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When you know there is traffic very close but you cannot see it...

So I was flying through German skies recently with a basic, (i.e. no glas panel or any way to show traffic on a display) PA28, it was a hot, sunny day.

Cruising along at 6,500 feet, scattered clouds about 1,000 feet above me. I see a glider to my left, he is almost as fast as I am, going some direction. Keeping an eye on him and think: gliders are like best friends, they never come alone. And indeed, I spot a second one at my 1 o’clock. This one circles up the thermals, no factor. My FLARM system dutifully reports the first one with 0.8 NM distance on my 4 o’clock position same altitude. Second glider never got picked up and I estimate I never was closer than 1 NM.

Suddenly, the FLARM goes crazy: 0.5 NM, 0.3, 0.2. Unspecified direction and altitude. I look out like an eagle and all I can see is: nothing. Think I’m gonna die. After about 10 seconds the alarm is over and I still don’t know what happened. I just kept my heading, altitude and speed all along. I think it might have been a glider shooting down from a higher altitude and try to “race me” or even just a false alarm by FLARM, have observed a few of those, too.

- What is the standard procedure here? Do some kind of “evasive maneuver” (which direction/altitude, how abruptly)? Rock Wings? Do nothing?
- One thing I have concluded for myself is that next time, I will try to steer away a few NMs as soon as I spot the first glider. Likely there is some kind of thermal and they are clustered together.

Somehow this is the part of flying that I struggle the most with, I have trouble spotting traffic (would say I miss about 30% of the traffic that I know about from either FLARM or ATC). And I fear that sooner or later there will just be a mid air collision.

Switzerland

For gliders flying patterns,
To avoid gliders (in G airspace), fly above cloud base if you can, if not avoid flying bellow large fluffy cumulus, bellow half cloud-base they tend to climb thermals at low airspeed ~40kts, above half cloud-base they fly fast ~120kts to the next thermals, few of them go bellow 2000 agl far from base (natural selection and time to land in a field)

As you mentioned, if you see one there are others, keep in mind that they usually keep good lookout: good canopies with wide visibility and unlike powered they have nothing interesting to watch inside the cockpit, so they have more chance to see you first

For FLARM,
I think you just need to know there is a traffic around, it is not very reliable for height and collision avoidance, with gliders FLARM just goes crazy when they thermal, so the same as using for the circuit you know someone is there and you trust your lookout (I switch it once I am inside the ATZ as it alerts me for aircraft parked on the ground )

Unless you see a collision or directed by ATC/TCAS, I don’t see why you have to start any standard avoidance procedure? personally, I will keep speed and heading and I will not rely on “FLARM signals to avoid traffic”, I think many view it this way?

Last Edited by Ibra at 29 Jul 18:42
ESSEX, United Kingdom

Do you have a classic Flarm or a PowerFlarm? Because Flarm to Flarm you should have directions and height difference.

Nympsfield, United Kingdom

OK so I guess I am too paranoid then. It’s just this kind of scenario playing in my head, especially when the distance decreases more and more and I don’t see anything :)


Ibra wrote:

Unless you see a collision or directed by ATC/TCAS, I don’t see why you have to start any standard avoidance procedure? personally, I will keep speed and heading and I will not rely on “FLARM signals to avoid traffic”, I think many view it this way?

Hmm the more I think about the more I feel at least rocking wings should be a benefit in safety? I am not changing course or doing anything abruptly, but at least my visibility should increase because of it?

Edit: cannot get youtube link to work, anyway, the video is called “Fatal Midair Collision At Idaho Backcountry Fly-In”, start at sec 47

[youtube link fixed]

Last Edited by HBadger at 29 Jul 19:23
Switzerland

If you know there is other traffic and you do not know where it is, one thing you can do is make yourself visible to others by banking and turning. This increases the surface of the plane which is exposed to other observers and increase their chances to spot you.

LFPT, LFPN

Why are transponders not mandatory for gliders?
Flarm usage is proof that they feel a need to separate from each other so why not from other traffic? Crazy…

EASA CB IR Training
Europe/Austria

Yes, rocking wings to check what is bellow and get visible, a smooth descent on cruise or faster speeds with forward visibility may also help

My view is that you will not hit something ahead of you unless you see it first, the scenario of hitting someone ahead of me or descending on someones back is highly unlikely, so worth a try (I did flew gliders in gagles with more than 15 in one 3000ft thermal, as I start losing track of half of them I just fly away in a straight line with stick slightly forward, full of shame but alive)

On airplanes, I only care about what is in the +/-60 degress ahead, tough, I have been overtaken by a twin with twice my speed that scared the hell out of me one day (I hope he saw me, so now I not tempted by chandelles when the flarm sings: “1nm and closing”), the best you can do is to ask deconfliction, avoid busy routes and hot spots, fly semi/quadrant hights with weired rounding xx66.6ft hehe (personally, I don’t beleive that much in the effectivness of lookout on a long cross-country flights, but I get reassured by statistics of random traffic collisons, the perephical ones I tend to spot them in go-pro replays and not when flying)

ESSEX, United Kingdom

Snoopy wrote:

Why are transponders not mandatory for gliders?
Flarm usage is proof that they feel a need to separate from each other so why not from other traffic? Crazy…

But how many GA aircraft are equiped with TAS or even PCAS? or are you relying on radar equiped FIS?
Glider on glider mid-air collisions are much more likely than with other aircraft. That why Flarm is popular.

Nympsfield, United Kingdom

Snoopy wrote:

Why are transponders not mandatory for gliders?

Transponders are not primarily intended for collision avoidance systems but to be picked up by ground stations. That means they emit signals with a fair amount of power. High power consumption means that lots of batteries have to be carried. FLARM is intended only for collision avoidance (and is uncertified thus doe s not need to be as reliable as a certified system) so it works with much lower power levels.

ESKC (Uppsala/Sundbro), Sweden

Most of the ones that go long cross-country have transponders and even engines, the ones that stays locally don’t even have a battery/radio. Those in middle range, have flarms but I never thinked of it as separation tool (deconfliction service) but rather to indicates GA traffic around (traffic service) or the next glider coming to hit you from the back

Even transponders (mode S or even XYZ) are worthless for collision avoidance and separation, you need ATC/TCAS and few traffic load to get meaningful separation signals…

Again as we are talking class G airspace, see and avoid or having another guy to help with lookout is what saves the day but flarm as a tool really helps to keep the alerte going (you are not alone) but it should not disturb your primary pic role, sometimes it gets you lost in a simlar fashion as when atc tells you about non identified traffic close to you

Last Edited by Ibra at 29 Jul 20:31
ESSEX, United Kingdom
25 Posts
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