The Globe and Mail reports in its Friday edition that U.S. President Donald Trump on Thursday declared on social media he is "decertifying" all Canadian-made aircraft and threatening to levy a 50-per-cent tariff on any Canadian planes sold in the U.S. The Globe's Eric Atkins quotes Mr. Trump saying the Canadian government has "illegally, and steadfastly refused to certify" General Dynamics' Gulfstream jets. "We are hereby decertifying their Bombardier Global Expresses, and all aircraft made in Canada, until such time as Gulfstream, a great American company, is fully certified, as it should have been many years ago," he wrote. "If, for any reason, this situation is not immediately corrected, I am going to charge Canada a 50 per cent tariff on any and all aircraft sold into the United States of America," Mr. Trump wrote. John Gradek, who teaches aviation leadership at McGill University, called Mr. Trump's description of the matter nonsense. Gulfstream has changed the electronics and navigation system of some of its models to extend their flying range and payload, and the Canadian aviation regulator is reviewing the changes, he said. "We haven't decertified the Gulfstream; we are looking at the paperwork," Mr. Gradek said.