How does airliners appear on Hornet's sensors IRL?

[Darcaem]

Maybe this is more kind of a general question, but given the variety of each aircraft's sensors, and I mostly fly the hornet I though better asking it specifically here.

I've been wondering this for some time. In some of my missions I like to have some civil traffic, neutral airliners or GA. Thing is, if I set them as neutral, they are not shown as friendlies on radar or SA page (which is correct). If I set them as blue, they appear as friendlies and I can use SA page for example to see details about them. But I was wondering, how does this happen in real life?

Do they appear differently on the SA page in real life, as they would be using civilian squawk codes and transponder? Or the pilot would just be previously aware of civilian presence due to their flight plans being filed, or maybe some ground controller would notify?

[Pavlin_33]

There's no way any civilian airliner can respond as friendly. They all have same types of transponders.

[Muchocracker]

They show as unknown if there is no offboard correlation. 

Edited January 1 by Muchocracker

[Rongor]

3 hours ago, Darcaem said:

 If I set them as blue, they appear as friendlies and I can use SA page for example to see details about them.

Any IFF challenge wouldn't receive any response. Civilian aircraft don't have Mode 4 transponders.
If they appear as friendly via datalink, some AWACS or GCI might've designated these contacts as friendly, relying on other sources. If there is no such controlling instance, then any appearance as friendly is realistically impossible.

[Darcaem]

Ok, understood. Thank you all!