Yes it is possible to flash it using fastboot.
- You need to compile Static firmware image using SDK (make menu config > target images > trb14x static image)
- Once you finish compiling static image, you will be able to find it in SDK folder bin/targets/mdm9x07/generic/tltFws/
- Extract the compiled image and you should find root and kernel files inside.
- Download fastboot drivers to your PC.
- Plug your device and enter fastboot mode (hold reset button and plug power source while holding for few seconds)
- Check if your device entered fastboot mode:
If your device is in fastboot mode, you get output from this command. After that enter these commands
sudo fastboot flash boot_a kernel
sudo fastboot flash boot_b kernel
sudo fastboot rootfs_a root
sudo fastboot rootfs_b root
sudo fastboot reboot
kernel and root are full file paths to these files from your active directory.