A former Air Canada pilot is accused of flying thousands of passengers on commercial flights without a proper licence for 17 years, officials say.

Police said the pilot, 59-year-old Geoffrey Wall from Ontario, was discovered to have been flying with forged credentials since he was promoted to captain in 2009. He now faces several fraud-related charges.

Air Canada said the pilot was immediately removed from duty once the false documents were discovered last year. "The company voluntarily reported the matter to Transport Canada," the airline said.

The airline said passenger safety was never at risk, noting that all pilots undergo competency training every six months.

Deputy Chief Nick Milinovich of Peel Regional Police said Wall had been flying with Air Canada for 27 years, beginning his career in 1998.

The pilot allegedly had been misrepresenting his credentials since 2009 when he was prompted to the position of pilot-in-command, or captain, police said.

For that role, pilots are required to have an airline transport pilot licence (ATPL), which is obtained partly by passing a series of written exams.

"This is very similar to a doctor that is licensed to practice family medicine, but is doing brain surgery in their office," said Milinovich.

For the last 17 years, police said Wall flew several types of Boeing aircraft and a total of 900 domestic and international flights, and earned millions of dollars in salary - all allegedly without the proper credentials.

Officials said the alleged fraud was discovered last year during a routine evaluation when inconsistencies were flagged with the accused pilot's licence documentation, prompting an investigation by Transport Canada, Canada's federal transport department.

Peel Regional Police, a force in the Toronto-area, then began a criminal investigation into Wall that included a search warrant and an analysis of the licence, which police said they determined was forged.

Wall was charged on 1 June with a total of seven counts, including fraud, forging documents and possession of counterfeit mark.

Air Canada said the pilot was fully trained with a valid commercial pilot licence, but did not have the ATPL required to operate as captain under Canadian regulations.

In its statement, the airline added it "takes this matter with utmost seriousness", and said that it completed an audit of its pilots and found no other issues with non-compliance.

Asked why Wall's alleged fraud went for years undetected, Milinovich noted that offenders can become "very good" at "deceit and trickery".

"It is not uncommon for fraud to continue for years and years," he said. "Eventually it catches up to you, and that's when we get involved."