wong urged all air travellers to study the fine print on their booking receipts carefully and to take out suitable travel insurance.