If I understand correctly, with a ADS-B In equipment or TCAS equipment on board, the pilots could see the surrounding traffic with its assigned squawk code like "4653", is that right? But could the pilots know the aircraft identification like "UA858"?
ADS-B is part of a system that compromises a number of different things. ADS-B (In) means that your aircraft is capable of receiving the ADS-B data, FIS-B and TIS-B as well. FIS-B broadcasts information such as weather. TIS-B is a traffic broadcast system.
ADS-B includes a number of messages (about 27 different messages), including:
- Aircraft Identification
- Surface Position
- Airborne Position (Barometric)
- Airborne Velocity
- Airborne Position (GNSS)
- Aircraft Status
- Target State/Status
- Aircraft Operation Status
Each message packet holds 56-bits of data. The aircraft identification message includes the aircraft type, category, and callsign.
Now, to a pilot, here is basically what you would see:
You can see that some targets include the flight number (JBU1075) and clicking on a target (this is in Garmin Pilot) will give a little more information on the target:
What the pilots don't see is the squawk code, this information is not useful to pilots because they don't really care about that for other aircraft. The only real use of ADS-B target information is to understand where other aircraft are. If a pilot needed to call up another pilot, they would do so by tail number or flight number. ATC Controllers and other pilots will never call a pilot by squawk code.
Why? Because the squawk code changes potentially many times during a flight. Let's take for example a simple flight from KGRB to KMNM (a flight I'm familiar with):
On the ground at KGRB, when telling ATC about my destination they will assign me a squawk code, for example 2044. After departing they will call me up "1205C turn on course, altitude your discretion" and I will acknowledge. About 30 miles out (if I didn't get flight following) they will say "1205C squawk VFR, frequency change approved". Now my squawk code changes to 1200. I might then pick up Minneapolis Center if I want to change my destination and they will assign me a different squawk code.
The one thing that remains constant there is my tail number. I know to listen for (and have mentally trained a "listen up" trigger when I hear) "1205-charlie" or "05-charlie" on the radio. ATC has been talking to specific aircraft using the tail number/flight number since the ATC system was born. Squawk codes match aircraft with targets on the radar (because before ADS-B all that was transmitted was the squawk code). This information is only useful to ATC and not other pilots.
Now if I'm cruising around and I see a target on my ADS-B that is headed in the same general direction I am, and I'm not talking to ATC, I can try calling that target using the tail number/flight number directly (this is done on the air-to-air band or a local frequency, don't broadcast on 121.5 or you'll hear "guaaaaarrrrrrd" from some obnoxious pilot).
Either way ADS-B is useful for traffic avoidance. I don't really need to know where that airplane is going, why it's going there, etc. I just need to know what it is (big jets can cause wake turbulence issues for smaller aircraft), which way it's heading, and how fast it's going there.
The display depends on the equipment used. For example, the Avidyne 540 Pilot Guide says this:
For Mode-S equipped aircraft, the aircraft ID (e.g. tail number, call sign, etc) may also be displayed adjacent to the traffic symbol.
Normally I see a solid white diamond with a dotted line leading away to indicate direction, + or - how many hundreds of feet above or below me that traffic is, and an arrow if the traffic is climbing or descending. That would be plain ADS-B Out from other small planes like mine.
The diamond may also be hollow, blue, a yellow circle, a white arrow, a yellow arrow, all meaning different things. I'm not going to copy all descriptions from the Avidyne manual. One can read more here https://www.avidyne.com/support/doctype.asp?doctype=pilot%27s+guides&list=doc Scroll down to IFD-xxx, download it, and then page 3-39 for Traffic Display in the April 2019 release.
If the traffic is close enough, I'll also get a "traffic, 1000 high, 2 miles" kind of aural message over the intercom. Typically when other traffic are nearby in the pattern, or perhaps when crossing paths at intersecting angles (like me at VFR and IFR traffic going by 500 feet above or below).