SB13C Motor Mount Failure (2016-6-10)

After extensive testing, we have found the root causes of the two in-field failures.

Root cause 1:
Change in geometry Our supplier for machined aluminum components removed a radius on the inner surface of the motor mount. Removal of this radius led to a substantial increase in the stress concentration during flight loading which contributed to the failure. Our supplier changed this feature without approval or notification to Freefly. Freefly also failed to identify the removal of this radius in our incoming quality control inspection.

Root cause 2:

Sub­-optimal thickness Some of the motor mounts shipped during the affected time frame exhibited wall thicknesses that were lower than intended. Freefly did not catch this issue in our incoming quality control process.

Both of the failed motor mounts exhibited the lack of radius and were below nominal thickness. These two issues compounded to cause the accelerated failure of the motor mounts.

All of this testing and investigation has led us to the following solution:

  • Inspect all inbound Alta 8 motor mounts for micro cracks, cracks, or any signs of stress
  • Replace any nonconforming mounts
  • Bond a reinforcement plate into the bottom of each motor mount to strengthen the motor mount
  • Institute a factory service interval for all Altas where customers can send their Alta back to Freefly for inspection

If you have any questions about this bulletin, please contact Freefly Technical Support at

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