What was found
CREW WRITE UP. WITH BOTH PACKS ON WITH ENGINES RUNNING, THE COCKPIT IS VERY LOUD ON THE GROUND AND IN THE AIR. THE EXCESSIVE NOISE SEEMS TO COME FROM AIR FLOW FROM THE PACK. THIS IS A REPEAT WRITE UP FOR MANY YEARS. FLIGHT DECK NOISE LEVEL MEASUREMENT CHECK CARRIED OUT IAW AMM 21-00-00-6 RESULT 75DBS. CARRIED OUT TROUBLESHOOTING OF FLIGHT DECK NOISE IAW AMM 21-00- 00-6. RECIRCULATION AIR CHECK VALVE SATIS, RECIRCULATION FAN FILTER SATIS, CONDITIONED AIR BYPASS VALVE SATIS, BOTH PACKS VERIFIED IN LOW FLOW WITH BOTH ENGINES AT IDLE WITH APU BLEED OFF AND RECIRCULATION FAN ON. FOUND NO ORIFICE REDUCER PLATE INSTALLED AT EITHER BS 585 OR BS 883. FABRICATED ORIFICE PLATE IAW VT MOBILE AEROSPACE ENGINEERING INC DRAWING NUMBER 11812440. SEE ERS 18-04689 FOR ENGINEERING CORRESPONDENCE. INSTALLED ORIFICE PLATE AT BS 585 IAW AMM 21-20-01-4. CARRIED OUT ORIFICE INSTALLATION TEST IAW AMM 21-20-01-4. CARRIED FLIGHT DECK NOISE LEVEL MEASUREMENT CHECK IAW AMM 21-00-00-6 RESULT 67DBS. P/N 11812440-0450-0230