Differences between data/flights and data/airplanes

[clash]

Hi,

I'm using Flightradar24 for time to time since some months, and today I discovered something I don't understand really well.
Let's say you would like to do a research by flight code: you obtain the last flights registered for a flight code, for exemple for UA3856, this.
You can also do a reserach by airline registration: you obtain the last flights registered for an airplane. Let's try N209WQ.

My problem is: Why the second result shows that N209WQ didn't fly in the last days, while the first result shows that, indeed, it flew twice on May 14th?
Same problem for N507LX.

In fact, in the whole Republic Airline's fleet operating for United Express (34x Q400), flightradar24 shows that 17 of them only flew during the last week, if you search by airplane's registration. But if you search by flight code, I guess the result would be different? What is the correct way to seach how many of these 34 Q400 are currently flying? (during last 7 days, for exemple) ?

BTW, nor Flightaware neither Planefinder have better results if you search by Airline's registration. For flightaware, the last N507LX flight was on april 19th, 2013!

Thank you for your help!
And please excuse my english.

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According to the "how it works" page, All Bombardier Dash models don't have an ADS-B transponder. Is that still accurate for recent Q400?

[Amper]

Q400 planes are mostly tracked by MLAT and they are MODE-S only planes. Not ADS-B with full info

[clash]

Thank you for your answer. I didn't realize that even brand new propjets still don't have an ADS-B transponder.
So if I understood it well, it means that inside Republic Airline's 34 Q400, around half of them are not currently flying in area where there is enough F-feeders to have a coverage by MLAT?

What I still don't understand is why data/airplanes says that N209WQ didn't fly recently, while data/flights shows it flew on May 14th? If the plane was not tracked my MLAT, where does this info come from?

And finally, why are FAA data not able to cover Q400 flights?

[YSWG]

Not all jets have ADS-B fitted, example is the Embraer E-jets.

[clash]

Not all jets have ADS-B fitted, example is the Embraer E-jets.

Thank you for that clarification.

About Q400 & the questions I'm asking above, does anyone know the reason for these differences of tracking?

[Oblivian]

Flight information is gathered from multiple sources cross-referenced. If some of the information cannot be referenced, it will not link it back to the same sources

ADSB-B = send callsign in the data and can be matched with established route and history
Mlat/Mode-S = not always a callsign = no accurate flight number matching

[clash]

Flight information is gathered from multiple sources cross-referenced. If some of the information cannot be referenced, it will not link it back to the same sources

ADSB-B = send callsign in the data and can be matched with established route and history
Mlat/Mode-S = not always a callsign = no accurate flight number matching

I see. So you mean that flight informations, like these ones, come from multiple sources, not necessary spotting? For exemple, the info saying that N209WQ will fly this evening from DEN to SLC?

But still: On may 14th, N209WQ was spotted by something (MLAT or FAA), because its route appears here, from start to finish!
However, that page keeps saying it didn't fly recently.
Could it not be a database problem?

[clash_]

Flight information is gathered from multiple sources cross-referenced. If some of the information cannot be referenced, it will not link it back to the same sources

ADSB-B = send callsign in the data and can be matched with established route and history
Mlat/Mode-S = not always a callsign = no accurate flight number matching

OK, I see. Then sometime Mlat/Mode-S send the callsign, and sometime not? Is that just random?
In the case below:

UA 3856, Denver - Salt Lake City on May 27th: We can see it's track from take off to landing (recorded by Mlat I guess?), and it's callsign: N196WQ (just below the map).
As this flight was not registrated in data/airplanes/n196wq, does that mean that the callsign was not send by the airplane, but came from another source? And that other source (which one?) is not reliable enough to register the flight in data/airplanes/n196wq ?
If I'm correct, it's something like "flightradar24 tracked a flight from Denver to Salt Lake City on May 27th, but we are not sure it was n196wq" ?

Then the following statement should be correct too: if I want to know which Q400 from Republic Airlines are currently in use, it's useless to check "data/airplanes" for all Republic's Q400, one by one. Is there another way?