Mooney_Driver wrote:
Almost certainly a glitch FR24 is notoriously unreliable when it comes to these things, therefore it really is only “entertainment”, otherwise it will give you a heart attack at times as planes vanish without a trace
I did almost get a heart attack the other day. The Swedish Rescue Coordination Centre called me (as club chairman) about an overdue aircraft inbound to our airfield (flight plan not closed). I checked FR24 and the flight track ended suddenly at 1500 feet several miles from the airfield… It eventually turned out that everything was all right and that there had been a mixup of flight plans.
I’m still somewhat puzzled why my “Proxalert” traffic monitor didn’t show them. It has an external antenna, and I regularly see (both on the monitor and by my eyes) traffic on it.
The plane came from the Isère valley in the South, which is wide open that point. So there shouldn’t have been any signal obstructions due to terrain in the few minutes before and after the encounter.
Of course the traffic monitor shouldn’t be taken as 100% reliable but merely an aid, and nothing replaces a good lookout and radio calls, but an uneasy feeling remains about why the device didn’t trigger.
If they fly through valleys in the Alps to and from Courchevel, you are most likely hidden by the mountains from radar as well as ATC, except for the A/A mountain frequency.
Zorg wrote:
Could this be a glitch of FR24, or is it realistic that such a plane would fly some legs with transponder off (for privacy or other reasons)?
Almost certainly a glitch FR24 is notoriously unreliable when it comes to these things, therefore it really is only “entertainment”, otherwise it will give you a heart attack at times as planes vanish without a trace (even ADS-B ones) and sometimes reappear, sometimes not. I’ve avoided telling people who are to meet me or my family to track my flight via FR for that reason.
If they fly with transponder off, it’s illegal and I doubt a PC12 crew would willingly do that.
AeroPlus wrote:
I am not sure how you can avoid it other than to fly on the right-hand side of the valleys and not in the middle and to keep a sharp lookout.
Proper radio procedures, at least in the vicinity of airports, helps a lot IMO. Also, use common sense. Don’t do evasive maneuvers if you don’t know where the other aircraft is. That will usually create more confusion for others that already have you in sight, or have an idea of where you are. To continue on the course or pattern is usually the best choice, unless you positively need to change it to prevent an accident.
About 15 years ago I went to Southern France in early spring to enjoy the early season start as a glider pilot. It was fantastic, gorgeous weather, breathtaking views, I had a great time. The only thing that was always in the back of my head was the fear of a mid-air collision since I had known at this time quite a few acquaintances who had been unlucky enough to be involved in a mid-air. Of course I had FLARM, and I was as vigilant as I could. Then, one day flying the ridge I noticed the FLARM beeping like mad and despite looking out I could not see that traffic. Until I noticed the other glider passing BETWEEN me and the ridge at more or less the same level.
I continued home, put my glider into the trailer, and have never come back there since. That´s my way to avoid mid-airs down there. I just don´t want to take the chance anymore.
I believe the overall risk in the mountains is higher than in the flatlands because traffic concentrates a lot more along certain routes. However, I think in summer the risk is considerably smaller because of the higher vertical range of usable airspace, also there´s less snow disguising other traffic.
I am not sure how you can avoid it other than to fly on the right-hand side of the valleys and not in the middle and to keep a sharp lookout.
Peter wrote:
Zell am See
It is really bad there especially on weekends and holidays with good weather. High performance planes mixing with motorgliders and pilots of various experience levels. It’s especially bad when para jumping brings a halt to the flow and planes are concentrated at areas while holding. LOWZ should be RMZ (radio mandatory) and TMZ (transponder mandatory). There has been loss of life there due to collisions.
I’ve had this sort of thing departing from Zell am See, with somebody right below me, climbing +1000fpm like I was, and me doing a tight turn to avoid the mountain (when doing the silly left turn over the lake). Luckily separation was somehow maintained…. never saw him. Next time I won’t fly to the west but will fly up the northern canyon (towards Salzburg) and climbing continuously.
Your Mode C/S was the best idea by far. The PC12 would have seen you.
WillC wrote:
Another thing to remember is that there can be quite a difference in QNH in a small area. I recall that being told to me during training and therefore when the tower at Courchevel is not manned there is a way of setting the QNH with respect to the top of a lift. I do remember that the Geneva QNH and the Courchevel QNH that I was once given were significantly different.
Good point … I can only hope that the PC-12 had my mode-S transponder on their TCAS since a while and decided to buzz me a bit 
