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Improve flight termination docs

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Hamish Willee
2025-07-24 10:50:30 +10:00
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docs/en/advanced_config/flight_termination.md
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# Flight Termination Configuration
The _Flight termination_ [failsafe action](../config/safety.md#failsafe-actions) may be triggered by a [safety check](../config/safety.md) (e.g. RC Loss, geofence violation, etc. on any vehicle type or in any flight mode), by the [Failure Detector](../config/safety.md#failure-detector), or manually by toggling a termination switch mapped to an RC channel (see [RC_MAP_TERM_SW](../advanced_config/parameter_reference.md#RC_MAP_TERM_SW)).
The _Flight termination_ [failsafe action](../config/safety.md#failsafe-actions) irreversibly turns off controllers and sets PWM values to their parameter configured failsafe values.
::: info
Flight termination may also be triggered from a ground station or companion computer using the MAVLink [MAV_CMD_DO_FLIGHTTERMINATION](https://mavlink.io/en/messages/common.html#MAV_CMD_DO_FLIGHTTERMINATION) command.
This is sent, for example, when you call the [MAVSDK Action plugin](https://mavsdk.mavlink.io/main/en/cpp/api_reference/classmavsdk_1_1_action.html#classmavsdk_1_1_action_1a47536c4a4bc8367ccd30a92eb09781c5) `terminate()` or `terminate_async()` methods.
Flight termination differs from the [Kill action](../config/safety.html#kill-switch) in that it is permanent until after reboot.
:::
::: warning
This is _not_ an independent _Flight Termination System_.
If power is lost or if the autopilot crashes completely, the failsafe devices will not be triggered.
:::
## Overview
### Termination Triggers
Termination may be triggered by:
- [Safety checks](../config/safety.md) for RC Loss, geofence violation, and so on (on any vehicle type or in any flight mode).
- [Failure Detector](../config/safety.md#failure-detector) trigger
- RC termination switch (mapped to an RC channel using [RC_MAP_TERM_SW](../advanced_config/parameter_reference.md#RC_MAP_TERM_SW)).
- The MAVLink [MAV_CMD_DO_FLIGHTTERMINATION](https://mavlink.io/en/messages/common.html#MAV_CMD_DO_FLIGHTTERMINATION) MAVLink command from a GCS or companion computer (see [MAVLink Trigger](#mavlink-trigger) below).
There is no way to recover from flight termination.
After triggering you should unplug the battery as soon as possible.
You will need to reboot/power cycle the vehicle before it can be used again.
### Termination Actions
When _Flight termination_ is activated, PX4 simultaneously turns off all controllers and sets all PWM outputs to their failsafe values.
Depending on what devices are connected, the PWM failsafe outputs can be used to:
@@ -17,10 +38,6 @@ Depending on what devices are connected, the PWM failsafe outputs can be used to
- Trigger an inflatable device like an airbag.
- Trigger an alarm.
There is no way to recover from flight termination.
After triggering you should unplug the battery as soon as possible.
You will need to reboot/power cycle the vehicle before it can be used again.
:::tip
PX4 does not know what safety devices are attached - it just applies a predefined set of PWM values to its outputs.
:::
@@ -30,11 +47,6 @@ Failsafe values are applied to all outputs on termination.
There is no way to configure independent time-based (or other) triggering of the motors or specific safety devices.
:::
::: info
This is _not_ an independent _Flight Termination System_.
If power is lost or if the autopilot crashes completely, the failsafe devices will not be triggered.
:::
## Hardware Configuration
Any _safety device(s)_ (e.g. a [parachute](../peripherals/parachute.md)) that can be triggered by changing a PWM value can be used, and may be connected to any free PWM port (both MAIN and AUX).
@@ -74,6 +86,12 @@ Flight termination via ATS only works if `drivers/pwm_input` is included in the
If not, you need to add it manually to your board configuration using [boardconfig](../hardware/porting_guide_config.md#px4-menuconfig-setup).
:::
## MAVLink Trigger
The [MAV_CMD_DO_FLIGHTTERMINATION](https://mavlink.io/en/messages/common.html#MAV_CMD_DO_FLIGHTTERMINATION) command can be used to trigger Flight termination from a ground station or companion computer.
This is sent, for example, when you call the [MAVSDK Action plugin](https://mavsdk.mavlink.io/main/en/cpp/api_reference/classmavsdk_1_1_action.html#classmavsdk_1_1_action_1a47536c4a4bc8367ccd30a92eb09781c5) `terminate()` or `terminate_async()` methods.
## Logic Diagram
The diagram below shows the logical flow around flight termination.