A GLIDER PLT AT 4700 FT OVER FDK REPORTS A NMAC WITH A TWIN JET THAT WAS ON ARR INTO IAD.

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ON SAT; JULY AROUND XA:00 I WAS TOWED ALOFT FROM FREDERICK MARYLAND MUNICIPAL ARPT BEHIND A TOW PLANE. I RELEASED AT 3000 FT. THE WEATHER WAS HAZY BUT I COULD SEE THE MOUNTAINS WHICH ARE 6 MILES FROM OUR TKOF POINT. WHILE FLYING AT THE 3000 FT LEVEL I SAW AN OCCASIONAL AIRLINER INBOUND TO DULLES THRU HOLES IN THE CLOUDS WHOSE BASES I ESTIMATE WERE AT THE 6000 FT LEVEL. AFTER SEARCHING FOR AWHILE; I FOUND A THERMAL WHICH ENABLED A STEADY CLB WHEN I CIRCLED FAIRLY TIGHTLY. I HAVE AN AUDIO VARIOMETER SO I DON'T NEED TO SPEND ANY TIME WATCHING INSTRUMENTS TO MAXIMIZE MY CLB SO I CAN KEEP A SCAN GOING FOR OTHER AIR TFC AND FOR BIRDS OR GLIDERS CLBING. AS I TURNED R THRU A SW HDG AT ABOUT 4700 FT AN AIRLINER CAME INTO VIEW ON THE R REAR EDGE OF MY CANOPY AND ALMOST INSTANTLY HAD CROSSED MY NOSE AND WAS GONE. I SAW NO LOGOS BUT ONLY THAT IT WAS A TWIN JET WITH ENGS ON THE REAR OF THE FUSELAGE. I HAD BEEN DOING TURNS THAT TOOK APPROX 20 SECONDS AND HAD NOT SEEN THE APCH OF THIS ACFT WHEN I WAS HDG N A FEW SECONDS BEFORE. WE ARE ACCUSTOMED TO FLYING IN FAIRLY HEAVY TFC OVER FREDERICK AND ALL OF US NOT ONLY KEEP OUR HEADS ON A SWIVEL; BUT ALSO WARN EACH OTHER ON THE RADIO ON 123.3 WHEN A POWERED ACFT IS APCHING. THERE WERE NO WARNINGS; HOWEVER ABOUT 5 OR 6 SECONDS LATER ANOTHER GLIDER PLT EXCLAIMED THAT A JETLINER HAD JUST PASSED UNDER HIM. I THINK CONTRIBUTING FACTORS TO THIS CLOSE ENCOUNTER WERE: 1. WHEN THE SUN WAS UNIMPEDED BY CLOUDS THE HAZE IN GENERALLY UP-SUN DIRECTIONS BECOMES LUMINOUS AND VERY HARD TO SEE SILVER ACFT (AIRLINERS) AND WHITE ACFT (GLIDERS). MY GUESS IS THAT I MISSED SEEING THE AIRLINER BECAUSE OUR COURSES WERE SO CLOSE TO COLLISION. WHILE I WAS HEADED IN HIS DIRECTION THERE WAS LITTLE IF ANY APPARENT MOVEMENT ACROSS MY CANOPY AND A SILVER NOSE; UNMOVING; BLENDS IN VERY WELL WITH THE HAZE. 2. IN VIEW OF THE FACT THAT THE INBND AIRLINERS ARE ROUTED OVER FREDERICK; A VERY BUSY GENERAL AVIATION ARPT WITH POWERED FIXED WING; ROTARY WING; GLIDERS; AND ULTRA LIGHTS ALL OPERATING THERE; THERE SHOULD BE A FIXED POLICY THAT AT LEAST ONE PLT SHOULD HAVE HIS HEAD OUTSIDE THE COCKPIT IN THAT AREA WHILE OTHER THE OTHER CAN DO THE APCH PLATE AND CHECKLISTS FOR THE MINUTE OR TWO THAT IT TAKES TO CROSS THAT AREA. IN HAZY WEATHER; A BRIEF WARNING PASSED ON BY DULLES APCH; THAT AIRLINERS ARE XING A BUSY GENERAL AVIATION ARPT WOULD ENHANCE SAFETY. WE SHOULD ALL HAVE OUR HEADS ON A SWIVEL ALL THE TIME. IN CLEAR WEATHER WE GLIDER PLTS CAN SEE THE HEAVIES COMING 20 MILES AWAY AND HAVE NO TROUBLE KEEPING OUR DISTANCE; BUT IN HAZY WEATHER WE CAN ONLY SPOT THEM MUCH CLOSER AND OFTEN DON'T KNOW EXACTLY THEIR PATH AND ALT UNTIL WE SEE THEM TOO CLOSE; AS WAS THE CASE SAT/JULY. 4. OUR GLIDING CLUB SHOULD PUBLISH A WARNING IN OUR NEWSLETTER AND ALSO WE NEED TO BRIEF OUR OPS DIRECTORS TO WARN PLTS DURING HAZY WEATHER TO KEEP BELOW 4500 FT IN THE FREDERICK AREA. CALLBACK CONVERSATION WITH THE RPTR REVEALED THE FOLLOWING INFO: THE RPTR REVEALED THAT THIS IS A VERY COMMON OCCURRENCE AND THAT IT IS JUST A MATTER OF TIME BEFORE THERE IS A MIDAIR COLLISION. RPTR INDICATES THAT PCT TRACON HAS ARRS LNDG RWY 19L/R INTO IAD AT 4000-5000 FT 30-40 MILES OUT WHICH PUT THE ACFT DIRECTLY OVER FDK. THIS IS THE SAME ALT AND LOCATION THAT THE GLIDERS FROM FDK ARE OPERATING. THE GLIDERS HAVE NO TRANSPONDERS AND THEREFORE THE ARR ACFT TCAS ARE UNABLE TO PICK UP THE GLIDERS. THE RPTR AND A LOT OF OTHER GLIDERS PLTS HAVE CALLED PCT TRACON NUMEROUS TIMES TO LET THEM KNOW OF THE PROB AND THAT THEY ARE OPERATING IN THE AREA. RPTR BELIEVES THAT PCT TRACON DOESN'T SEEM TO CARE AND GETS THE FEELING THAT THEY ARE SIMPLY BOTHERING THEM. THE RPTR OFFERED 3 SOLUTIONS. 1. THAT THERE BE A XPONDER DEVELOPED WITH A LOW CURRENT DRAIN SO THAT IT COULD BE PLACED INTO GLIDERS. 2. THAT THE CALIBRATION REQUIREMENT FOR XPONDERS BE RELAXED FOR GLIDERS DUE TO THE FACT THAT A GLIDER CAN'T JUST FLY TO A MAINT STATION TO HAVE THE XPONDER CALIBRATED. 3. PCT TRACON SHOULD ANNOUNCE THAT THERE ISGLIDER ACTIVITY IN THE AREA AND THEN VECTOR ACFT AROUND THE AREA. IT WOULD ALSO BE BEST TO KEEP THE ARRS AT A HIGHER ALT IN THIS AREA.