docs: add docs on new guided course mode

docs/en/SUMMARY.md

@@ -76,6 +76,7 @@
     - [Takeoff Mode (FW)](flight_modes_fw/takeoff.md)
     - [Land Mode (FW)](flight_modes_fw/land.md)
     - [Hold Mode (FW)](flight_modes_fw/hold.md)
+    - [Guided Course Mode (FW)](flight_modes_fw/guided_course.md)
     - [Mission Mode (FW)](flight_modes_fw/mission.md)
     - [Return Mode (FW)](flight_modes_fw/return.md)
     - [Offboard Mode (FW)](flight_modes_fw/offboard.md)

docs/en/flight_modes_fw/guided_course.md

@@ -0,0 +1,74 @@
+# Guided Course Mode (Fixed-Wing)
+
+<img src="../../assets/site/position_fixed.svg" title="Position required (e.g. GPS)" width="30px" />
+
+_Guided Course mode_ maintains a constant ground track (course), altitude, and airspeed without any manual stick input.
+The operator controls the vehicle entirely via [GCS commands](#in-flight-commands), making it the guided equivalent of [Position mode](../flight_modes_fw/position.md).
+
+:::tip
+This mode is suited to situations where an operator wants to guide a fixed-wing vehicle from a GCS without manual control.
+:::
+
+::: info
+
+- Requires a horizontal velocity estimate (e.g. GPS/dead-reckoning).
+  Course commands will be rejected if the velocity estimate is unavailable.
+- Manual control input is ignored.
+
+<!-- https://github.com/PX4/PX4-Autopilot/blob/main/src/modules/commander/ModeUtil/mode_requirements.cpp -->
+
+:::
+
+## Overview
+
+On activation, the vehicle captures its current velocity over ground vector as the initial course bearing and holds altitude and airspeed from the moment of activation.
+The vehicle then flies that course indefinitely until the operator issues a new command.
+
+There is no waypoint sequencing or autonomous path planning: the GCS guides the vehicle in real time by sending individual commands.
+
+## Supported Commands
+
+The following commands are accepted while in Guided Course mode:
+
+| Command                         | Effect                                                                                                                          |
+| ------------------------------- | ------------------------------------------------------------------------------------------------------------------------------- |
+| [MAV_CMD_GUIDED_CHANGE_HEADING] | Set a new course bearing (degrees, 0 = north) with `HEADING_TYPE = 0`. Rejected if horizontal velocity estimate is unavailable. |
+| [MAV_CMD_DO_CHANGE_ALTITUDE]    | Set a new target altitude (AMSL, metres).                                                                                       |
+| [MAV_CMD_DO_CHANGE_SPEED]       | Set a new equivalent airspeed via param2 (m/s). If param2 ≤ 0, the default cruise speed is restored.                            |
+
+[MAV_CMD_GUIDED_CHANGE_HEADING]: https://mavlink.io/en/messages/common.html#MAV_CMD_GUIDED_CHANGE_HEADING
+[MAV_CMD_DO_CHANGE_ALTITUDE]: https://mavlink.io/en/messages/common.html#MAV_CMD_DO_CHANGE_ALTITUDE
+[MAV_CMD_DO_CHANGE_SPEED]: https://mavlink.io/en/messages/common.html#MAV_CMD_DO_CHANGE_SPEED
+
+## Technical Description
+
+The navigator mode (`course.cpp`) sets a position setpoint with `course` (ground track bearing) and `alt` fields populated, and `yaw = NAN`.
+
+The fixed-wing mode manager (`FixedWingModeManager`) detects the finite `course` field and bypasses normal waypoint sequencing, calling `navigateBearing()` from the directional guidance library to compute lateral acceleration and course setpoints.
+Longitudinal control targets the altitude and airspeed from the setpoint.
+
+## Failsafe Behaviour
+
+Guided Course is classified as an `AUTO` mode for failsafe purposes.
+The following failsafe exception parameters apply:
+
+| Parameter                                                                  | Bit            | Effect when set                                   |
+| -------------------------------------------------------------------------- | -------------- | ------------------------------------------------- |
+| [COM_RCL_EXCEPT](../advanced_config/parameter_reference.md#COM_RCL_EXCEPT) | 1 (Auto modes) | RC loss does not trigger a failsafe in this mode. |
+| [COM_DLL_EXCEPT](../advanced_config/parameter_reference.md#COM_DLL_EXCEPT) | 1 (Auto modes) | GCS connection loss does not trigger a failsafe.  |
+
+:::warning
+Since Guided Course is driven entirely by GCS commands, operators should carefully consider the datalink loss failsafe setting (`COM_DLL_EXCEPT` bit 1).
+If the GCS link drops, the vehicle will continue on its last commanded course indefinitely.
+It is strongly recommended to either leave the datalink failsafe active or ensure a secondary safety mechanism (e.g. geofence, battery failsafe) is in place.
+:::
+
+## Parameters
+
+| Parameter                                                                  | Description                                                                                           |
+| -------------------------------------------------------------------------- | ----------------------------------------------------------------------------------------------------- |
+| [FW_AIRSPD_TRIM](../advanced_config/parameter_reference.md#FW_AIRSPD_TRIM) | Default cruise airspeed used on activation and when `MAV_CMD_DO_CHANGE_SPEED` is sent with value ≤ 0. |
+| [FW_AIRSPD_MIN](../advanced_config/parameter_reference.md#FW_AIRSPD_MIN)   | Minimum airspeed. Commanded airspeed is clamped to this value.                                        |
+| [FW_AIRSPD_MAX](../advanced_config/parameter_reference.md#FW_AIRSPD_MAX)   | Maximum airspeed. Commanded airspeed is clamped to this value.                                        |
+| [COM_RCL_EXCEPT](../advanced_config/parameter_reference.md#COM_RCL_EXCEPT) | RC loss failsafe exceptions bitmask. Bit 1 covers all auto modes including Guided Course.             |
+| [COM_DLL_EXCEPT](../advanced_config/parameter_reference.md#COM_DLL_EXCEPT) | Datalink loss failsafe exceptions bitmask. Bit 1 covers all auto modes including Guided Course.       |

docs/en/flight_modes_fw/index.md

@@ -39,6 +39,8 @@ Airspeed is actively controlled if an airspeed sensor is installed in any autono
 - [Hold](../flight_modes_fw/hold.md) — Vehicle circles around the GPS hold position at the current altitude.
   The mode can be used to pause a mission or to help regain control of a vehicle in an emergency.
   It can be activated with a pre-programmed RC switch or the QGroundControl Pause button.
+- [Guided Course](../flight_modes_fw/guided_course.md) — Vehicle maintains a constant ground track, altitude, and airspeed.
+  The operator commands course, altitude, and airspeed changes in real time from the GCS. Manual stick input is ignored.
 - [Return](../flight_modes_fw/return.md) — Vehicle flies a clear path to land at a safe location.
   By default the destination is a mission landing pattern.
   The mode may be activated manually (via a pre-programmed RC switch) or automatically (i.e. in the event of a failsafe being triggered).