What was found
THERE IS NO INDICATION OF LEFT OR RIGHT FUEL BOOST PUMP FAILURE OR VALID CHECK PRIOR TO FLIGHT OR DURING MAINTENANCE. HAVE WITNESSED TWO FAILURES THAT ARE UNKNOWN TO PILOTS DURING FLIGHT OPERATIONS AND HEARD OF ANOTHER BY ANOTHER AIR AGENCY. THE ONLY INDICATION OF FAILURE IS REACTIVE IN NATURE BY UTILIZATION OF EMERGENCY FLIGHT CHECKLIST AFTER AND DURING ENGINE OPERATION ON GROUND OR IN FLIGHT THAT CAUSES A RAPID AND SUBSTANTIAL FUEL IMBALANCE TO WHICH THERE IS NO FUEL IMBALANCE INDICATION ON THE SAME AIRCRAFT.