ADS-B Aircraft v Positions


#1

Folks,

Viewing the rankings on my statistics page I noticed a user who has seen far more ADS-B positions than me but I have seen more ADS-B Aircraft.

What is the correlation between positions seen and aircraft seen?

Geffers


#2

if an aircraft flies directly overhead at say 45000 feet and you have good range you will get a lot of positions.

but if the aircraft just barely flies through your coverage due to altitude and range it may give you only a few positions.

so the other user might have better range than you but there are just less aircraft flying around his part of the world.


#3

But there also seems to be a variance depending on gain settings, and it’s not always higher gain, higher position and/or planes seen numbers.

Look at past gain settings threads.


#4

What is the correlation between positions seen and aircraft seen?
The longer you are able to track an airplane the more messages you will see from that aircraft.

Aircraft sent out about 1-2 transponder messages a second but only a small subset of message are useful to FlightAware. Less than 5% of the all the messages you receive locally are sent back to FlightAware.

The longer you are tracking an aircraft the more messages you will pick up. So assume about 1 message every ~20 seconds are being sent back to FlightAware.

You can get the average number of message per aircraft by dividing the two numbers.
So say you have 110,000 messages from 1700 aircraft. Average message per aircraft is 64 messages/aircraft.
So you get an average tracking time is in the order of ~20 minutes per aircraft (64 messages * 20 seconds between messages / 60 seconds in minute).

The problem is that aircraft on the ground send way more messages, planes changing altitude or direction messages are priority messages and sent back to FlightAware, aircraft flying lower are flying slower and will have a longer time being tracked, etc.


#5

Thank you for detailed explanation, that is interesting. I assume on Skyview then if the total messages are divided by two then that is roughly how many seconds of live viewing for that aircraft.

Appreciate nothing is exact but useful for us non pilots to understand a little of the statistics.

Geoff


#6

Which is further acerbated when the flight crew fails to place the transponder in standby when the aircraft has blocked in at the gate.