Hong Kong Airlines has been hit by an "alarming" tide of resignations with about 35 pilots quitting in the past six months, sources say.
Neither the budget airline nor the Civil Aviation Department - which said it had been kept informed about the resignations - would give details.
While the airline said the turnover was "normal", sources told the South China Morning Post that as many as 35 pilots had resigned since December.
David Newbery, a spokesman for the Hong Kong Airline Pilots Association, a body that represents three pilot groups in Hong Kong, said the resignation rate was "pretty alarming".
"[The rate] is certainly not normal and is unsustainable - particularly for an airline which wishes to grow," he said.
"Pilots are a long-lead-time item - they require training, which is time-consuming and expensive. You cannot replace a pilot as easily as you can replace a clerk or even a manager."
The resignations leave the airline with about 250 pilots to fly its 22 aircraft, sources said. Cathay Pacific has more than 2,900 pilots to fly about 140 aircraft.
The departures indicate an attrition rate of about 12 per cent a year compared to about 5 per cent for Cathay in the past few years, according to a pilot close to the Hong Kong Aircrew Officers Association. Cathay does not disclose its figures.
A spokesman for the Express and Airlines Pilots Association, which represents pilots at Hong Kong Airlines, said that there had been a recent "upturn" in resignations.
He attributed it to dissatisfaction with conditions of service, lack of a commuting roster and the beginning of a recovery in European aviation recently that had made more jobs available.
The exodus is the latest setback for the airline, which has rarely been far from the headlines since its launch in 2006. In November, transport minister Professor Anthony Cheung Bing-leung voiced concern about its safety standards after seven "deviations from regulations" on flights in August and September.
An internal document obtained by the Post in April showed that 28 pilots had resigned since December.
Sources claimed management had told pilots to fly more than the 12 to 14 hours stipulated by the department and not to report it or they would face punishment or risk losing their year-end bonus.
The airline denied forcing pilots to violate rules or encouraging them to falsify records.
"The most common reason for pilots leaving HKA is due to their desire to return to their home country," a spokesman said. "Other pilots leave to pursue broader career opportunities, both within the aviation industry and elsewhere."
The department said it had received complaints that some pilots had flown more than the permitted number of hours but had found no evidence to substantiate the complaints.