A 2017 contract seen by the Mail states that a steward would have a £175 'administration cost' taken from his salary if he left in the first 15 months.Of seven airlines contacted, Ryanair is the only one that hires through third-party agencies which offer no basic salary.
Agency cabin crew face costs of least £2,150 for training and £25 per month for uniform in the first year.
They are paid a £1,000 allowance in the first year, but this can be claimed back if they quit in this time.
Many crew said they estimated only about 20 per cent of colleagues were on direct contracts.
The Mail's reporter was told she could top up earnings through sales.
It said agency cabin crew's hourly wage for flight time covers all duty time, including on the ground, and full work hours are recorded as the law requires.