What was found
JUST PRIOR TO APPLYING TAKE OFF THRUST (JUST ABOVE IDLE THRUST) AND THE ANTI- ICE, ON WE RECEIVED A R HP VALVE CLOSED CAS MESSAGE. I APPLIED A HIGHER THRUST FOR TAXI AND THEN BROUGHT THE THROTTLES TO IDLE WHICH IS WHEN THE CAS MESSAGES CLEARED. CORRECTIVE ACTION: RESOLUTION: MCC HAS PROVIDED HISTORY, THE LH HP VALVE WAS REPLACED AND THE LH/RH DP SWITCHES WERE SWAPPED ON 12/16/25. SPOKE WITH THE CREW ABOUT THE DISCREPANCIES AND POSSIBLE VARIABLES THAT PLAYED. TECHS GAINED ACCESS TO AIRCRAFT AND POWERED UP IAW AFM. PERFORMED ARES DOWNLOAD AND SENT OFF FOR REVIEW. TECHS STARTED BOTH THE LH AND RH ENGINES AND PERFORMED WING/STAB A/L CHECK IAW CES80A MM 30-10-00 AND 30-15-00 AND FOUND NO DEFECTS. IN ADDITION, PERFORMED THE NIA AOM ANTI-ICE CHECK AND WERE ABLE TO DUPLICATE THE PILOT WRITE UP. PERFORMED THIS TEST 3 ADDITIONAL TIMES AND NOTED THAT B/A SUPPLY TEMPS, WING TEMPS, STAB TEMPS, AND ENGINE TEMPS ALL MATCHED LH TO RH. WITH THE ENGINES AT IDLE, THE APU B/A OFF, AND A/I SELECTED THE HP VALVE CLOSED L-R CAS WOULD POPULATE EACH TIME. VERIFIED WITH CAS PRESENT, APPLIED APU B/A TO SUPPLEMENT ECS SYSTER AND CAS WILL EXTINGUISH. VERIFIED WITH CAS PRESENT, APPLLED MINIMAL AMOUNT OF N1 AND CAS WILL EXTINGUISH. VERIFIED WITH CAS PRESENT, TURNED OFF A/L AND CAS WILL EXTINGULSH. THIS INDICATES THAT ALTHOUGH THE AIRCRAFT IS PASSING THE CHECKS WITHIN THE AFM AND AMM, TIIE SYSTEM IS WEAK AND THE ADDITLONAL DEMAND WITH LOW B/A PSI IS ALLOWED THE PRSOVS/DP SWITCHES TO REACT INCORRECTLY, SHUT DOWN THE ENGINES AND REMOVED POWER FROM THE AIRCRAFT. TECHS CONTACTED MCC WITH OUR FINDINGS AND WERE ADVISED TO REPLACE THE LH PYLON PRSOV, RH PYLON PRSOV, AND RH HP PRSOV BASED ON FLEET HISTORY OF WEAK PRSOVS AND THE DP SWITCHES BEING SWAPPED ON THE LAST EVENT. TECHS HAD AIRCRAFT RELOCATED TO HANGAR AND REMOVED THE LH AND RH ENGINE UPPAR AND LOWER COWL AS REQUIRED. PERFORMED A GVI OF THE LH PYLON PRSOV, RH PYLON PROSV, AND RH HP VALVE WITH NO OBVIOUS DEFECTS NOTED. PERFORMED A GVI OF THE LH AND RH DP SWITCHES WITH NO OBVIOUS DEFECTS NOTED. AWAITED PARTS. REMOVED FAULTY LH PYLON PRSOV P/N: 9914520-2 S/N: D2904 AND INSTALLED OVERHAULED PRSV.VALVE P/N: 9914520-2 5/N: D0536 IAW CE6BOA AMM 36-10-10. / REMOVED FAULTY RH PYLON PRSOV P/N: 9914520-2 S/N: D2721 AND INSTALLED THE OVERHAULED PRSOV VALVE P/N: 9914520-2 S/N: D0554 JAW CE680A AMM 36-10-10. REMOVED FAULTY HP PRSOV P/N: 9914520-2 5/N: D2908 AND INSTALLED THE OVERHAULED HP PRSOV P/N: 9914520-2 S/N: D3299 IAW CE680A AMM 36-10-05 TECHS HAD AIRCRAFT RELOCATED TO THE KJAC RAMP TO PERFORM ENGINE RUNS AND OPS CHECKS. POWERED UP AIRCRAFT IAW AFM AND STARTED BOTH THE LH AND RH ENGINES. PERFORMED THE WING/STAB A/I CHECKS IAW CE680A MM 30-10-00 AND 30-15-00 WITH NO DEFECTS NOTED. PERFORMED THE AOM ANTL-ICE CHECK AND STILL RECEIVED THE FAULTY CAS, ALTHOUGH INTERMITTENTLY. TECHS SHUT DOWN ENGINES AND REMOVED POWER FROM THE AIRCRAFT. DUE TO WEATHER RELOCATED AIRCRAFT INTO THE HANGAR. TECHS REMOVED THE LINES COMING OFF THE LH DELTA P SWITCH AND FOUND MINOR AMOUNTS OF DEBRIS. CLEANED ALL CONTAINMENTS FROM LINES AND SWITCH AS ABLE. TECHS REMOVED THE LINES COMING OFF THE RH DELTA P SWITCH AND FOUND MINOR AMOUNTS OF DEBRIS. CLEANED ALL CONTAINMENTS FROM IINES AND SWITCH AS ABLE. CONTACTED MCC WITH FINDINGS. AS THE DRIVER FOR THE CAS MESSAGE AND DUE TO THE FACT THAT THE SWITCHES WERE SWAPPED ON THE LAST EVENT, TECHS WERE ADVISED TO REPLACE THE DELTA P SWITCHES, DUE TO BACKORDERED PARTS, TECHS RETURNED TO SLC TO HELP ON OTHER QS TAILS. CLOSED ALL ACCESS UNTIL TECHS RETURNED ON SITE. / ONCE SHIPPING BECAME AVAILABLE TECHS DISPATCHED FROM KSLC TO KIAC TO MEET THE PARTS. RECEIVED 2 EA SWITCHES IN A NEW CONDITION WITH ALL PAPERWORK MATCHING. REMOVED THE LH AND RH ENGINE UPPER/LOWER COWLS IAW CE680A MM 71-10-05. / REMOVED LH ENGINE DELTA P SWITCH P/N:1153P0104 S/N: 2252 AND INSTALLED NEW SWITCH P/N: 1153P0104 5/N:3008 IAW CEGBOA AMM 36-10-15. REMOVED RH ENGINE DELTA P SWITCH P/N: 1153P0104 S/N:2234 AND INSTALLED NEW SWITCH P/N: 1153P0104 S/N: 3032 IAW CE6BDA AMM 36-10-15. TECHS HAD AIRCRAFT RELOCATED TO THE KIAC RAMP TO PERFORM ENGINE RUNS AND OPS CHECKS. APPLIED POWER AND STARTED THE ENGINES IAW AFM. PERFORMED WING/STAB A/I CHECK IAW CE6S0A MM 30-10-00