What was found
(CAN) APPROX 1/2 HR INTO FLT, FLT CREW NOTICED "IMPENDING FUEL BYPASS" WARNING LIGHT ILLUMINATED ON RT ENGINE. A/C RETURNED TO MAINT BASE. INSPECTION OF LOW PRESSURE FILTER REVEALED CONTAMINATION OF SMALL PARTICLES OF PRC & HARDENED SEALANT. THESE ORIGINATED FROM FUEL TANK ACCESS PANELS. INSP OF HIGH PRESSURE FILTER SHOWED NO SIGNS OF CONTAMINATION. A/C HAD RECENTLY UNDERGONE MAINT IN FUEL TANKS. FUEL TANKS WERE CLEANED PRIOR TO CLOSING OF THE TANK PANELS. FUEL FILTER ON LT ENGINE CHANGED AS PRECAUTIONARY MEASURE: CONTAMINATION OBSERVED ON LOW PRESSURE FILTER TO LESSER DEG. FILTERS WERE WELL WITHIN ALLOWABLE TIME IN SERVICE.