An investigation is under way after dozens of bag-scanning security staff at Birmingham Airport were found to have missed vital training.
At least two managers were sacked by contractor Mitie for "allowing untrained staff" to screen luggage before it was loaded onto aircraft.
The managers were accused of falsifying training records and failing to supervise exams, but one told the BBC he had been made a scapegoat.
Mitie said workers had been retrained.
The Civil Aviation Authority (CAA) is understood to be investigating the allegations, which relate to about 40 out of 120 Mitie staff members.
The ground security operatives, who screen hold luggage that is checked in by passengers, failed to attend refresher training they are required to do every 13 months.
The BBC has seen internal emails showing concerns were raised about training requirements by supervisors at Mitie as early as May 2022.
The CAA carried out an unplanned inspection of the airport in January 2023 and took files away.
Days later, Birmingham Airport instructed Mitie to deliver full re-training to agents, supervisors and duty managers.
Emails seen by the BBC show managers discussing the rapid training of 30 people at a time and fears of non-compliant agents impacting the airport's security operation.
In August last year, two of Mitie's duty managers were sacked for gross misconduct.
A letter accused the employees as being part of a "scheme" where "non-compliant and fraudulent" processes were "deemed as the norm".
One of the former managers, who had worked at the airport for 13 years, told the BBC he denied any wrongdoing.
"As a duty manager our job is to run the operation," the former employee, who did not want to be named, said.
"It's nothing to do with the training. All the training is done by senior management."
He claimed he had been made a scapegoat for problems that arose at Mitie during the pandemic.
Aviation expert Paul Charles, a former director of communications for Virgin Atlantic, agreed airports in the UK and their contractors had scrambled to plug staff gaps post-Covid.
But he said the Mitie training lapses were, in his opinion, a "high-profile breach".
"You only need one determined terrorist or person who is trying to carry out an attack of some kind to get one item through during the screening process for it to be a major incident," Mr Charles said.
Salil Bhargav Colge, an aviation lecturer at University College Birmingham, added the situation was serious for Mitie's reputation and raised questions over the airport's internal process.
Birmingham Airport said the safety of customers was its top priority and it informed the CAA immediately after issues became apparent through compliance monitoring.
A statement insisted all passengers were screened and searched by its own security, with Mitie responsible for screening check-in luggage only.
"At no point did our third-party security contractor screen and search customers," an airport spokesperson said.
Mitie, which has provided security services at the airport for more than a decade, said it had carried out an investigation and made all employees complete the full five-day training course again.
"We have strict professional standards, including ensuring that all our colleagues have the correct training and accreditation needed to carry out their role safely," it said in a statement.
"Any colleagues who do not uphold these standards have no place in our business."
A UK Civil Aviation Authority spokesperson said it could not comment on individual cases.