What was found
DUCT PRESSURE SPLIT IN CLIMB BETWEEN 31 000 & 37 000 FT LEFT NEEDLE INDICATED 20 PSI, RIGHT NEEDLE INDICATED 42 PSI. IN LEVEL FLIGHT AT 37 000 FT RIGHT NEEDLE CONTINUED TO INDICATE 42 PSI & LEFT NEEDLE INDICATED 25 PSI. NEEDLES GRADUALLY CAME TOGETHER IN LEVEL FLIGHT AT ABOUT 30 PSI EACH. ALSO ALIGNED AT DESCENT AT 22 PSI. ACCOMPLISHED TASK 36 11 00 700 804 FOUND LEFT ENGINE HIGH STAGE VALVE NOT OPERATING SMOOTHLY. REPLACED NR 1 ENG HIGH STAGE VALVE PER M/M 36 11 06 OPS AND LEAK CHECKS GOOD REF M/M 36 11 00 700 801.