Fleet Team Digest 737NG-FTD-21-02001
Description:
Operators have indicated the 737NG flight deck produces a higher level of noise than the 737 Classic flight deck. Boeing is actively working on reducing the noise generated in the flight deck by reworking the Environmental Control System including the recirculation fan noise and nose section boundary layer noise.
Portions of PRR 38592 have been implemented beginning at line number 1552, delivered 12 August 2004 (see incorporation line numbers under "Applicability" above). Service Bulletin 737-25-1543 which incorporates the intent of the PRR was released 9 November 2012.
PRR 38955 has been implemented beginning at line number 3770 delivered Sept 2011. Service Bulletin 737-21-1178 which will incorporate the intent of the PRR is anticipated for release Jan 2013.
Status
PRR 38592 "Flight Deck Noise Reduction" has been committed for production airplanes:
Part A - Add damping panels on skin interior between frames
Part B - Revise overhead lining for new ECS plenum
Add vortex generators to exterior skin below the #1 window
Add gap fill material to fwd edge of #2 window
New muffler build process to reduce noise
Re-route flex hose to reduce bends
Redesign plenum to reduce noise
Part C - Retrofit Service Bulletin - SB 737-25-1543
Part D - Increase density of insulation blanket.
PRR 38955 "Flight Deck Air Distribution Improvements" has been committed for production airplanes:
Part A - Overhead and shoulder plenums modified to reduce noise in the flight deck.
Part B - Retrofit Service Bulletin - SB 737-21-1178
Interim Action
Service Letter 737-SL-21-067, notified operators of a new muffler, Boeing P/N 65C25629-94 which was developed to eliminate the collapsed lining material. Additionally, the new muffler includes enhanced noise reduction features.
The original flight deck muffler, Boeing P/N 65C25629-85 is a component of existing line replaceable unit (LRU) muffler assemblies. The new muffler, Boeing P/N 65C25629-94 will be part of new LRU muffler assemblies. Boeing does not have retrofit solutions for installing the new muffler in the existing muffler assembly, but the existing muffler assemblies may be replaced with the new muffler assemblies as noted in the service letter.
Final Action
Part A, Part B and Part D of PRR 38592 have been incorporated in production at airplane line positions 1552, 1650, and 1696, delivered Aug 2004, Feb 2005 and April 2005 respectively.
Service Bulletin 737-25-1543 was released 9 November 2012 (Part C of PRR).
Part A of PRR 38955 (flight deck shoulder plenum and ducting redesign) was installed in production at line position 3770, delivered Sept 2011.
Service Bulletin 737-21-1178 will be published for incorporation of the modifications equivalent to production for Flight Deck Noise Reduction (Part B of PRR). ECD is late Jan 2013.