Insight - Is the public kept in the dark about Canadian air safety issues?

The tail of a Porter Airlines Bombardier Q400 turboprop aircraft is seen in Toronto, in this February 23, 2009 file photo. REUTERS/Mark Blinch/Files

TORONTO (Reuters) - Regulators threatened to ground Canada's Porter Airlines over safety problems in 2008, according to documents reviewed by Reuters, but the matter was kept secret for years - a sign, some critics say, of how little the public is told about the safety of Canadian airlines.

The documents, prepared by staff at the federal transport regulator, show that in early October that year, Canadian government inspectors scored Porter at only two on a scale of one to five, where five is best and three indicates compliance. The threat was first reported in the Canadian media in 2011 but the score and some of the reasons for it have not been previously disclosed.