Arming Sequence & Safety

SwiftingSpeed edited this page Aug 15, 2018 · 22 revisions

Switch arming

The AUX channel configured for arming will choose a default value that falls outside of the configured arm range (as configured in the "Modes" configurator tab), this value is either 1 "step" (25us) above or below the configured range. This is a safety feature to ensure the default value would not cause accidental arming.

Note that this default value is overwritten by the first values data from the receiver, therefore bad RX initial states or failsafe settings can still cause issues.

Arming Prevention

Betaflight 3.2 (and above) includes more detailed troubleshooting information for the case when a craft will not arm.

This information is available via:

  • the CLI
  • Betaflight OSD
  • beep patterns
  • Betaflight Configurator

Several of these conditions are to assist in preventing accidental arming via bad radio system configuration, unreliable/poor quality receivers and user mistakes.

These reasons for not arming are encoded as a set of flags (see runtime_config.h).


Flags can be viewed via the status command.

Some targets with limited flash space will only provide the hexadecimal representation of these flags, in which case the active flags must be derived from the armingDisableFlags_e enum in runtime_config.h (ensure the version of the file you are looking at matches that of your firmware).


When arming is attempted and fails, if a beeper is connected to the flight controller it will emit a warning signal indicating the most important (lowest number) reason why disarming is disabled.

The signal is as follows:

  • five short 'attention' beeps;
  • a number of long beeps (may be 0);
  • a number of short beeps with long intervals (may be 0).

The arming prevention condition that is active can be calculated as (5 * <number of long beeps>) + <number of short beeps>. For example:

  • 1 long and 2 short beeps = 7
  • 2 long beeps = 10

Description of arming prevention flags

What each flag means and what you should do to (probably) fix the issue.

This list should be kept up to date with the code in master (armingDisableFlags_e in src/main/fc/runtime_config.h) so can be used to find what flag corresponds to a certain index, however if you run an older version you'd have to check this manually as mentioned above.

Name Description Beep code Required Actions
3.2 3.3 3.4+
NOGYRO A gyro was not detected 1 1 1 You may have a hardware failure, if a previous firmware version works then it may be a firmware issue.
FAILSAFE Failsafe is active 2 2 2 Rectify the failure condition and try again.
RX LOSS(1) No valid receiver signal is detected 3 3 3 Your receiver is either faulty or has no link to the transmitter.
BAD RX(1) Your receiver has just recovered from receiver failsafe but the arm switch is on 4 4 4 Switch the arm switch off.
BOXFAILSAFE The 'FAILSAFE' switch was activated 5 5 5 See FAILSAFE
RUNAWAY Runway Takeoff Prevention has been triggered 6 6 Disarm to clear this condition.
THROTTLE Throttle channel is too high 6 7 7 Lower throttle below min_check.
ANGLE Craft is not level (enough) 7 8 8 Level craft to within small_angle degrees (default 25).
BOOT GRACE Arming too soon after power on 8 9 9 Wait until pwr_on_arm_grace seconds (default 5) have elapsed.
NO PREARM Prearm switch is not activated or prearm has not been toggled after disarm 9 10 10 Toggle the prearm switch.
LOAD System load is too high for safe flight 10 11 11 Revisit configuration and disable features.
CALIB Sensor calibration is still ongoing 11 12 12 Wait for sensor calibration to complete.
CLI CLI is active 12 13 13 Exit the CLI.
CMS CMS (config menu) is Active - over OSD or other display 13 14 14 Exit the CMS (or OSD menu).
OSD OSD menu is active 14 15 15 Exit OSD menu.
BST A Black Sheep Telemetry device (TBS Core Pro for example) disarmed and is preventing arming 15 16 16 Refer to the manual for your hardware.
MSP MSP connection is active, probably via Betaflight Configurator 16 17 17 Terminate the Betaflight Configurator connection (disconnect).
PARALYZE Paralyze mode has been activated 18 Power cycle/reset FC board.
GPS GPS rescue mode is configured but required number of satellites has not been fixed 19 Wait for GPS fix or disable GPS rescue mode.
ARM SWITCH Arm switch is in an unsafe position 17 18 20 Toggle the arm switch to arm.
(1) This may appear on the Betaflight OSD during flight, take it as a sign that your radio system is either faulty or you are flying at the edge of your range. Treat it the same you would an "RSSI critically low" warning.


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