Why does Estimated track not follow the lodged Flight Plan route

This flight on August 29 was showing an estimated route which did not follow the Flight Plan route that was shown on the page in the picture. The CC at the end of the fourth line of the Route list shows Cocos Keeling Island as a waypoint.

The Estimated track showed it travelling about 100km north east of CCK and then jumping to the correct position when Flightaware received actual location data.

Why does the Estimated track not follow the posted Route?


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I am not an ATC or a Pilot so take this with a grain of salt. So to start a flight the airline or the pilot file a flight plan that includes all those odd named way points in the sky with highways plotted between them. The ATC has a copy and they go over it to confirm the plan and any changes ATC wants to make. They have final authority. I think all commercial flights must file a plan. General aviation (smaller planes) may fly VFR (visual flight rules but have restriction as to height and airport permissions) so they don’t count other than they will be (mostly) required to use ADS-b by end of 2020 (that is an FYI). So flight Heavy123 is in the air and calls ATC and says man the turbulence is so bad that the salt shakers are losing salt can I move from FL 37 and I go to 39. ATC says yea but when the pilot gets to FL 39 it is just as bad. So he calls ATC again and says can I divert around this stuff and ATC says shure turn left to 160 degrees and you will be good. Now I don’t think ATC files a new flight plan. If that is the case then FA does not get an update but still shows the original track that was files on take off. After getting the plane past the weather he guides him back to his original destination.

And that is how a plane can deviate from a flight plan (of course emergency landings etc will all work as well)

Be aware that a commercial pilot cannot deviate from a flight plan to go check out the Grand Canyon or Niagara Falls. Everything short of an emergency goes through ATC. Sightseeing via ATC only.

I think the estimated track just doesn’t have full mapping information.

When i really want to see where the flight plan goes i paste it on skyvector.

(Also happen to have compared flight plans with estimated tracks around Sweet Peas station in the middle of nowhere. If you want to know if some of the planes will come by, plot the flight plan)

Or rather you can check for one of the routes that leads past the island, it’s about 2 tracks that have names that are normally in the flight plan.

Not quite correct.
The final authority is always with the pilot in command.
They work with ATC to ensure traffic and weather separation.

A commercial pilot can absolutely deviate from a flight plan. They do it all of the time. To maintain safety, ie airspace separation, they request deviation approval from ATC. If possible, ATC will allow it.

I knew the PIC is responsible for health and safety of the plane, passengers and crew/. But the point can’t just decide to sky hawking because he wants to (what is that called, a “deviation”?

Thanks for the backup on my scenario.

I too think Skyvector is great.

My question was simple. We know where the plane should be flying according to the flight plan.

For much of the flight over the great expanses where there is no data being fed to Flightaware they estimate the position.

Why does the Estimated Position not follow the flight plan?

I do but it is a rather long and tedious task to get the flight plan from the Flightaware site, copy and paste it to Skyvector to see if it should come into range of my site at CCK for every plane flying across the Indian Ocean.

Flightaware has the information but the plot something else. Why?


My understanding is that the airlines flying the longhaul routes into and out of Australia have access to modelling software that includes weather forecasts and they use that to plot the most economical tracks and waypoints.

Circumstances change en-route and the aircraft sometimes deviate for all sorts of reasons.

I usually fly further back in the plane where salt comes in little sachets so I can’t correlate turbulence causing spilt salt to flight path deviations.

My question was not about showing a deviation in the flight plan. I asked why Flightaware does not show the Estimated flight path according to the filed Flight Plan.

In cases where we have a reliable 4d flightplan we’ll use that for projecting estimated positions. Often, though, the flightplan isn’t considered reliable and/or it’s not 4d - it depends on the data provider.

Next time all take your questions with a grain of salt and your screen shot on a 48 in monitor.

Maybe I was in first class with a salt shaker. Maybe is was on a tanker refueling jets with a salt shaker. Maybe I was dreaming. Maybe it was meant to be funny.

LIghten up dude.

I am sorry but I don’t know what a 4d flightplan is. Could you please point me at an explanation.

In the example I gave in my original post the Flight plan is shown on the Flightaware page and includes a Waypoint at CCK. The aircraft in question did fly directly over the CCK waypoint.

How is that unreliable that you choose to show the estimated path to be considerably different?

A similar event happened yesterday as well so it seems it is an ongoing occurrence.



This is where the waypoints have a 3D position (latitude, longitude, altitude) and also the time - a fourth dimension - at which that position occurs. Sometimes we can infer a time-at-position from just 3D waypoints but it’s less reliable.

Unreliable in the sense of “sometimes the data for this is wildly wrong, so we can’t safely use it”. A common case of this is when an ANSP provides waypoint data for a route lying outside their service area, those waypoints can be badly wrong.

This particular case looks like the predicted path passed somewhat north of the real track (possibly because we didn’t understand CC as a waypoint), and we corrected it when we got real data and notice. If you look at the flight track after the fact you’ll see we’ve discarded the unreliable predicted position.

Just for interest, is this anything other than a position calculated from: a waypoint (2D) plus flightlevel (1D) plus filed altitude (1D)?

Flightlevel vs altitude are just different ways of expressing the same thing?

The interesting thing about a 4D position is that it tells you when the aircraft is expected at a given position.

Still one might argue that using a flight plan with flight info is better than just saying it will go direct destination.

In and out of JFK your flight plan data generally is pretty accurate yet the estimated track you display does not match that flight plan.

So i’m wondering how you arrive at the track with many corners instead of just drawing the flight plan?

Sorry, I wasn’t playing semantic games.
I was wondering if a 4D waypoint is simply calculated (predicted) as:
[x2, y2, z2, t2, v2] - [x1, y1, z1, t1, v1]
based on something like ‘time at wheels up’ or ’ last known (valid) position’
or is it predetermined when the flight plan is lodged?

I’d say the flight plan has incorporated a time interval for every leg according to predicted winds and planned speeds.

Now flightaware knows when a plane passes over a waypoint and it’s just linear extrapolation from there.

Or it has incorporated absolute times and flightaware just converts them to time intervals.