Ethiopian airliner down in Africa

[Chronus]

Originally Posted by Organfreak

Sorry, link is bad. Looks as if it's a local file on your puter.

Apologies for that, it is a pdf file on www.eaton.eu

Here is the slide :
Boeing 737NG • Improve field reliability of the Horizontal Stabilizer Trim Motor (STM) • Solder joint fatigue of the memory chip • 6355C0001-01 to 6355C0001-02 5 © 2018 Eaton. All Rights Reserved.. Background Part history • Eaton has been the provider of the Stabilizer Trim Motor used on the Boeing 737NG since 1996. • 6355B0001-02/-03:1996 - 2003 • 6355C0001-01: 2003 - 2017 • 6355C0001-02: 2017 - Present • 6355D0001-01: 2016 - Present • Unique to the 737MAX and not interchangeable with 6355B/C configurations 6 © 2018 Eaton. All Rights Reserved.. Background • Stabilizer Trim Motor (STM) exceeds Boeing’s reliability requirements. However, in partnership with Boeing and using Eaton’s continuous improvement process and operator feedback, design improvements have been made to further improve field reliability. • Primary failure mode is solder joint fatigue of the non-volatile memory (NVM) chip due to a combination of uncontrolled environmental conditions causing bending, vibration and thermal expansion stresses. • Eaton implemented a shimming procedure that will ensure the control printed wire assembly (PWA) is held flat, so that all component leads, including the NVM, are free from mechanical bending stress. This change is identified on 6355C0001-01 units as Modification 9 (“Mod 9”). • Boeing has performed an in-depth analysis of the Horizontal Stabilizer Trim System Wiring design to include ships wiring, switches and production breaks and splices. The results of the Boeing Study show that operators may reduce the No Fault Found test results for the STM by checking the airplane wiring and switching components prior to removal. 7 © 2018 Eaton. All Rights Reserved.. Solution • Joint investigation into the STM’s field reliability with Boeing, along with lessons learned from 737MAX qualification, have yielded design improvements to the Control PWA. • Modifications to the NVM chip package which is significantly more robust to vibration and thermal expansion. • Control PWA changes include NVM component replacement, component land pattern optimization, component height spacers, copper balancing of the PWB, reduction of hand soldering operations and addressing potential obsolescence concerns. • An upgrade of a 6355C0001-01 to a 6355C0001-02 will require a new Control PWA (the PWA itself can not be upgraded). • Long term lab testing of the 6355C0001-02 shows that the failure mode of solder joint fatigue of the Non-Volatile Memory (