What was found
DURING CRUISE FLT AT FL390, THE LT & RT PNEUMATIC PRESSURE DROPPED TO 20 PSI. ENGINE DID NOT SURGE. STEADY VALUES, EPR 1.20, N1 90 PERCENT, N2 87 PERCENT. EICAS MAINT ECS MESSAGE SHOWED PACK OUT L28, R15. ALSO GAVE THE FWD CARGO HEAT AND EICAS BITE MESSAGES. TROUBLESHOT IAW FIM 36-10, FAULT TREE 862. PERFORM A BITE OF THE AIR SUPPLY MODULE. NO CURRENT OR PAST FAULTS. NO 30 DAY HISTORY. PERFORMED A TEST OF AIR SUPPLY SYSTEM IAW AMM 36-11-00-715-149. NO FAULTS. OK FOR SERVICE.