AdamFrisch

So I keep seeing these ads for AirNav's Radarbox. It's basically an antenna, a USB interface thingamagig and a little portable PC. It covers pretty much all the world.

So let's say I stuck this in my aircraft and hooked a PC up to it - would this show all radar traffic, or just the airline stuff? In their examples all you see is airlines, but I'm thinking it must return just normal mode c and s squawks as well, no? Does anybody have this system at home and can tell if that's the case?

Be a brilliant cheap TCAS system if it does.

HEATHROW DIRECTOR

All it shows on the "radar" display are aircraft transmitting ADS-B, i.e. their exact location. These may be any type of aircraft so fitted. All aircraft transmitting Mode S will be listed separately, but that would not be much use for what you suggest. There are some fancy internet programmes which claim to show the positions of aircraft not using ADS-B but I doubt that they would be accurate enough.

I'm not sure how it would function in a moving aeroplane, possibly not at all.

AdamFrisch

Thanks.

Then it won't be much use if it doesn't include all transponding returns.

Jan Olieslagers

I remember seeing a twin piston IFR trainer reported, but it is rare. And do not think I own such a device: websites like flightradar24 are based on the same information.

750XL

For the SBS-1 (Kinetics version of the 'Radar box') you need to set your exact home location, as far as I know they don't work very well when moving.

Radarbox/SBS-1 only show aircraft with full ADS-B, mostly newer Boeings/Airbus. CRJs, Dash8s, ERJs, biz jets, mil, GA etc don't show (normally) so it wouldn't be any use in the air.

BackPacker

Yep. I'm not the worlds expert on mode-S, but I seem to recall there's "Elementry mode S" and "Enhanced mode S".

Elementry mode S is what you will find in a typical spamcan. It's to a very large extent a mode A/C transponder (4-digit ident plus altitude encoding), plus the following:
- Transmission of a flight ID (e.g. your callsign)
- Transmission of the 24-bit (?) ICAO ID
- Selective responsiveness to interrogations: It only responds when the radar head wants to specifically interrogate your transponder, or when the radar head emits the 'all stations' signal.

Enhanced mode S is what you will find in the big iron. This transponder is integrated with the FMS and will include in its response various parameters of that FMS, including, but not limited to:
- Current pressure altitude and selected pressure altitude (stop climb/stop descent)
- Current heading and selected heading
- GPS/INS derived position

It's this last parameter, the GPS/INS derived position which is used by SBS-1 and similar "virtual radar" setups.

So as a TCAS-replacement it's not going to be much use unless your main worry is to be hit by "big iron".

And as far as ADS-B is concerned: I think (but am not entirely sure) that ADS-B is simply the encoding mechanism for the parameters that are both required under Elementry mode S and Enhanced mode S. So both types of mode-S transponder will emit an ADS-B signal, but Elementry mode S will only use that to encode a few parameters, and that list does not include the GPS/INS derived position.

bookworm

Actually, position is not one of the EHS parameters. They are:

Magnetic Heading
Indicated Airspeed
Mach No
Vertical Rate
Roll Angle
Track Angle Rate (or True Airspeed)
True Track Angle
Groundspeed
Selected Altitude
Barometric Pressure Setting

That's because the parameters are sent as a supplement to Secondary Surveillance Radar, which knows where the aircraft is by traditional radar location.

But what's nice is that the format of the EHS response is essentially interoperable with an ADS-B response which does include position.

No, not quite. ADS-B is the idea that the data is broadcast (that's the "-B") rather than waiting for an interrogation from ground radar. And of course if there's no ground radar involved, you need to add position to the broadcast. But the formats used are similar, so most EHS transponders can also do ADS-B. A bit more detail here.

FlyingStone

Worth mentioning that ADS-B uses GPS position reports (GPS itself must be certified, I think that panel installations of 296/496 wouldn't be allowed for ADS-B), not anything else based on self-sustaining navigation tools such as INS/IRS or radio-navigation based such as DME/DME or VOR/DME.

I think that given that the majority of VFR traffic is still not equipped with Mode S transponders (let alone ADS-B), the best thing you can currently buy is PCAS (Portable Collision Avoidance System) - it doesn't have graphical presentation, but I think the direction, altitude (relative or absolute) and vertical speed (well, indication of climb, cruise or level flight) is more than enough information to avoid any VFR traffic you don't have visual contact with.

I think the main problem with using ADS-B as a means of avoiding collision is that only large transport aircraft have it - and as it was mentioned, smaller regionals such as CRJ, ERJ don't, so you would be effectively protecting yourself only from A320, B737 or larger. Not quite the protection I'd want. I would also like to point out that the most dangerous operation (regarding posibility of mid-air collision) is VFR-VFR outside controlled airspace, since you have many non-transponding aircraft, which are flying low, many times below radar coverage (so FIS can't give you traffic information), many times there is a really poor lookout for other traffic, etc. What I'm not worried about is possibility of IFR-IFR or VFR-IFR collision in medium-busy controlled airspace, since most IFR traffic has MTOM over 5700kg and thus requires TCAS on board, and even if you don't know you are on a collision course, they will and they will avoid you.

I have to say that over-reliance on TCAS could be a problem, but is usually present with airline pilots. I've heard quite a few times at the airport I usually fly from that airliners are reporting TCAS TA/RAs to ATC regarding VFR traffic flying traffic patterns. All good and well if it wasn't the usual traffic pattern (obviously not as wide as an A320 would fly) and flight visibility was 50+ km. So all in all, I think the most important way to avoid collision is good lookout and when that's not available (IMC or otherwise poor flight visibility, such as flying directly into sun), one should begin relying on TCAS/PCAS.