Flight modes

The flight mode decides who flies and how: the pilot through the sticks, the autopilot holding what the pilot asks, or the autopilot on its own. CORV GCS shows the current mode in the command bar, coloured by kind, and switches it from the list next to it; the behaviour of each mode is the autopilot’s, described in the ArduPilot documentation linked below for every one.

Colour in the command bar	Kind
■ yellow	Manual — the pilot flies, the autopilot at most stabilises
■ cyan	Assisted — the autopilot holds height, position or attitude while the pilot steers (also every mode not listed otherwise)
■ green	Automatic — mission, autotune, brake
■ orange	Return / land — RTL, Smart RTL, Auto RTL, land, QRTL, QLAND, a sub’s SURFACE

A mode change is a request: the autopilot refuses a mode it cannot fly — most often one that needs a position when it has none — and the list goes back to the current mode with the error. Which switch position selects which mode on the radio is set in SETUP → VEHICLE SETUP → FLIGHT MODES (mode channel and six slots, read from and written to the vehicle) — ArduPilot: flight mode configuration.

Position and the modes that need it

ArduPilot divides its modes into those that need a valid position — a GPS fix, or another position source feeding the EKF — and those that do not. Without a position, only the second group can be flown. The tables below give the requirement as the ArduPilot documentation states it (Copter flight modes, Plane flight modes, Sub modes); “see page” where that list does not.

This is why the GCS has a relative navigation mode: with no GPS at all the autopilot reports no position, and what can still be shown is a position the GCS estimates. Flying the position modes without GPS needs a position source on the vehicle — optical flow, visual odometry, a DVL or USBL on a sub — non-GPS navigation, EKF sources.

Copter

#	Mode	Colour	Needs position	ArduPilot
0	STABILIZE	yellow	no	Stabilize
1	ACRO	yellow	no	Acro
2	ALT_HOLD	cyan	no	Alt Hold
3	AUTO	green	yes	Auto
4	GUIDED	cyan	yes	Guided
5	LOITER	cyan	yes	Loiter
6	RTL	orange	yes	RTL
7	CIRCLE	cyan	yes	Circle
9	LAND	orange	no	Land
11	DRIFT	cyan	yes	Drift
13	SPORT	cyan	no	Sport
14	FLIP	cyan	see page	Flip
15	AUTOTUNE	green	see page	AutoTune
16	POSHOLD	cyan	yes	PosHold
17	BRAKE	green	see page	Brake
18	THROW	cyan	yes	Throw
19	AVOID_ADSB	cyan	see page	ADS-B avoidance
20	GUIDED_NOGPS	cyan	no — attitude targets	Guided
21	SMART_RTL	orange	yes	Smart RTL
22	FLOWHOLD	cyan	optical flow instead	FlowHold
23	FOLLOW	cyan	yes	Follow
24	ZIGZAG	cyan	yes	ZigZag
25	SYSTEMID	cyan	no	System ID
26	AUTOROTATE	cyan	yes (heli)	Autorotation
27	AUTO_RTL	orange	yes	Auto — the mission’s landing sequence
28	TURTLE	cyan	no	Turtle — flips a crashed multirotor back over

The command bar has shortcut buttons for RTL, AUTO and LAND, and TAKEOFF (GUIDED take-off) — see Flight screen.

Plane and QuadPlane

#	Mode	Colour	Needs GPS	ArduPilot
0	MANUAL	yellow	no	Manual
1	CIRCLE	cyan	yes	Circle
2	STABILIZE	yellow	no	Stabilize
3	TRAINING	yellow	no	Training
4	ACRO	yellow	no	Acro
5	FBWA	cyan	no	FBWA
6	FBWB	cyan	no	FBWB
7	CRUISE	cyan	see page	Cruise
8	AUTOTUNE	green	no	AutoTune
10	AUTO	green	yes	Auto
11	RTL	orange	yes	RTL
12	LOITER	cyan	yes	Loiter
13	TAKEOFF	cyan	yes	Takeoff
14	AVOID_ADSB	cyan	see page	ADS-B avoidance
15	GUIDED	cyan	yes	Guided
17	QSTABILIZE	cyan	see page	QStabilize
18	QHOVER	cyan	see page	QHover
19	QLOITER	cyan	see page	QLoiter
20	QLAND	orange	see page	QLand
21	QRTL	orange	see page	QRTL
22	QAUTOTUNE	cyan	see page	QAutoTune
23	QACRO	cyan	see page	QAcro
24	THERMAL	cyan	yes	Thermal
25	LOITER_ALT_QLAND	cyan	see page	QuadPlane modes
26	AUTOLAND	cyan	yes	Autoland

Without GPS a plane can still be flown in the manual and stabilised modes; the GCS can then only estimate its position from airspeed and heading — see dead reckoning. Measured in SITL, an ArduPlane that never had a GPS does not start its EKF at all (DCM only), as also discussed on the ArduPilot forum.

Rover and boat

#	Mode	Colour	ArduPilot
0	MANUAL	yellow	Manual
1	ACRO	yellow	Acro
3	STEERING	cyan	Steering
4	HOLD	cyan	Hold
5	LOITER	cyan	Loiter (boats)
6	FOLLOW	cyan	Follow
7	SIMPLE	cyan	Simple
8	DOCK	cyan	Dock
9	CIRCLE	cyan	Circle
10	AUTO	green	Auto
11	RTL	orange	RTL
12	SMART_RTL	orange	Smart RTL
15	GUIDED	cyan	Guided

The Rover control modes page gives the requirements of each.

Sub (ROV)

#	Mode	Colour	Needs	ArduPilot
0	STABILIZE	yellow	—	Sub modes
1	ACRO	yellow	—	Sub modes
2	ALT_HOLD	cyan	depth sensor	Sub modes
3	AUTO	green	position and depth	Sub modes
4	GUIDED	cyan	position and depth	Sub modes
7	CIRCLE	cyan	position and depth	Sub modes
9	SURFACE	orange	—	Sub modes
16	POSHOLD	cyan	position and depth	Sub modes
19	MANUAL	yellow	—	Sub modes
20	MOTOR_DETECT	cyan	—	Sub modes — finds each thruster’s direction
21	SURFTRAK	cyan	rangefinder	Sub modes — holds the distance above the bottom

ALT_HOLD is depth hold. A sub gets a position from a DVL or an underwater positioning system (USBL), not from GPS; without one only MANUAL, STABILIZE, ACRO, ALT_HOLD, SURFACE and (with a downward rangefinder) SURFTRAK are available. A real BlueROV2 with a USBL, replayed in the GCS, flew POSHOLD at 20 m — see a real dive. ArduSub acts when the pilot input from its GCS stops for a few seconds (pilot control failsafe) — in the simulator runs for this guide it disarmed the vehicle; the other sub failsafes are on the failsafes page.

INAV and Betaflight

Over MSP the GCS resolves INAV’s active modes to one name: MANUAL, ACRO, ANGLE, HORIZON, ALTHOLD, POSHOLD, COURSE HOLD, CRUISE, WAYPOINT, RTH, FAILSAFE. They are selected on the radio, as INAV expects; the INAV navigation modes page describes them. Betaflight has no navigation modes.