What was found
FOLLOWING TAKEOFF, PILOT NOTED DECREASE IN OIL PRESSURE. PILOT ELECTED TO RETURN TO AIRPORT. UPON LANDING AND TAXI BACK TO RAMP, PILOT KEPT RPM AT APPROX 1,500 RPM TO KEEP OIL PRESS ABOVE READING (LOW END). DUE TO TAXIING AT HIGH RPM, BRAKES WERE OVERHEATED WITH THE RT BRAKE CATCHING FIRE BY THE TIME ACFT RETURNED TO RAMP. FIRE EXTINGUISHED. DAMAGE CONFINED TO BRAKE AND TIRE. INVEST REVEALED SEVERAL SMALL PIECES OF WHAT APPEARED TO BE DIRT OR SAND ON RELIEF VALVE SEAT ALLOWING OIL TO BYPASS THRUST THE RELIEF VALVE RESULTING IN LOWERED PRESSURE. (X)