Recently, I was on a flight from Montreal to Vancouver. We were somewhere between Calgary and Vancouver when we started to fly strange manoeuvres:
The whole flight can be seen on FlightAware. We were definitively not yet approaching Vancouver airport and from the entertainement system I could see that we were at around 40000 feets, flying almost full speed.
So what are potential reasons for this flight pattern?
I called a friend who is a jet airliner pilot and showed him this question, he said there are two possible reasons for this:
There was some traffic or some sort of closure to the airspace, and was asked by the ATC to take a 360 until things are cleared.
He was asked to lower the altitude immediately, and to do that without going further into the route in the wrong altitude the captain did the 360 to have some space to lower the altitude before continuing the original route.
Both are normal actions.
Loops like that are usually about timing: it's an easy way to delay the airplane's arrival by a few minutes. By doing it in the middle of nowhere rather than the crowded airspace around the airport, it keeps things simple for air-traffic control.
FlightRadar24 shows the loop as well, but not the zig-zag, so I'm guessing the latter is an artifact of FlightAware's tracking system.
The loop itself is a way to delay the flight - to make it fit into the landing schedule at destinatioin, probably.
But what about the north-south zig-zag after the loop?
Somehow, it looks like drawing one invalid measurement that was shifted north by some error. But looking closely, the part is not just one point - the end of the zig-zag is curved, for example.
Computer scientitsts intuition tells me that it is an artifact of an algorithm trying to fix an outlier point.
What goes wrong is that the algorithm tries to estimate "how it should look like" based on a part before, of some length. But it does not expect loops in the part before - so the correction gets confused. The result of the correction is then affecting more than one point.
After the plane exited the circular holding pattern, the jump in position is probably just an erroneous transponder report (could be data corruption, inertial reckoning vs. GPS source, etc) and the plotting software decided to fit it on the line instead of rejecting it. This is relatively common - for a particularly extreme example, look at this:
N73259 was actually flying in a relatively straight line - 737s don't make sharp turns every couple miles.
It is a funny move indeed.
When you zoom on the place it happens and display the layer "IFR High En Route" on the map of FlightAware, you can see the airport of Penticton. On its website, we can see that their fees list suggests that large planes can land there. Indeed, its runway is 6000 ft long and the Airbus A330 (operated on that flight) can land on approximately 6000ft long runway. So it looks like this airport is ideally located for emergency landing of planes flying on a transcanadian routes.
This is just a hypothesis, but maybe the pilot noticed something weird at that point and preferred to fly over the airport again in case. It might also be that another plane landing or leaving Penticton airport would disturb your plane by forcing it to follow some corridor, even though the planes arriving or leaving on March 8 seemed on time and not happening between 7 and 8PM PDT, which may be the approximate time it happened.
