Some owners of SOCATA’s new TBM 850 single-engine turboprop may be facing extended grounding following the company’s service alert on cracked compressor drive shafts. Alert SB70-161 was released June 20 after a report of a driveshaft shear failure on a TBM 850. The June alert limited drive shafts to 80 flight hours before replacement while the company works to complete the design and certification of an improved drive assembly. After further review, however, an amendment was released this week that limits the hours allowed on the drive shaft. Stress cracks have been found in the shafts that exceed what was originally anticipated in the first service bulletin. Some aircraft are required to have immediate shaft replacement while others will have their shaft total time reduced to 35 or 40 hours, depending on the aircraft serial number. The latest production aircraft and the replacement shafts sent by the company will retain the original 80 hours total time because of the additional magnaflux inspections during their manufacture.

SOCATA has completed the design of a new drive assembly and is currently fabricating test and evaluation parts. The new compressor drive assemblies are anticipated to be available by mid-October 2008. More information from SOCATA concerning this service bulletin is coming and AVweb will follow the story as it develops.