Flight path deviation by AC856, CYYZ to LHR 15 May


AC 856 departed CYYZ at approximately 6:30 pm on a scheduled flight to LHR on Tuesday, 15 May. Almost three hours later, Flight Tracker noted that it suddenly reversed course and descended 4 000 feet before returning to its original flight track a few minutes later. This deviation still shsows in its log for that flight. As my daughter was on this flight, I was most concerned but was unable to find an explanation. As usual, Air Canada is almost impossible to reach by phone. The flight signal was not available on Tracker as it crossed the Atlantic and only reappeared when it reached the Welsh/English border and a successful arrival at LHR around the scheduled arrival time on Wednesday. Since my daughter is travelling, I have not spoken to her and don’t know if the passengers were aware of any problems.
Would this be an electronic signal error or is there some other possible explanation? How would I find an answer to this question?


Yea it looks like a bad position in there from one of the Canadian centers. We see this issue occasionally and do some work to detect the erroneous positions, but it doesn’t catch them all and we haven’t been able to get NavCanada to fix the underlying issue.