Audio alert chattiness

[T67M]

I tried the audio output from the PAW for the first time today, and while it definitely works and is useful, it is VERY chatty, especially for Mode C/S targets. Based on observations I made while flying an aircraft solo, it felt like an audio alert was issued every time any of the parameters changed - even by just 100'. Given that the alert is also very wordy, giving a precise altitude difference, the messages just never seemed to stop most of the time, to the point where I had to unplug the audio link in order to use the radio!

Whilst knowing the relative altitude is useful, I think this just needs to be "above", "below", or "level" (+/-100 feet), with maybe scope for "slightly above/below" within 300'. Giving the full "one thousand four hundred feet below" on every repeat could become distracting. It would be great if the alert for a given Mode C/S return was also inhibited for a while afterwards unless it gets significantly closer.

For ADS-B/PAW/FLARM returns, it would be great if the PAW could extend the projected track lines and only issue an alert if they will intersect within, say, an 0.5nm laterally/850' vertical bubble within 30 seconds (these figures plucked from the TCAS "TA" criteria for flights in the 2,350-5,000' altitude band), and include the predicted time-to-closest-approach in the audio alert. I was getting alerts today from airliners flying away from me and already 10km away, which even with the CAVU conditions were nearly impossible to spot. Spotting an aircraft at 5km is hard work, and at typical light aircraft speeds, they would still be 50 seconds away even for a head-on approach.

[Admin]

Thanks for the comprehensive report.

I am aware of the issues around ModeC audio alerts, this needs some thinking about, its difficult to associate the ModeC transmissions, because of course they do not have an ICAO code to distinguish them. So when an alert changes by 100ft as you say, there is no way of knowing they are the same aircraft, we will get there, needs some creative thinking. So for the time being I still class ModeC as BETA. As far as the visual alerts for ModeC is concerned, I am pretty happy with the behavior.

Regarding the the traffic reporting for coordinate aircraft, the alert zones probably need refining, or making user defined. I am not totally comfortable using a prediction engine for potential collisions, this puts a lot of responsibility on PilotAware which needs very careful consideration.

Keep the reports coming 

[T67M]

Thanks for the response, and I completely understand about the beta-ness of Mode C/S detection.

One thought on reducing the chattiness, could you pick up the Mode-A squawk code and use that to identify individual aircraft, matching the Mode-A and Mode-C altitude returns by approximate match in the signal level? Obviously this might go wrong with multi-use squawk codes (e.g. London FIS, listening squawks etc) but it would be a start.

Another thought is just to match the current alert with the previous one and inhibit it if there is only a small change, for example <500' altitude difference with the current alert messages, or the same altitude band (below/slightly below/level/slightly above/above) as I proposed above.

I understand your concern with the collision detection liability issues, but a user-selected set of parameters would be a great compromise. I'd probably go for something like 500'/4km personally - I want a reasonable chance of actually being able to see the aircraft, and a reasonable chance that the aircraft might cause me to adjust my flight path, but others might want more warning. I also want to avoid a constant barrage of information about every aircraft in the sky so that I miss the alert for the one that I REALLY need to know about!

One final thought - the most dangerous aircraft is arguably the fastest moving one - speaking from personal experience where I nearly had a head-on collision once, avoiding it with less than 10 metres of separation having spotted the aircraft ~3 seconds before impact. For "coordinate aircraft", would it be possible to have a different alert for a rapidly decreasing slant-distance (more then 50% of your own ground speed?) as a compromise between full collision prediction and simple traffic alerting. Maybe the message could be along the lines of "Incoming!!! 3 o'clock, slightly below."

Keep up the great work!

[exfirepro]

Hi Mike,

Very comprehensive feedback and lots of great ideas for potential development.

Without the benefit of the 'Hex Code' present in Mode 'S' transmissions, or the multi-million pound radar head that initiated the interrogation in the first place, it's extremely difficult to correlate squawks to altitude returns for Mode C. We already considered using received signal strength to correlate returns some time back in development, but due to the constant and irregular variation in signal strength, this is far from reliable as a 'common factor' (though I personally still think it is our 'best' option). Unfortunately in order to follow and compare returns, all signals need to be decoded then held and compared for at least three 'sweeps' of the radar head which requires considerable processing power and even then the potential for error taking into account multiple aircraft using the same squawk (7000, plus listening squawks and multiple allocation codes) was felt to be significant and could, we felt, easily lead to corruption of data and in effect the creation of 'false' target aircraft. For all these reasons, we decided to concentrate on identifying positive 'altitude' returns, (which is in itself difficult enough when you look into how these are transmitted) then use their signal strength to determine risk in the same way we currently do with Mode 'S'.

As Lee says, Mode-C is still 'Beta' under development, but he felt the need to release as users were clamouring for it. I need to discuss these issues further with Lee in conjunction with other development considerations and will give serious thought to how your suggestions might be incorporated.

In the meantime, can I ask what Mode C/S Detect Range setting you are currently using? One simple way (which you may have already tried) to reduce the level of alerts would be to try a shorter range setting . This will obviously decrease the range at which you receive warnings, though still usually to an acceptable level. In a similar manner, ensuring you are using 'realistic' vertical filters for Mode C/S will also help reduce unwanted alerts.

Regards

Peter
(Mode C/S Development)

[grahambaker]

I was going to post what follows a few days ago, but have held back to date firstly to see what others may be experiencing, and secondly to avoid appearing too negative about what I think is a great achievement (and getting better all the time!).

I went into Sleap last week, as short flight at 2000' altitude. I have the filters set quite tight, +/- 2000' and Mode S/C range set to short. There were two other aircraft in the vicinity - a club 152 doing circuits, and a Shawbury heli mooching about somewhere (I never saw it), both directionless and I assume Mode S as I was getting callsigns displayed.

As I approached, the alerts became continuous; as the heli manoeuvred, and the 152 went up and down, it was continuous stream of warnings changing to danger, back to warnings with separation heights being revised constantly. It was a complete and utter distraction, useless for alerting me if another target were to suddenly appear, and I pulled the wire.

I realise this is one of those almost irresolvable problems - you don't want people flying around with their heads in the cockpit, the occasional glance for navigation and traffic purposes should be enough unless alerted by a new target, or one potentially in conflict. To achieve that requires quite sophisticated logic, which just can't be supported with the data available on Mode C and S. Too many alerts and the whole system becomes either dangerous (head in cockpit all the time looking to see if a new danger has appeared) or a meaningless distraction.

TAS and TCAS work well for IFR in CAS as traffic is controlled, and unexpected alerts are therefore rare. Trying to produce something with a similar relevance in bandit country is quite a challenge. In the meantime, I'll be reducing my filter to 1000' and may well switch off audio warnings, depending on the parameters of my flight, until everyone carries either FLARM, ADS-B or PilotAware!

[AlanG]

Hi

I have not flown with the audio alerts from PAW but do remember being a little perturbed by a fairly constant flow when testing with Peter on the ground from close proximity to Edinburgh Airport.  This was during the beta testing for the Mode S alerts only prior to the Mode C being addedso can quite appreciate your concerns.
When flying I use the EasyVFR (my nav software of choice) voice alerts from my tablet and have been liaising with Rob Weijers (Lee's equivalent at PocketFMS) with the introduction of the traffic alerts from PAW to EVFR.  Rob's current thinking is to limit the traffic alerts to no more than one in a 30 second period.  I have suggested that this feels a little too long as a lot can happen in 30 seconds and am hoping to persuade him that this could:  (a) be reduced to 15 seconds or (b) is over-ridden by a "new" or "increasing danger" alert, otherwise I am much happier with the traffic alerts I get from this source.  The main reason for taking this route was to utilise a bluetooth arrangement to get the alerts into my intercom setup.  As with everything new there are other teething issues like constant 30 second alerts from an aircraft you are flying in company with but as these things come to light they are being considered and addressed both in PAW and at least two of the main Nav programmes.  Rob's fear is like yours, too many alerts become a distraction and I can concur with that.
For the relatively short length of time this system has been in the making and since full production the innovation and results are quite astounding and the willingness of others to work with it to add the functionality to their own products is testament to its achievements and excellence.

Regards
Alan

[T67M]

I agree completely that PAW is a significant step in the right direction, and please do not take any of my comments as critical - the core product is rock solid, and even the beta ModeC detection works incredibly well given how difficult it is, and the visual alerts are near perfect. My only comment relates to the chattiness of the voice alerts, especially for for ModeC targets. For reference, my PAW was set to 2000ft short range Mode C/S no filtering. I have just flown again set to 500ft ultra short range Mode S only, and there is a definite improvement, but it can still be a little too chatty for my liking.

I did try one other thing on the flight today - I half-unplugged the audio lead so that the alerts only came through in my right ear. This was a significant help in reducing the intrusion value during radio chatter. Could a "pan left/right" option be added to the configuration?

[exfirepro]

Hi again Mike/Graham,

Having flown to Sherburn and back in close proximity to Alan a couple of weeks ago, and been exposed to significant repeating audio alerts from high levels of traffic approaching and on the ground at Sherburn (it was the start of the LAA Fly UK) I fully appreciate your concerns about excessive audio warnings. Not easy, but I will discuss this again with Lee and see if there is a way we might safely reduce repeat warnings from bearingless targets without a detrimental knock-on effect on safety.

Regards

Peter

[JimN]

I had a significant problem with this on Friday eve.
Preparing to fly out of Sandy, no one there with PAW or Mode S/C and no obvious traffic in the sky in the vicinity, I had a 100% constant series of audio bearingless warnings about traffic at my level.
I found it impossible to think, and that was on the ground!
In the end I pulled the audio jack out.
I suspect it was traffic on the ground at Old Warden, 40' higher, but why it was so constant I have no idea.
On taking off I could see nothing and after heading north a couple of miles I plugged the jack back in and all was quiet with a couple of useful alerts later in the trip.

Although pulling the jack worked, some better form of quick mute or easily adjusted volume level would be a significant help.

[Admin]

I had a significant problem with this on Friday eve.
Preparing to fly out of Sandy, no one there with PAW or Mode S/C and no obvious traffic in the sky in the vicinity, I had a 100% constant series of audio bearingless warnings about traffic at my level.
I found it impossible to think, and that was on the ground!
In the end I pulled the audio jack out.
I suspect it was traffic on the ground at Old Warden, 40' higher, but why it was so constant I have no idea.
On taking off I could see nothing and after heading north a couple of miles I plugged the jack back in and all was quiet with a couple of useful alerts later in the trip.

Although pulling the jack worked, some better form of quick mute or easily adjusted volume level would be a significant help.

Hi Jim,
In order to understand what is happening, we need to know the following :-

1. What settings have you selected for the Mode C/S configuration ?
2. Does your aircraft have a transponder fitted, is it Mode A/C/S ?
3. Were the audio warnings accompanied with any visual warnings on your NAV tool (and what is the NAV tool) ?

Thx
Lee

[exfirepro]

Hi Jim,

Was just about to post when I noticed Lee had beaten me to it, so please read this along with his.

Can I ask what settings you had for Mode C/S vertical separation and Mode C/S range.

Also if you are transponder equipped, did you have 'Mode C/S Select' configured to Mode S (or Mode C/S) with filter to filter out your own transponder? This is unlikely to be the issue as you didn't experience the problems later on, but worth checking.

Looking at my charts, you are fairly near Luton, so might have been picking up what are effectively high power Mode 'S' ground radar responses from aircraft there, or aircraft holding in their pattern. From experience during testing, that is probably more likely than traffic at Old Warden. Your report that this disappeared as you headed north would also tend to support this.

Several options have been proposed to mute audio, but all have their disadvantages. We will clearly have to give this more thought, but as Lee says, let's look at your settings first.

Regards

Peter

[JimN]

Lee, Peter,

Settings:

Mode-S separation +/- 1000 ft
Mode-S detect Short Range

No Transponder

Warnings were for bearingless targets, I'm on Android SD and they still appear as a small plane over the big one. Didn't notice how many.
No aircraft on screen with a location & track (PAW/ADSB)

Wouldn't most (all?) Luton traffic have ADSB ?

Cheers

Jim

[Paul_Sengupta]

I don't know if FlyBe fly from Luton, but I've noticed they don't have ADS-B.

[Admin]

Wouldn't most (all?) Luton traffic have ADSB ?

Hi Jim,
Having an ADS-B Transponder does not disable Mode A/C transmissions.
If the transponder is interrogated for Mode A or C, it will still give a response.

I would still like to look at the tracks to get an understanding of what was happening.

Thx
Lee

[JimN]

Lee,

Exactly what is it you want to see, and how do I get it?

Jim