Pre-Arm Safety Checks¶

ArduPilot includes a suite of Pre-arm Safety Checks which will prevent the vehicle from arming its propulsion system if any of a fairly large number of issues are discovered before movement including missed calibration, configuration or bad sensor data. These checks help prevent crashes or fly-aways but some can also be disabled if necessary.

Warning

Never disable the arming checks (ie ARMING_CHECK not = “1”, except for bench testing. Always resolve any prearm or arming failures BEFORE attempting to fly. Doing otherwise may result in the loss of the vehicle.

Recognising which Pre-Arm Check has failed using the GCS¶

The pilot will notice a pre-arm check failure because he/she will be unable to arm the vehicle and the notification LED, if available, will be flashing yellow. To determine exactly which check has failed:

Connect the Autopilot to the ground station using a USB cable or Telemetry.
Ensure the GCS is connected to the vehicle (i.e. on Mission Planner and push the “Connect” button on the upper right).
Turn on your radio transmitter and attempt to arm the vehicle (regular procedure is using throttle down, yaw right or via an RCx_OPTION switch)
The first cause of the Pre-Arm Check failure will be displayed in red on the HUD window

Pre-arm checks that are failing will also be sent as messages to the GCS while disarmed, about every 30 seconds. If you wish to disable this and have them sent only when an attempt arm fails, then set the ARMING_OPTIONS bit 1 (value 1).

Pre-Arm Failure Messages (All vehicle types)¶
Message	Cause	Solution
3D Accel calibration needed	Accelerometer calibration has not been done	Complete the accel calibration
Accels calibrated requires reboot	Autopilot must be rebooted after accel calibration	Reboot autopilot
Accels inconsistent	Two accelerometers are inconsistent by 0.75 m/s/s	Re-do the accel calibration. Allow autopilot to warm-up and reboot. If failure continues replace autopilot
ADSB out of memory	Autopilot has run out of memory	Disable features or replace with a higher powered autopilot
Accels not healthy	At least one accelerometer is not providing data	Reboot autopilot. If failure continues replace autopilot
AHRS: not using configured AHRS type	EKF3 is not ready yet and vehicle is using DCM	If indoors, go outside. Ensure good GPS lock. Check for misconfiguration of EKF (see AHRS_EKF_TYPE)
AHRS: waiting for home	GPS has not gotten a fix	If indoors, go outside. Ensure compass and accelerometer calibrations have been completed. Eliminate radio-frequency sources that could interfere with the GPS
Airspeed 1 not healthy	Autopilot is unable to retrieve data from sensor	Check the physical connection and configuration
AP_Relay not available	Parachute misconfigured	Parachute is controlled via Relay but the relay feature is missing. Custom build server was probably used, rebuild with relay enabled
Auxiliary authorisation refused	External system has disallowed authorisation	Check external authorisation system
Batch sampling requires reboot	Batch sampling feature requires Autopilot reboot	Reboot autopilot or check Batch sampling configuration
Battery below minimum arming capacity	Battery capacity is below BATT_ARM_MAH	Replace battery or adjust BATT_ARM_MAH
Battery below minimum arming voltage	Battery voltage is below BATT_ARM_VOLT	Replace battery or adjust BATT_ARM_VOLT
Battery capacity failsafe critical >= low	Battery failsafe misconfiguration	Check BATT_LOW_MAH is higher than BATT_CRT_MAH
Battery critical capacity failsafe	Battery capacity is below BATT_CRT_MAH	Replace battery or adjust BATT_CRT_MAH
Battery critical voltage failsafe	Battery voltage is below BATT_CRT_VOLT	Replace battery or adjust BATT_CRT_VOLT
Battery low capacity failsafe	Battery capacity is below BATT_LOW_MAH	Replace battery or adjust BATT_LOW_MAH
Battery low voltage failsafe	Battery voltage is below BATT_LOW_VOLT	Replace battery or adjust BATT_LOW_VOLT
Battery unhealthy	Battery is not providing data	Check battery monitors physical connect and configuration
Battery voltage failsafe critical >= low	Battery failsafe misconfiguration	Check BATT_LOW_VOLT is higher than BATT_CRT_VOLT
BendyRuler OA requires reboot	Object avoidance config change requires reboot	Reboot autopilot. See Object Avoidance configuration
Board (Xv) out of range 4.3-5.8v	Board voltage below BRD_VBUS_MIN or too high	Check power supply. If powering via USB plug in a battery or replace USB cable
BTN_PINx=y invalid	Button misconfigured	BTNx_PIN is set to an invalid value. Check Button setup instructions
BTN_PINx=y, set SERVOz_FUNCTION=-1	Button misconfigured	Set SERVOz_FUNCTION to -1
Can’t check rally without position	EKF does not have a position estimate yet	Wait or move to location with better GPS reception
Check fence	Fence feature has failed to be initialised	Reboot autopilot
Check mag field (xy diff:x>875)	Compass horiz field strength is too large or small	Relocate vehicle away from metal in the environment. Move compass away from metal in the frame. repeat compass calibration. Disable internal compass.
Check mag field (z diff:x>875)	Compass vert field strength is too large or small	Relocate vehicle away from metal in the environment. Move compass away from metal in the frame. repeat compass calibration. Disable internal compass.
Check mag field: x, max y, min z	Compass field strength is too large or small	Relocate vehicle away from metal in the environment. Move compass away from metal in the frame. repeat compass calibration. Disable internal compass.
Chute has no channel	Parachute misconfigured	Parachute is controlled using PWM but no servo output function has been configured (e.g. need SERVOx_FUNCTION = 27). see Parachute setup instructions
Chute has no relay	Parachute misconfigured	Parachute is controlled via Relay but no relay output has been configured. see Parachute setup instructions
Chute is released	Parachute has been released	Reboot autopilot
Compass calibrated requires reboot	Autopilot must be rebooted after compass cal	Reboot autopilot
Compass calibration running	Compass calibration is running	Complete or cancel the compass calibration
Compass not healthy	At least one compass is not providing data	Check compass’s connection to autopilot and configuration
Compass offsets too high	Compass offset params are too large	Relocate compass away from metal in the frame and repeat compass calibration. Disable internal compass. Increase COMPASS_OFFS_MAX.
Compasses inconsistent	Two compasses angles or field strength disagree	Check compass orientations (e.g. COMPASS_ORIENT). Move compass away from metal in the frame. repeat compass calibration. Disable internal compass.
CrashDump data detected	Crash Dump data has been logged	A CPU crash has occurred and data logged. Plane is probably unsafe to fly! See CRASH DUMP
Dijkstra OA requires reboot	Object avoidance config change requires reboot	Reboot autopilot. See Object Avoidance configuration
Disarm Switch on	Disarm auxiliary switch is in the high position	Move Disarm switch to the low position or check auxiliary functions setup
Downloading logs	Vehicle cannot be armed while logs are downloading	Wait until logs are downloaded, cancel download or reboot autopilot
DroneCAN: Duplicate Node x../y!	DroneCAN sees same node ids used by two devices	Clear DroneCAN DNS server by setting CAN_D1_UC_OPTION = 1 and reboot
DroneCAN: Failed to access storage!	Possible hardware issue	Reboot autopilot
DroneCAN: Failed to add Node x!	DroneCAN could not init connection to a device	Check sensor’s physical connection and power supply
DroneCAN: Node x unhealthy!	A DroneCAN device is not providing data	Check sensor’s physical connection and power supply
Duplicate Aux Switch Options	Two auxiliary function switches for same feature	Check auxiliary function setup. Check for RCx_OPTION parameters with same values
EKF3 Roll/Pitch inconsistent by x degs	Roll or Pitch lean angle estimates are inconsistent	Normally due to EKF3 not getting good enough GPS accuracy, but could be due to other sensors producing errors. Go outdoors, wait or reboot autopilot.
EKF3 waiting for GPS config data	automatic GPS configuration has not completed	Check GPS connection and configuration especially if using DroneCAN GPS
EKF3 Yaw inconsistent by x degs	Yaw angle estimates are inconsistent	Wait or reboot autopilot
Failed to open mission.stg	Failed to load mission from SD Card	Check SD card. Try to re-save mission to SD card
Fence requires position	If fences are enabled, position estimate required	Wait or move vehicle to a location with a clear view of the sky. Reduce sources of radio-frequency interference
FENCE_ALT_MAX < FENCE_ALT_MIN	FENCE_ALT_MAX must be greater than FENCE_ALT_MIN	Increase FENCE_ALT_MAX or lower FENCE_ALT_MIN
FENCE_MARGIN is less than FENCE_RADIUS	FENCE_MARGIN must be larger than FENCE_RADIUS	Increase FENCE_RADIUS or reduce FENCE_MARGIN
FENCE_MARGIN too big	FENCE_ALT_MAX - FENCE_ALT_MIN < 2x FENCE_MARGIN	Decrease FENCE_MARGIN or increase difference between FENCE_ALT_MAX and FENCE_ALT_MIN
Fences enabled, but none selected	Fences are enabled but none are defined	Disable some or all fences using FENCE_ENABLE or FENCE_TYPE or define the missing fences
Fences invalid	Polygon fence is invalid	Check polygon fence does not have overlapping lines
FETtec: Invalid motor mask	FETtec misconfiguration	See FETtec configuration
FETtec: Invalid pole count x	FETtec misconfiguration	See FETtec configuration
FETtec: No uart	FETtec misconfiguration	See FETtec configuration
FETtec: Not initialised	FETtec ESCs are not communicating with autopilot	See FETtec configuration
FETtec: x of y ESCs are not running	FETtec ESCs are not spinning	See FETtec configuration
FETtec: x of y ESCs are not sending telem	FETtec ESCs are not communicating with autopilot	See FETtec configuration
FFT calibrating noise	FFT Harmonic Notch analysis has not completed	Wait until In-Flight FFT analysis completes
FFT config MAXHZ xHz > yHz	FFT Harmonic Notch misconfiguration	See In-Flight FFT Harmonic Notch Setup completes
FFT self-test failed, max error Hz	FFT Harmonic Notch failed	See In-Flight FFT Harmonic Notch Setup completes
FFT still analyzing	FFT Harmonic Notch analysis has not completed	Wait until In-Flight FFT analysis completes
FFT: calibrated xHz/xHz/xHz	FFT Harmonic Notch issue	See In-Flight FFT Harmonic Notch Setup completes
FFT: resolution is xHz, increase length	FFT Harmonic Notch misconfiguration	See In-Flight FFT Harmonic Notch Setup completes
Generator: Not healthy	Generator is not communicating with autopilot	Check generator configuration
Generator: No backend driver	Firmware does not include seelected generator	Build version of firmware with desired generator using custom.ardupilot.org
GPS and AHRS differ by Xm	GPS and EKF positions differ by at least 10m	Wait until GPS quality improves. Move vehicle to a location with a clear view of the sky. Reduce sources of radio-frequency interference
GPS blending unhealthy	At least one GPS is not providing good data	Move vehicle to a location with a clear view of the sky. Reduce sources of radio-frequency interference. Check GPS blending configuration
GPS Node x not set as instance y	DroneCan GPS configuration error	Check GPS1_CAN_NODEID and GPS2_CAN_NODEID
GPS positions differ by Xm	Two GPSs reported positions differ by 50m or more	Wait until GPS quality improves. Move vehicle to a location with a clear view of the sky. Reduce sources of radio-frequency interference
GPS x still configuring this GPS	Automatic GPS configuration has not completed	Wait until configuration completes. Check GPS connection and configuration especially if using DroneCAN GPS
GPS x: Bad fix	GPS does not have a good lock	Move vehicle to a location with a clear view of the sky. Reduce sources of radio-frequency interference
GPS x: not healthy	GPS is not providing data	Check GPSs physical connection to autopilot and configuration
GPS x: primary but TYPE 0	Primary GPS has not been configured	Check GPS_PRIMARY and confirm corresponding GPS1_TYPE or GPS2_TYPE matches type of GPS used
GPS x: was not found	GPS disconnected or incorrectly configured	Check GPSs physical connection to autopilot and configuration
GPSx yaw not available	GPS-for-yaw configured but not working	Move to location with better GPS reception. Check GPS-for-yaw configuration
Gyros inconsistent	Two gyros are inconsistent by at least 5 deg/sec	Reboot autopilot and hold vehicle still until gyro calibration completes. Allow autopilot to warm-up and reboot. If failure continues replace autopilot
Gyros not calibrated	Gyro calibration normally run at startup failed	Reboot autopilot and hold vehicle still until gyro calibration completes
Gyros not healthy	At least one gyro is not providing data	Reboot autopilot. If failure continues replace autopilot
Hardware safety switch	Hardware safety switch has not been pushed	Push safety switch (normally on top of GPS) or disable by setting BRD_SAFETY_DEFLT to zero and reboot autopilot
heater temp low (x < 45)	Board heater temp is below BRD_HEAT_TARG	Wait for board to heat up. Target temperature can be adjust using BRD_HEAT_TARG
In OSD menu	OSD is being configured	Complete OSD configuration. Check OSD configuration
Internal errors 0x%x l:%u %s	An internal error has occurred	Reboot the autopilot. Report error to the development team
Invalid FENCE_ALT_MAX value	FENCE_ALT_MAX must be positive	Increase FENCE_ALT_MAX
Invalid FENCE_ALT_MIN value	FENCE_ALT_MIN must be higher than -100	Increase FENCE_ALT_MIN
Invalid FENCE_MARGIN value	FENCE_MARGIN must be positive	Increase FENCE_MARGIN
Invalid FENCE_RADIUS value	FENCE_RADIUS must be positive	Increase FENCE_RADIUS
Logging failed	Logs could not be written. Maybe hardware failure	Reboot autopilot. Replace autopilot
Logging not started	Logs could not be written. Maybe hardware failure	Reboot autopilot. Replace autopilot
Main loop slow (xHz < 400Hz)	Autopilot’s CPU is overloaded	Wait to see if the error is temporary. Disable features or replace with a higher powered autopilot. Reduce SCHED_LOOP_RATE
Margin is less than inclusion circle radius	A circular fence has radius below FENCE_MARGIN	Increase the size of the circular fence involved or decrease FENCE_MARGIN
memory low for auxiliary authorisation	Autopilot has run out of memory	Disable features or replace with a higher powered autopilot
Missing mission item: do land start	Auto mission needs a DO_LAND_START command	Add a DO_LAND_START command to the mission or adjust the ARMING_MIS_ITEMS parameter
Missing mission item: land	Auto mission needs a LAND command	Add a LAND command to the mission or adjust the ARMING_MIS_ITEMS parameter
Missing mission item: RTL	Auto mission needs an RTL command	Add an RTL command to the mission or adjust the ARMING_MIS_ITEMS parameter
Missing mission item: takeoff	Auto mission needs a TAKEOFF command	Add a TAKEOFF command to the mission or adjust the ARMING_MIS_ITEMS parameter
Missing mission item: vtol land	Auto mission needs a VTOL_LAND command	Add a VTOL_LAND command to the mission or adjust the ARMING_MIS_ITEMS parameter
Missing mission item: vtol takeoff	Auto mission needs a VTOL_TAKEOFF command	Add a VTOL_TAKEOFF command to the mission or adjust the ARMING_MIS_ITEMS parameter
Mode channel and RCx_OPTION conflict	RC flight mode switch also used for an aux function	Change FLTMODE_CH (or MODE_CH for Rover) or RCx_OPTION to remove conflict
Mode requires mission	Attempting to arm in Auto mode but no mission	Arm in an other mode or create and upload an Auto mission
Motors Emergency Stopped	Motors emergency stopped	Release emergency stop. See auxiliary functions
Mount: check TYPE	Mount (aka camera gimbal) misconfiguration	Check MNT1_TYPE is valid. Check Gimbal configuration
Mount: not healthy	Mount is not communicating with autopilot	Check physical connection between autopilot and gimbal and check Gimbal configuration
Multiple SERIAL ports configured for RC input	RC misconfiguration	see Multiple Radio Control Receivers
No mission library present	Auto mission feature has been disabled	Custom build server was probably used to produce the firmware without auto missions. Rebuild with auto missions enabled
No rally library present	Rally point feature has been disabled	Custom build server was probably used to produce the firmware without rally point. Rebuild with Rally points included
No SD card	SD card is corrupted or missing	Format or replace SD card
No sufficiently close rally point located	Rally points are further than RALLY_LIMIT_KM	Move rally points closer to vehicle’s current location or increase RALLY_LIMIT_KM
OA requires reboot	Object avoidance config change requires reboot	Reboot autopilot. See Object Avoidance configuration
OpenDroneID: ARM_STATUS not available	OpenDroneID misconfiguration	see Remote ID configuration
OpenDroneID: operator location must be set	Operator location is not available	see Remote ID configuration
OpenDroneID: SYSTEM not available	OpenDroneID misconfiguration	see Remote ID configuration
OpenDroneID: UA_TYPE required in BasicID	OpenDroneID misconfiguration	see Remote ID configuration
OSD_TYPE2 not compatible with first OSD	OSD1 and OSD2 configurations are incompatible	Disable 2nd OSD (set OSD_TYPE2 to zero) or check OSD configuration
Param storage failed	Eeprom hardware failure	Check power supply or replace autopilot
parameter storage full	Eeprom storage full	Save params. Reset to defaults. Reload saved parameters.
PiccoloCAN: Servo x not detected	PiccoloCAN misconfiguration or servo issue	Check Currawong Velocity ESC setup instructions
Pin x disabled (ISR flood)	Sensor connected to GPIO pin is rapidly changing	Check sensor attached to specified pin
Pitch (RCx) is not neutral	RC transmitter’s pitch stick is not centered	Move RC pitch stick to center or repeat radio calibration
Pitch radio max too low	RC pitch channel max below 1700	Repeat the radio calibration procedure or increase RC2_MAX above 1700
Pitch radio min too high	RC pitch channel min above 1300	Repeat the radio calibration procedure or reduce RC2_MIN below 1300
PRXx: No Data	Proximity sensor is not providing data	Check proximity sensor physical connection and configuration
PRXx: Not Connected	Proximity sensor is not providing data	Check proximity sensor physical connection and configuration
Radio failsafe on	RC failsafe has triggered	Turn on RC transmitter or check RC failsafe configuration
Rangefinder x: Not Connected	Rangefinder is not providing data	Check rangefinder’s physical connection to autopilot and configuration
Rangefinder x: Not Detected	Rangefinder is not providing data	Check rangefinder’s physical connection to autopilot and configuration
RC calibrating	RC calibration is in progress	Complete the radio calibration procedure
RC not calibrated	RC calibration has not been done	Complete the radio calibration. RC3_MIN and RC3_MAX must have been changed from their default values (1100 and 1900), and for channels 1 to 4, MIN value must be 1300 or less, and MAX value 1700 or more.
RC not found	RC failsafe enabled but no RC signal	Turn on RC transmitter or check RC transmitters connection to autopilot. If operating with only a GCS, see Operation Using Only a Ground Control Station (GCS)
RCx_MAX is less than RCx_TRIM	RC misconfiguration	Adjust RCx_TRIM to be lower than RCx_MAX or repeat radio calibration
RCx_MIN is greater than RCx_TRIM	RC misconfiguration	Adjust RCx_TRIM to be higher than RCx_MIN or repeat radio calibration
RELAYx_PIN=y invalid	Relay misconfigured	RELAYx_PIN is set to an invalid value. Check Relay setup instructions
RELAYx_PIN=y, set SERVx_FUNCTION=-1	Relay misconfigured	Set SERVOx_FUNCTION to -1
RNGFNDx_PIN not set	Rangefinder misconfigured	Set RNGFNDx_PIN to a non-zero value. See rangefinder configuration
RNGFNDx_PIN=y invalid	Rangefinder misconfigured	RNGFNDx_PIN is set to an invalid value. Check rangefinder configuration
RNGFNDx_PIN=y, set SERVOx_FUNCTION=-1	Rangefinder misconfigured	Set SERVOx_FUNCTION to -1
Roll (RCx) is not neutral	RC transmitter’s roll stick is not centered	Move RC roll stick to center or repeat radio calibration
Roll radio max too low	RC roll channel max below 1700	Repeat the radio calibration procedure or increase RC1_MAX above 1700
Roll radio min too high	RC roll channel min above 1300	Repeat the radio calibration procedure or reduce RC1_MIN below 1300
RPMx_PIN not set	RPM sensor misconfigured	Check RPMx_PIN value. Check RPM setup instructions
RPMx_PIN=y invalid	RPM sensor misconfigured	RPMx_PIN is set to an invalid value. Check RPM setup instructions
RPMx_PIN=y, set SERVOx_FUNCTION=-1	RPM sensor misconfigured	Set SERVOz_FUNCTION to -1
Same Node Id x set for multiple GPS	DroneCan GPS configuration error	Check GPS1_CAN_NODEID and GPS2_CAN_NODEID are different. Set one to zero and reboot autopilot
Same rfnd on different CAN ports	Two rangefinders appearing on different CAN ports	Check USD1, TOFSensP, NanoRadar or Benewake setup instructions
Scripting: loaded CRC incorrect want: x	Script has incorrect CRC	Replace Lua script with expected version
Scripting: running CRC incorrect want: x	Script has incorrect CRC	Replace Lua script with expected version
Scripting: xxx failed to start	A Lua script failed to start	Autopilot out of memory or Lua script misconfiguration. See Lua scripts
Scripting: xxx out of memory	A Lua script ran out of memory	Increase SCR_HEAP_SIZE or check Lua script configuration
Servo voltage to low (Xv < 4.3v)	Servo rail voltage below 4.3V	Check power supply to rear servo rail
SERVOx_FUNCTION=y on disabled channel	PWM output misconfigured	SERVOx_FUNCTION is set for a servo output that has been disabled. See BLHeli setup
SERVOx_MAX is less than SERVOx_TRIM	PWM output misconfigured	Set SERVOx_TRIM to be lower than SERVOx_MAX
SERVOx_MIN is greater than SERVOx_TRIM	PWM output misconfigured	Set SERVOx_TRIM to be higher than SERVOx_MIN
temperature cal running	Temperature calibration is running	Wait until temp calibration completes or reboot autopilot
terrain disabled	Auto mission uses terrain but terrain disabled	Enable the terrain database (set TERRAIN_ENABLE = 1) or remove auto mission items that use terrain altitudes. For Copters also check RTL_ALT_TYPE.
Terrain out of memory	Autopilot has run out of memory	Disable features or replace with a higher powered autopilot
Throttle (RCx) is not neutral	RC transmitter’s throttle stick is too high	Lower throttle stick or repeat radio calibration
Throttle radio max too low	RC throttle channel max below 1700	Repeat the radio calibration procedure or increase RC2_MAX above 1700
Throttle radio min too high	RC throttle channel min above 1300	Repeat the radio calibration procedure or reduce RC1_MIN below 1300
Too many auxiliary authorisers	More than 3 external systems controlling arming	Check external authorisation system
vehicle outside fence	Vehicle is outside the fence	Move vehicle within the fence
VisOdom: not healthy	VisualOdometry sensor is not providing data	Check visual odometry physical connection and configuration
VisOdom: out of memory	Autopilot has run out of memory	Disable features or replace with a higher powered autopilot
VTOL Fwd Throttle iz not zero	RC transmitter’s VTOL Fwd throttle stick is high	Lower VTOL Fwd throttle stick or repeat radio calibration
waiting for terrain data	Waiting for GCS to provide required terrain data	Wait or move to location with better GPS reception
Yaw (RCx) is not neutral	RC transmitter’s yaw stick is not centered	Move RC yaw stick to center or repeat radio calibration
Yaw radio max too low	RC yaw channel max below 1700	Repeat the radio calibration procedure or increase RC2_MAX above 1700
Yaw radio min too high	RC yaw channel min above 1300	Repeat the radio calibration procedure or reduce RC1_MIN below 1300

Other Failure messages¶

Failsafes:¶

Any failsafe (RC, Battery, GCS,etc.) will display a message and prevent arming.

Barometer failures:¶

Baro not healthy : the barometer sensor is reporting that it is unhealthy which is normally a sign of a hardware failure.

Alt disparity : the barometer altitude disagrees with the inertial navigation (i.e. Baro + Accelerometer) altitude estimate by more than 1 meters. This message is normally short-lived and can occur when the autopilot is first plugged in or if it receives a hard jolt (i.e. dropped suddenly). If it does not clear the accelerometers may need to be calibrated or there may be a barometer hardware issue.

Compass failures:¶

Compass not healthy : the compass sensor is reporting that it is unhealthy which is a sign of a hardware failure.

Compass not calibrated : the compass(es) has not been calibrated. the COMPASS_OFS_X, _Y, _Z parameters are zero or the number or type of compasses connected has been changed since the last compass calibration was performed.

Compass offsets too high : the primary compass’s offsets length (i.e. sqrt(x^2+y^2+z^2)) are larger than 500. This can be caused by metal objects being placed too close to the compass. If only an internal compass is being used (not recommended), it may simply be the metal in the board that is causing the large offsets and this may not actually be a problem in which case you may wish to disable the compass check.

Check mag field : This can result from failing two different checks. First, the sensed magnetic field in the area is 35% higher or lower than the expected value. The expected length is 530 so it’s > 874 or < 185. Also, besides this rough check, when the vehicle’s position has been obtained (GPS lock), another check against the field strength predicted using the internal World Magnetic Field database is done with much tighter limits. If you are failing this, either the compass calibration has not calculated good offsets and calibration should be repeated, or your vehicle is near a large metallic or magnetic disturbance and will need to be relocated.

Compasses inconsistent : the internal and external compasses are pointing in different directions (off by >45 degrees). This is normally caused by the external compasses orientation (i.e. COMPASS_ORIENT parameter) being set incorrectly.

INS checks (i.e. Acclerometer and Gyro checks):¶

INS not calibrated: some or all of the accelerometer’s offsets are zero. The accelerometers need to be calibrated.

Accels not healthy: one of the accelerometers is reporting it is not healthy which could be a hardware issue. This can also occur immediately after a firmware update before the board has been restarted.

Accels inconsistent: the accelerometers are reporting accelerations which are different by at least 1m/s/s. The accelerometers need to be re-calibrated or there is a hardware issue.

Gyros not healthy: one of the gyroscopes is reporting it is unhealthy which is likely a hardware issue. This can also occur immediately after a firmware update before the board has been restarted.

Gyro cal failed: the gyro calibration failed to capture offsets. This is most often caused by the vehicle being moved during the gyro calibration (when red and blue lights are flashing) in which case unplugging the battery and plugging it in again while being careful not to jostle the vehicle will likely resolve the issue. Sensors hardware failures (i.e. spikes) can also cause this failure.

Gyros inconsistent: two gyroscopes are reporting vehicle rotation rates that differ by more than 20deg/sec. This is likely a hardware failure or caused by a bad gyro calibration.

Board Voltage checks:¶

Check Board Voltage: the board’s internal voltage is below 4.3 Volts or above 5.8 Volts.

If powered through a USB cable (i.e. while on the bench) this can be caused by the desktop computer being unable to provide sufficient current to the autopilot - try replacing the USB cable.

If powered from a battery this is a serious problem and the power system (i.e. Power Module, battery, etc) should be carefully checked before flying.

Parameter checks:¶

Ch7&Ch8 Opt cannot be same: Auxiliary Function Switches are set to the same option which is not permitted because it could lead to confusion.

Check FS_THR_VALUE: the radio failsafe pwm value has been set too close to the throttle channels (i.e. ch3) minimum.

Check ANGLE_MAX: the ANGLE_MAX parameter which controls the vehicle’s maximum lean angle has been set below 10 degrees (i.e. 1000) or above 80 degrees (i.e. 8000).

ACRO_BAL_ROLL/PITCH: the ACRO_BAL_ROLL parameter is higher than the Stabilize Roll P and/or ACRO_BAL_PITCH parameter is higher than the Stabilize Pitch P value. This could lead to the pilot being unable to control the lean angle in ACRO mode because the Acro Trainer stabilization would overpower the pilot’s input.

Battery/Power Monitor:¶

If a power monitor voltage is below its failsafe low or critical voltages or failsafe remaining capacity low or critical set points, this check will fail and indicate which set point it is below. It will also fail if these set points are inverted, ie critical point is higher than low point. See Battery Failsafe for Copter, Plane Failsafe Function for Plane, or Failsafes for Rover for more information on these.

In addition, minimum arming voltage and remaining capacity parameters for each battery/power monitor can be set, for example BATT_ARM_VOLT and BATT_ARM_MAH for the first battery, to provide a check that the battery is not only above failsafe levels, but also has enough capacity for operation.

Airspeed:¶

If an airspeed sensor is configured, and it is not providing a reading or failed to calibrate, this check will fail.

Airspeed not healthy

Logging:¶

Logging failed: Logging pre-armed was enabled but failed to write to the log.

No SD Card: Logging is enabled, but no SD card is detected.

Safety Switch:¶

Hardware safety switch: Hardware safety switch has not been pushed.

System:¶

Param storage failed: A check of reading the parameter storage area failed.

Internal errors (0xx): An internal error has occurred. Report to ArduPilot development team here

KDECAN Failed: KDECAN system failure.

DroneCAN Failed: DroneCAN system failure.

Mission:¶

See ARMING_MIS_ITEMS

No mission library present: Mission checking is enabled, but no mission is loaded.

No rally library present: Rally point checking is enabled, but no rally points loaded.

Missing mission item: xxxx: A required mission items is missing.

Rangefinder:¶

IF a rangefinder has been configured, a reporting error has occurred.

Disabling the Pre-arm Safety Check¶

Warning

Disabling pre-arm safety checks is not recommended. The cause of the pre-arm failure should be corrected before operation of the vehicle if at all possible. If you are confident that the pre-arm check failure is not a real problem, it is possible to disable a failing check.

Arming checks can be individually disabled by setting the ARMING_CHECK parameter to something other than 1. Setting to 0 completely removes all pre-arm checks. For example, setting to 4 only checks that the GPS has lock.

This can also be configured using Mission Planner:

Connecting your Autopilot to the Mission Planner
Go to Mission Planner’s Config/Tuning >> Standard Params screen
set the Arming Check drop-down to “Disabled” or one of the “Skip” options which more effectively skips the item causing the failure.
Push the “Write Params” button

Pre-Arm Safety Checks¶

Recognising which Pre-Arm Check has failed using the GCS¶

Other Failure messages¶

Failsafes:¶

Barometer failures:¶

Compass failures:¶

GPS related failures:¶

INS checks (i.e. Acclerometer and Gyro checks):¶

Board Voltage checks:¶

Parameter checks:¶

Battery/Power Monitor:¶

Airspeed:¶

Logging:¶

Safety Switch:¶

System:¶

Mission:¶

Rangefinder:¶

Disabling the Pre-arm Safety Check¶