Displayed Track <> GPS Track


#1

Note the holding pattern in:
flightaware.com/live/flight/N992 … 0Z/I69/I69

It appears as if N992WW is entering the hold on the north side of the fix but my GPS track confirmed that we entered as published (204.108.4.16/d-tpp/0805/00083IL21L.PDF) on the southwest corner, turned northeast and then turned right and back to the west for a normal entry to CALIF. Again, the actual track was reasonably close to the published track.

I’ve seen several discrepancies between actual tracks and those presented … can you explain?


#2

I can partially answer your question and suggest something.

Regarding discrepancies, the quality of your GPS signal may affect how accurate the track may be. On my 296, it shows the actual accuracy of the GPS down to the feet on the page that displays the bars for GPS satellites. This may differ then what your transponder transmits to center or approach because the two units may have a different signal strength. Theory anyway for what it’s worth.

Second, regarding the hold entry, check out flightaware.com/live/flight/N992 … 9/tracklog and note the GPS coordinates. You may want to plot the coordinates as that will show you direction of flight.

For my Garmin 296, I have a program called Mapsource where I can download the data from my GPS.

Map derived from Mapsource on a hold I had to do on an Angel flight is displayed below

Hold wasn’t captured on Flight Aware as I was handed off to Little Rock Approach and they marked me as arrived.

flightaware.com/live/flight/NGF4 … /KMBO/KSRC

So I was glad I had the handheld GPS going so I could evaluate the quality of my hold.

Never made it to Searcy as you can see, ended up diverting to Melbourne AR.

100 foot ceilings and 0.25 vis at Searcy and and 0.13 at Little Rock sent all sorts of planes spinning in circles.

Hope this helps.

Allen


#3

What Allen said.
You are right, FA makes it look like you entered the pattern directly into the outbound leg.
The radar returns are not all that accurate, enroute radar updates approximately once every 12 seconds, in between returns a straight line is drawn which may or may not show every little turn that you made.
I see that the Cincinnati tracon was handling your flight so the drawing should be more accurate. This is a great example of why approach controllers keep aircraft at the same altitude at least 3 miles apart. With ADS-B and the other stuff coming down the pipeline we should see procedures being drawn up that allow aircraft to pass each other with less than three miles separation.
I think the main reason we are all confused is that you were holding at CALIF while flying over OHIO.
:laughing:


#4

Curious to know what you’re hearing about widespread availability of ADS-B.


#5

J. Mac wrote about it in the Feb 2008 Fying. Online version of that article is here: flyingmag.com/article.asp?se … cle_id=890
I would post an exerpt, but the infamous DEBUG Mode thingy comes on when I tried it.


#6

You need to make sure the excerpt has only keyboard characters in it. Anything like foreign accent symbols or bullets will cause the debug mode to happen.


#7

I haven’t heard anything recently about widespread use of ADS-B. I’m afraid it will become a typical FAA 20 year plan.


#8

J. Mac said sometime after 2020. However, the entire UPS fleet has it installed. It helps the pilots to self-space themselves with all the other UPS guys landing Louisville at the same time.


#9

Probably due to the temporal granularity (1 minute or more) of the radar positions we receive and the short duration of the entry.