FlightAware Discussions

What does FA records as "aircraft seen" ?


Following the outage of nov 11th, I have dug a bit into the numbers that FA reports for aircraft seen in the stats, and there are some things that do not add up or which I do not properly understand.

As stated in a previous post, I have noticed a steady downward trend of aircraft count in the daily stats from ~1800 down to 1200 over the last 10 days. I was under the impression that air traffic is more or less constant, so this seems quite a high variation. It this a normal variation over a month ?

As a consequence of the outage of Nov 11th, I have started PP to run and report flight in parallel with PiAware, while keeping my local virtual radar which only reports to my self. This morning when I look at the stats I see :

  • Pi Aware : 1410
  • PP : 1403 (actually started at 8AM, because Id changed, but reports seem to have caught up in the first 15’)
  • Virtual Radar : 1655

That’s about 20% difference between the local count and FA’s count. What am I missing? It seems that the downward trend started when I upgraded to V1.16

PS : I stopped PP this morning, because FA’s stats get doubled when PP and PIa report together.

Our stats are based on UTC currently, so perhaps you’re comparing different time windows?


My time zone is UTC+1 so ther shouldn’t be much difference because of this. There are very few planes tracked between 0 and 1 my time which make the last hour of the UTC day. And except for the first day of logging, this timeshift would be compensated by the previous day’s measures.

I have though about this issue a bit, and while you count aircrafts, VR counts flights. Their may be a difference there at 2 levels :

  • 1 aircraft on the reach of the reception zone can be counted twice if its signal is lost and the recoverd after a minute or more
  • Aircrafts doing shuttle service which many passage in a single day will be recorded as many time as they pass above my head in VR, when it is actuallt a single aircraft, and could as a consequence be recorded only once by FA.

I will run a couple queries to see if my second hypothese can lead to a 20% difference in the counts. Can you precise how you count aircrafts in the stats?

Edit : Ran queries on my basestation this morning and :

  • unique plane count is way below FA count so this is not the source of the discrepancy (1143 aircrafts for 2142 flights)
  • FA count for that day (11/03) was 1770

I agree with subsy about at least one question : what is the" aircraft seen" definition ? Is it a “select distinct” request from the database, giving the distinct planes seen during a day or a “select count” which would count several times the same plane entering the area then lost then seen again, etc… I have this feeling because of quite good stats from stations having obviously a very short range but showing a quite high planes count.

I am not involved in any race or podium but as a ham radio station, I have fine-tuned my receiving system and the result is quite deceiving compared to other short-range stations.

I have a question (which appears more or less in the PP forums).

If my station sees an aircraft then looses it for some time then acquires it again, does it count as 1 or 2 ?