On Saturday, October 14, 2017 at 6:03:20 AM UTC-7, wrote:
After passing by I checked my PowerFlarm and found no transponder target..

For powerflarm to see a Mode C or Mode S transponders, the target needs to be interrogated by a ground station or another aircraft.
The powerflarm itself does not interrogate does it?

As Jon said yes that is correct, and when a fighter is close to the ground its possibly not interrogated by ground based SSR radar. It might be interrogated by airborne TCAS/TCAD systems but even then you may have line of sight obscuration even if there are airborne interrogators around and within range (at least several tens of miles) . And then the glider would need line of site to the fighter jet to receive the PCAS, and you have limited PCAS range and time to react.

PCAS receivers including PowerFLARM might not be much help against fast moving targets in these situations even if they are being interrogated. 1890ES In on the PowerFLARM, if the fighter was equipped with 1090ES Out (and using it) would be more help, but even then down lower the glider pilot may not have many options and not able to guess what the jet is going to do. Getting them to see you via transponder is probably better first layer of technology assistance.

If you fly near fast military traffic I would encourage folks to contact the appropriate ATC controllers (civil and/or military) or air base. The military side especially will likely have a MACA (mid-air collision avoidance) program and somebody there will *want* to talk to you, take it as a time for both sides to educate each other on what what is happening. what equipment ((transponders, ADS-B, PCAS, IFF, etc.) the aircraft have. Many USAF air bases will have MACA information on their web site and who to contact. Fast fighter jets may have active IFF interrogators capable of seeing your transponder (ask them specifically about that). Civil and Military controllers watching over an MOA may also be able to see your transponder on SSR. Military transports and larger aircraft often have full TCAS II. All only useful if your glider has a transponder.