PX4 User Guide
  • Introduction
  • Getting Started
    • Basic Concepts
    • Vehicles/Frames
    • Flight Controllers
    • Sensors
    • Radio Systems
    • Flight Modes
    • Vehicle Status Notifications
      • LED Meanings
      • Tune/Sound Meanings
      • Preflight Checks
    • Payloads & Cameras
    • Flight Reporting
  • Basic Assembly
    • Mounting the Flight Controller
    • Mounting the GPS/Compass
    • Vibration Isolation
    • Cable Wiring
    • CUAV Pixhawk V6X Wiring QuickStart
    • CUAV V5+ Wiring Quickstart
    • CUAV V5 nano Wiring Quickstart
    • Holybro Pixhawk 6C Wiring Quickstart
    • Holybro Pixhawk 6X Wiring Quickstart
    • Holybro Pixhawk 5X Wiring Quickstart
    • Holybro Pixhawk 4 Wiring Quickstart - Discontinued
    • Holybro Pixhawk 4 Mini Wiring Quickstart - Discontinued
    • Holybro Durandal Wiring Quickstart
    • Holybro Pix32 v5 Wiring Quickstart
    • Cube Wiring Quickstart
    • Pixracer Wiring Quickstart
    • mRo (3DR) Pixhawk Wiring Quickstart
  • Standard Configuration
    • Firmware
    • Airframe
    • Sensor Orientation
    • Compass
    • Gyroscope
    • Accelerometer
    • Airspeed
    • Level Horizon Calibration
    • Radio Setup
    • Joystick Setup
    • Flight Modes
    • Battery
    • Safety
      • Failsafe Simulation
    • ESC Calibration
    • Actuators
    • Autotune
  • Vehicle Types & Setup
    • Multicopters
      • Multicopter Config/Tuning
        • MC Filter/Control Latency Tuning
        • MC PID Tuning (Manual/Basic)
        • MC PID Tuning Guide (Manual/Advanced)
        • MC Setpoint Tuning (Trajectory Generator)
          • MC Jerk-limited Type Trajectory
        • Multicopter Racer Setup
      • X500 v2 (Pixhawk 6C)
      • X500 v2 (Pixhawk 5X)
      • X500 (Pixhawk 4)
      • S500 V2 (Pixhawk 4)
      • DJI F450 (CUAV v5+)
      • DJI F450 (CUAV v5 nano)
      • QAV250 (Pixhawk4 Mini) - Discontinued
      • DJI F450 + RTK (Pixhawk 3 Pro)
      • QAV250 (Pixhawk Mini)
      • QAV-R 5" Racer (Pixracer)
      • Omnicopter
    • Planes
      • Fixed Wing Config/Tuning
        • Fixedwing PID Tuning Guide
        • Fixedwing Advanced Tuning Guide
        • Fixedwing Trimming Guide
      • Reptile Dragon 2 (ARK6X)
      • Turbo Timber Evolution (Pixhawk 4 Mini)
      • Wing Wing Z84 (Pixracer)
    • VTOL
      • VTOL Config/Tuning
        • QuadPlane Configuration
        • Back-transition Tuning
        • VTOL w/o Airspeed Sensor
        • VTOL Weather Vane
      • Standard VTOL
        • FunCub QuadPlane (Pixhawk)
        • Ranger QuadPlane (Pixhawk)
        • Falcon Vertigo QuadPlane (Dropix)
      • Tailsitter VTOL
        • Build: TBS Caipiroshka Tailsitter Build (Pixracer)
      • Tiltrotor VTOL
        • Build: Convergence Tiltrotor (Pixfalcon)
    • Airships (experimental)
    • Autogyros (experimental)
      • ThunderFly Auto-G2 (Holybro pix32)
    • Balloons (experimental)
    • Helicopter (experimental)
      • Helicopter Config/Tuning
    • Rovers (experimental)
      • Traxxas Stampede
    • Submarines (experimental)
      • BlueROV2
    • Airframes Reference
  • Flying
    • First Flight Guidelines
    • Flying 101
    • Missions
      • Package Delivery Mission
    • GeoFence
    • Safety Point Planning
    • Flight Modes
      • Position Mode (MC)
      • Altitude Mode (MC)
      • Manual/Stabilized Mode (MC)
      • Acro Mode (MC)
      • Orbit Mode (MC)
      • Position Mode (FW)
      • Altitude Mode (FW)
      • Stabilized Mode (FW)
      • Acro Mode (FW)
      • Manual Mode (FW)
      • Takeoff Mode
      • Land Mode
      • Return Mode
      • Hold Mode
      • Mission Mode
      • Follow Me Mode
      • Offboard Mode
    • Terrain Following/Holding
  • Flight Log Analysis
    • Log Analysis using Flight Review
    • Log Analysis using PlotJuggler
  • Advanced Configuration
    • Finding/Updating Parameters
    • Full Parameter Reference
    • ECL/EKF Overview & Tuning
    • Flight Termination Configuration
    • Bootloader Flashing onto Betaflight Systems
    • Land Detector Configuration
    • Prearm/Arm/Disarm Configuration
    • IMU Factory Calibration
    • Sensor Thermal Compensation
    • Compass Power Compensation
    • Advanced Controller Orientation
    • Static Pressure Buildup
    • Serial Port Configuration
    • MAVLink Telemetry (OSD/GCS)
    • PX4 Ethernet Setup
    • Bootloader Update
  • Hardware (Drones&Parts)
    • Complete Vehicles
      • ModalAI Starling
      • PX4 Vision Kit
      • MindRacer BNF & RTF
        • MindRacer 210
        • NanoMind 110
      • Holybro Kopis 2
      • Bitcraze Crazyflie 2.1
    • Flight Controllers (Autopilots)
      • Pixhawk Series
        • Silicon Errata
      • Pixhawk Standard Autopilots
        • CUAV Pixhawk V6X (FMUv6X)
        • Holybro Pixhawk 6X (FMUv6X)
        • Holybro Pixhawk 6C (FMUv6C)
        • Holybro Pixhawk 6C Mini(FMUv6C)
        • Holybro Pix32 v6 (FMUv6C)
        • Holybro Pixhawk 5X (FMUv5X)
        • Holybro Pixhawk 4 (FMUv5) - Discontinued
        • Holybro Pixhawk 4 Mini (FMUv5) - Discontinued
        • Drotek Pixhawk 3 Pro (FMUv4pro)
        • mRo Pixracer (FMUv4)
        • Hex Cube Black (FMUv3)
        • mRo Pixhawk (FMUv3)
        • Holybro Pixhawk Mini (FMUv3) - Discontinued
      • Manufacturer-Supported Autopilots
        • AirMind MindPX
        • AirMind MindRacer
        • ARK Electronics ARKV6X
        • CUAV X7
        • CUAV Nora
        • CUAV V5+ (FMUv5)
        • CUAV V5 nano (FMUv5)
        • CUAV Pixhack v3 (FMUv3)
        • CubePilot Cube Orange+ (CubePilot)
        • CubePilot Cube Orange (CubePilot)
        • CubePilot Cube Yellow (CubePilot)
        • Holybro Kakute H7v2
        • Holybro Kakute H7mini
        • Holybro Kakute H7
        • Holybro Durandal
        • Holybro Pix32 v5
        • ModalAI Flight Core v1
        • ModalAI VOXL Flight
        • ModalAI VOXL 2
        • mRobotics-X2.1 (FMUv2)
        • mRo Control Zero F7)
        • NXP RDDRONE-FMUK66 FMU
        • Sky-Drones AIRLink
        • SPRacing SPRacingH7EXTREME
        • ThePeach FCC-K1
        • ThePeach FCC-R1
      • Experimental Autopilots
        • BeagleBone Blue
        • Raspberry Pi 2/3 Navio2
        • Raspberry Pi 2/3/4 PilotPi
          • PilotPi with Raspberry Pi OS
          • PilotPi with Ubuntu Server
      • Discontinued Autopilots/Vehicles
        • Drotek Dropix (FMUv2)
        • Omnibus F4 SD
        • BetaFPV Beta75X 2S Brushless Whoop
        • Bitcraze Crazyflie 2.0
        • Aerotenna OcPoC-Zynq Mini
        • CUAV v5
        • Holybro Kakute F7 (Discontinued)
        • Holybro Pixfalcon
        • Holybro pix32 (FMUv2)
        • mRo AUAV-X2
        • 3DR Pixhawk 1
        • Snapdragon Flight
        • Intel® Aero RTF Drone (Discontinued)
      • Pixhawk Autopilot Bus (PAB) & Carriers
        • ARK Electronics Pixhawk Autopilot Bus Carrier
    • Flight Controller Peripherals
      • ADSB/FLARM (Traffic Avoidance)
      • Air Traffic Avoidance: ADSB/FLARM
      • Air Traffic Avoidance: UTM
      • Airspeed Sensors
        • TFSlot Airspeed Sensor
      • Barometers
      • Camera
      • Distance Sensors (Rangefinders)
        • Lightware SFxx Lidar
        • Ainstein US-D1 Standard Radar Altimeter
        • LeddarOne Lidar
        • Benewake TFmini Lidar
        • Lidar-Lite
        • TeraRanger
        • Lanbao PSK-CM8JL65-CC5
        • Avionics Anonymous Laser Altimeter UAVCAN Interface
      • ESCs & Motors
        • PWM ESCs and Servos
        • DShot ESCs
        • OneShot ESCs and Servos
        • DroneCAN ESCs
          • Zubax Telega
          • PX4 Sapog ESC Firmware
            • Holybro Kotleta
            • Zubax Orel
        • VESC
      • TBS Crossfire (CRSF) Telemetry
      • FrSky Telemetry
      • Gimbal (Mount) Configuration
      • GPS/Compass
        • ARK GPS
        • Holybro DroneCAN M8N GPS
        • LOCOSYS Hawk A1 GNSS
        • Hex Here2
        • Holybro M8N & M9N GPS
        • Sky-Drones SmartAP GPS
      • Grippers
        • Servo Gripper
      • Optical Flow
        • ARK Flow
        • PMW3901
        • PX4FLOW (Deprecated)
      • Precision Landing
      • Parachute
      • Power Modules/PDB
        • CUAV HV pm
        • CUAV CAN PMU
        • Holybro PM02
        • Holybro PM07
        • Holybro PM06 V2
        • Holybro PM02D (digital)
        • Holybro PM03D (digital)
        • Pomegranate Systems Power Module
        • Sky-Drones SmartAP PDB
      • Satellite Coms (Iridium/RockBlock)
      • Telemetry Radios
        • SiK Radio
          • RFD900 (SiK) Telemetry Radio
          • HolyBro (SIK) Telemetry Radio
        • Telemetry Wifi
          • ESP8266 WiFi Module
          • ESP32 WiFi Module
          • 3DR Telemetry Wifi (Discontinued)
        • Microhard Serial Telemetry Radio
          • ARK Electron Microhard Serial Telemetry Radio
          • Holybro Microhard P900 Telemetry Radio
        • CUAV P8 Telemetry Radio
        • HolyBro XBP9X - Discontinued
      • RTK GPS
        • ARK RTK GPS
        • RTK GPS Heading with Dual u-blox F9P
        • CUAV C-RTK
        • CUAV C-RTK2 PPK/RTK GNSS
        • CUAV C-RTK 9Ps
        • Femtones MINI2 Receiver
        • Freefly RTK GPS
        • Holybro H-RTK-F9P
        • Holybro H-RTK-M8P
        • Holybro H-RTK Unicore UM982 GPS
        • Locosys Hawk R1
        • Locosys Hawk R2
        • Septentrio AsteRx-RIB
        • Septentrio mosaic-go
        • Trimble MB-Two
        • CubePilot Here+ (Discontined)
      • Remote ID
      • Smart Batteries
        • Rotoye Batmon Battery Smartification Kit
      • Tachometers (Revolution Counters)
        • ThunderFly TFRPM01 Tachometer Sensor
      • I2C Peripherals
        • I2C bus accelerators
        • TFI2CADT01 I2C address translator
      • CAN Peripherals
      • DroneCAN Peripherals
        • PX4 DroneCAN Firmware
        • ARK CANnode
    • Companion Computers
      • Pixhawk + Companion Setup
        • RasPi Pixhawk Companion
      • Companion Computer Peripherals
      • Holybro Pixhawk RPI CM4 Baseboard
      • Auterion Skynode
      • Computer Vision
        • Obstacle Avoidance
        • Safe Landing
        • Collision Prevention
        • Path Planning Interface
        • Motion Capture (MoCap)
        • Visual Inertial Odometry (VIO)
          • Realsense T265 Tracking Camera (VIO)
      • Video Streaming
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    • Hardware
      • Flight Controller Reference Design
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        • NuttX Board Porting Guide
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      • Airframes
        • Adding a New Airframe
      • Device Drivers
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        • I2C Bus
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          • Port-Configurable Serial Drivers
      • RTK GPS (Integration)
    • Middleware
      • uORB Messaging
      • uORB Graph
      • uORB Message Reference
        • ActionRequest
        • ActuatorArmed
        • ActuatorControlsStatus
        • ActuatorMotors
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        • DifferentialPressure
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        • EstimatorEventFlags
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On this page
  • EKF Preflight Checks/Errors
  • Other Parameters
  1. Getting Started
  2. Vehicle Status Notifications

Preflight Checks

PreviousTune/Sound MeaningsNextPayloads & Cameras

Last updated 1 year ago

PX4 performs a number of preflight sensor quality and estimator checks to determine if there is a good enough position estimate to arm and fly the vehicle (these checks are controlled by the parameters).

:::tip Any preflight errors are reported in QGroundControl as PREFLIGHT FAIL messages. The estimator_status.gps_check_fail_flags message also shows which GPS quality checks are failing. :::

The sections below list the errors, their likely causes and solutions, and any parameters that affect how the preflight checks are run.

EKF Preflight Checks/Errors

The following errors (with associated checks and parameters) are reported by the (and propagate to QGroundControl):

PREFLIGHT FAIL: EKF HGT ERROR

  • This error is produced when the IMU and height measurement data are inconsistent.

  • Perform an accel and gyro calibration and restart the vehicle. If the error persists, check the height sensor data for problems.

  • The check is controlled by the parameter.

PREFLIGHT FAIL: EKF VEL ERROR

  • This error is produced when the IMU and GPS velocity measurement data are inconsistent.

  • Check the GPS velocity data for un-realistic data jumps. If GPS quality looks OK, perform an accel and gyro calibration and restart the vehicle.

  • The check is controlled by the parameter.

PREFLIGHT FAIL: EKF HORIZ POS ERROR

  • This error is produced when the IMU and position measurement data (either GPS or external vision) are inconsistent.

  • Check the position sensor data for un-realistic data jumps. If data quality looks OK, perform an accel and gyro calibration and restart the vehicle.

  • The check is controlled by the parameter.

PREFLIGHT FAIL: EKF YAW ERROR

  • This error is produced when the yaw angle estimated using gyro data and the yaw angle from the magnetometer or external vision system are inconsistent.

  • Check the IMU data for large yaw rate offsets and check the magnetometer alignment and calibration.

  • The default value of 0.5 allows the differences between the navigation yaw angle and magnetic yaw angle (magnetometer or external vision) to be no more than 50% of the maximum tolerated by the EKF and provides some margin for error increase when flight commences.

  • It can fail if the yaw gyro has a large offset or if the vehicle is moved or rotated in the presence of a bad magnetic interference or magnetometer calibration.

PREFLIGHT FAIL: EKF HIGH IMU ACCEL BIAS

The EKF IMU acceleration bias is the difference between the measured acceleration reported by the IMU sensor and the expected acceleration reported by the EKF2 estimator (which fuses position and/or velocity data from a number of sources, including the IMU, GNSS, flow sensors etc.). This bias may change when the sensor is turned on (“turn-on bias”) and over time due to noise and temperature differences (“in-run bias”). The number should generally be very small (near zero), indicating that measurements from different sources all agree on the acceleration.

The warning indicates that the bias is higher than some arbitrary threshold (the vehicle will not be allowed to take off). It is most likely a sign that accelerometer or thermal calibration are required:

  • If you still get the warning after thermal calibration (or you can't perform thermal calibration):

    • Verify that the issues do not come from the sensor or autopilot hardware:

      • The easiest way to do this is to test the same frame/sensors with another autopilot.

    • Attempt to change the accelerometer bias learning tuning parameters.

Increasing the parameters will make the autopilot less likely to detect an anomaly and can modify the stability of the estimator. However it may be required if there are problems with the sensor that cannot be fixed by other means (i.e you can tune the EKF for better performance, but there is no way you can calibrate the accelerometer "better").

:::warning Tuning these parameters is a last resort. It should only be attempted if you have data showing it will improve the performance of the estimator. :::

Parameter
Description

The maximum bias value that the EKF is allowed to estimate (above this value the bias will be clipped and EKF will attempt to reset itself, possibly even switching to a more healthy EKF with a working IMU in a multi-EKF system). The autopilot will report a “high accel bias” if the estimated bias exceeds 75% of this parameter during a preflight check and prevent takeoff. The current value of 0.4m/s2 is already quite high and increasing it would make the autopilot less likely to detect an issue.

Initial bias uncertainty (if perfectly calibrated, this is related to the “turn-on bias” of the sensor). Some users might want to reduce that value if they know that the sensor is well calibrated and that the turn-on bias is small.

The expected “in-run bias” of the accelerometer or “how fast do we expect the bias to change per second”. By default, this value is large enough to include the drift due to a temperature change. If the IMU is temperature calibrated, the user might want to reduce this parameter.

The maximum acceleration at which the estimator will try to learn an acceleration bias. This is to prevent the estimator from learning a bias due to non-linearity and scale factor errors. (Almost no user should need to change that parameter except if they really know what they are doing).

PREFLIGHT FAIL: EKF HIGH IMU GYRO BIAS

  • This error is produced when the IMU gyro bias estimated by the EKF is excessive.

  • Excessive in this case means that the bias estimate exceeds 10deg/s (half the configured limit, which is hardcoded to 20deg/s).

PREFLIGHT FAIL: ACCEL SENSORS INCONSISTENT - CHECK CALIBRATION

  • This error message is produced when the acceleration measurements from different IMU units are inconsistent.

  • This check only applies to boards with more than one IMU.

PREFLIGHT FAIL: GYRO SENSORS INCONSISTENT - CHECK CALIBRATION

  • This error message is produced when the angular rate measurements from different IMU units are inconsistent.

  • This check only applies to boards with more than one IMU.

PREFLIGHT FAIL: COMPASS SENSORS INCONSISTENT - CHECK CALIBRATION

  • This error message is produced when the difference in measurements from different compass sensors is too great.

  • It indicates bad calibration, orientation or magnetic interference.

  • This check only applies to when more than one compass/magnetometer is connected.

PREFLIGHT FAIL: EKF INTERNAL CHECKS

  • This error message is generated if the innovation magnitudes of either the horizontal GPS velocity, magnetic yaw, vertical GPS velocity or vertical position sensor (Baro by default but could be range finder or GPS if non-standard parameters are being used) are excessive. Innovations are the difference between the value predicted by the inertial navigation calculation and measured by the sensor.

  • Users should check the innovation levels in the log file to determine the cause. These can be found under the ekf2_innovations message. Common problems/solutions include:

    • IMU drift on warmup. May be resolved by restarting the autopilot. May require an IMU accel and gyro calibration.

    • Adjacent magnetic interference combined with vehicle movement. Resolve my moving vehicle and waiting or re-powering.

    • Bad magnetometer calibration combined with vehicle movement. Resolve by recalibrating.

    • Initial shock or rapid movement on startup that caused a bad inertial nav solution. Resolve by restarting the vehicle and minimising movement for the first 5 seconds.

Other Parameters

The following parameters also affect preflight checks.

COM_ARM_WO_GPS

  • 1 (default): Arming is allowed without a position estimate for flight modes that do not require position information (only).

  • 0: Arming is allowed only if EKF is providing a global position estimate and EFK GPS quality checks are passing

The check is controlled by the parameter

If you sometimes get the warning: .

If you get regularly get the warning: Perform a .

Alternatively, all accelerometers across a number of bench test runs with 6: Sensor comparison enabled in .

The check is controlled by the parameter.

The check is controlled by the parameter.

The check is controlled by the parameter.

The parameter controls whether or not arming is allowed without a global position estimate.

re-calibrate the accelerometer
thermal calibration
in the logs
EKF
log and compare
COM_ARM_
COM_ARM_EKF_HGT
COM_ARM_EKF_VEL
COM_ARM_EKF_POS
COM_ARM_EKF_YAW
SDLOG_PROFILE
COM_ARM_IMU_ACC
COM_ARM_IMU_GYR
COM_ARM_MAG_ANG
COM_ARM_WO_GPS
EKF2_ABL_LIM
EKF2_ABIAS_INIT
EKF2_ACC_B_NOISE
EKF2_ABL_ACCLIM