Concerns over Ryanair’s safety culture and support for an inquiry by regulators has emerged from a survey of the carrier’s pilots.

Europe’s largest budget airline by revenue declined to comment on the survey but said it had an “unblemished 29-year safety record”.

The survey was commissioned by the Ryanair Pilot Group, which is seeking to have the airline’s pilots represented by trade unions in negotiations on pay and working conditions.

Ryanair said it would not comment on the Ryanair Pilot Group or its survey, which is due to be outlined in a Channel 4 “Dispatches” programme tonight (Monday).

It also would not comment on whether any of its pilots were on zero-hours contracts.

More than 1,000 captains and first officers at Ryanair – more than one-third of the total number of pilots at the company – were contacted by the Ryanair Pilot Group.

The survey was prompted by a warning in April by Ray Conway, Ryanair’s chief pilot and a senior manager, that any pilot signing a petition – organised by the Ryanair Pilot Group and calling on regulators to evaluate whether the company’s employment model had an impact on the safety of flight operations – would be liable for dismissal.

Of those participating in the survey, 89% said that, following this memorandum from Conway, they did not consider that Ryanair had an open and transparent safety culture, the Financial Times reports.

Conway said in his memo that any pilot who had legitimate safety concerns should raise them through Ryanair’s confidential safety reporting channel or with the Irish Aviation Authority.

The survey found that 67% did not feel comfortable raising safety issues through Ryanair’s internal reporting system.

It also found 94% believed regulators should conduct an inquiry into the impact of Ryanair’s employment practices on safety.

Evert van Zwol, chairman of the Ryanair Pilot Group’s interim council, said it had a “strong suspicion” that the airline’s employment practices may be affecting flight safety, but had no proof, which explained why an inquiry was warranted by regulators, according to the FT.

He added a majority of Ryanair’s pilots were not employed directly but instead hired through agencies, and expressed concerns about their terms and conditions, saying many have so-called zero-hours contracts where there are no guaranteed working hours.

“The results of the survey are reason for very great concern and call for immediate action [by] all involved parties, to get working on a solution and lowering these [survey] percentages sharply down,” said van Zwol.

Ryanair’s 2013 annual report said safety is the company’s “primary priority”, starting with the hiring and training of its pilots, flight attendants and maintenance staff. Employees earn productivity-based incentive payments, including some for pilots based on their number of flying hours.

But the annual report said Ryanair pilots are subject to limits of 900 flying hours each financial year, as determined by Irish regulators. It added the average number of flying hours by pilots in 2013 was approximately 798 – a 5% decline compared to 2012.