What does FA records as "aircraft seen" ?


#1

Hi,

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.


#2

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


#3

Hi,

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

#4

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.


#5

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 ?