Commercial Fixed Wing
Flight Crew Air Transport Pilot (ATP)
Situational Awareness
ATC Issue All Types; Conflict Airborne Conflict; Deviation - Track / Heading All Types
Air Traffic Control Issued Advisory / Alert; Flight Crew Took Evasive Action
Procedure; Airspace Structure
Enroute to GRR we were notified by CLE Center and GRR Approach that there was glider activity ahead. We were about about 15 miles east of GRR at 5;000 FT below a 5;500 FT overcast when we spotted the first glider in a turn at our altitude approximately 3 miles ahead. We notified Approach Control of the traffic and it was quickly apparent that he did not hold this particular glider. The glider was white and could not be seen against the overcast unless it was in a turn. Approaching about 1 mile I turned 30 degrees left of course to remain clear of the traffic. Leveling the wings out of the turn we passed over a second glider and under a third clearing each by about 500 FT and 1/4 mile. Several additional gliders were visible on TCAS; but the 3 we avoided were not. Clear of the traffic I turned back on course and continued the vectors into GRR. We received advance warning from ATC that we were approaching glider activity and were assisted in avoiding the gliders that were using transponders but we were not aware that some gliders did not have transponders. The vectors we received did not clear us of the entire area where the gliders were active and allowed us to come way too close before visual contact.
Air Carrier Captain reports conflict with sailplanes 15 miles east of GRR at 5;000 FT. Some of the sailplanes were pointed out by ATC and detected on TCAS; but others were apparently not transponder equipped.