What was found
AIRCRAFT RETURNED TO PLATFORM AS A CONSEQUENCE OF DURING ENGINES START, APU SHUT DOWN, FAULT LIGHT TURNED ON AND EICAS MESSAGE APU FAULT WAS DISPLAYED. THE FIM 49-11-00 PROCEDURES WAS PERFORMED. THE ENGINES START WAS PERFORMED WITH GROUND EQUIPMENT, ALL CORRECT. DURING OVERNIGHT CHECK SURGE VALVE AND GEARBOX VALVE WERE REPLACED IAW MM 49-53-01 AND MM 49-27-11, RESPECTIVELY. TESTS WERE PERFORMED AND BOTH ENGINE WERE MOTORIZED AT 30 PERCENT OF N2 IAW MM 49-00-00, OPERATING CORRECTLY THE APU.