Translations:OpenTX 2.2/27/en
From Spirit System Manual
To enter the bootloader, press and hold two Trims (for Aileron stick and Rudder stick) so that you will push them to the center. At the same time turn on the Transmitter. Transmitter will boot up in the special bootloader mode where you can perform the Firmware Upgrade without need of the computer. This mode should be always accessible so in any problem, you can still flash the old firmware.
