SB005 Alta X – Improper Mission Throttle Command (11/05/21)

Date Released: Nov 2nd 2021

Subject: Improper Mission Throttle Command resulting in aircraft descent

Effectivity: All Alta X

Require Action: Modify workflow

Update: January 2022

A hotfix has been implemented in Software Release 1.3.2 and all subsequent software releases. This is a critical software release that fixes a potential failure mode that can be triggered during auto missions and/ or when RTL is engaged. It is required for all Alta X users to upgrade to maintain safe flight operations.

The following is reference information only, the following actions and recommendations are no longer necessary after the firmware update mentioned above.


This service bulletin is being issued to alert all Alta X pilots of an in-flight failure that 2 Freefly customers have experienced. One instance resulted in an Alta X crash.


2 customers have reported a momentary glitch that reduces throttle setpoint upon switching from position flight mode to mission flight mode. During our investigation we believe the issue is caused by 2 main errors:

  1. There is an error in the PX4 firmware that incorrectly acts on an invalid setpoint when entering mission mode, which reduces throttle to 0 momentarily
  2. There appear to be some microSD cards that exacerbate this issue by writing / reading slowly. This is the microSD card found in the flight controller. The SDcard read delay causes the invalid setpoint to remain active much longer, resulting in aircraft not holding position correctly.


Some key points to convey regarding this issue:

  • This issue has only been observed when switching to mission mode in flight
    • Launching mission mode from the ground has never show this issue (or any similar issue)
  • This issue will not impact manual, altitude, or GPS based flight modes
  • Freefly is creating an updated firmware that will fix the root cause of this problem


  1. Do not switch to mission mode in flight, launch missions from the ground until Freefly releases an updated firmware fix for this issue

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