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841bb40365
Give NAVIGATION_STATE_DESCEND its own MAVLink custom_mode and advertise it so ground stations stop displaying it as Land. --------- Signed-off-by: Elisa Ferrara <elisa.ferrara@auterion.com>
38 lines
2.2 KiB
Markdown
38 lines
2.2 KiB
Markdown
# Descend Mode (Multicopter)
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_Descend_ is a [failsafe](../config/safety.md) fallback mode.
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It is activated automatically by PX4 and cannot be selected by the pilot. It only appears as a status label.
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The vehicle descends open-loop: it keeps its attitude and reduces altitude, but does not control its horizontal position, so it drifts with the wind.
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It is the last resort used when the vehicle must come down but has no valid position estimate for a controlled descent.
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::: info
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- Mode is automatic and cannot be selected by the user.
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- Requires only attitude, so it works without a position (or even altitude) estimate.
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- The descent rate is set by [MPC_LAND_SPEED](../advanced_config/parameter_reference.md#MPC_LAND_SPEED).
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:::
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## When It Occurs
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Descend is the bottom of the failsafe chain (`Hold → Return → Land → Descend`).
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PX4 falls through to it whenever a failsafe needs to bring the vehicle down or hold position but the position estimate is missing, so none of the higher options can run. For example:
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- Losing the position estimate while landing, e.g. GNSS fails during [Land](../flight_modes_mc/land.md): the vehicle keeps descending, but now open-loop as _Descend_.
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- Losing the position estimate in [Hold](../flight_modes_mc/hold.md), [Mission](../flight_modes_mc/mission.md) or [Return](../flight_modes_mc/return.md): with no position to hold, fly to, or return with, the failsafe escalates down to _Descend_.
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- A Return or Land failsafe (from manual control loss, GCS/data link loss, low battery, geofence breach, …) triggered while no valid position estimate is available: Return and Land can't run, so it degrades to _Descend_.
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## Exiting Descend
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Descend ends when either:
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- the failsafe condition is resolved (e.g. the position estimate recovers), and the vehicle returns to its previous mode; or
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- the pilot takes over by switching to a manual mode ([Position](../flight_modes_mc/position.md), [Altitude](../flight_modes_mc/altitude.md) or [Stabilized](../flight_modes_mc/manual_stabilized.md)). On a multicopter, moving the sticks does this [by default](../flight_modes_mc/land.md#MAN_OVERRIDE_SPD).
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## See Also
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- [Descend Mode (FW)](../flight_modes_fw/descend.md)
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- [Land Mode (MC)](../flight_modes_mc/land.md)
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- [Safety (Failsafes)](../config/safety.md)
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