[8.9" Kindle Fire HD Android Development] jjrizzelcincy:
i used this to root OS 8.5.1 http://xdaforums.com/showthread.php?t=1886460

and then i used fireflash http://xdaforums.com/showthread.php?t=2168512 and the images from Hashcode's 2nd bootloader post.

and downloaded the files from Hashcode's 2nd bootloader post

follow this and you should be good 1. Go to Hashcode's 2nd-bootloader thread

2. Download both the required files and move them to sdcard

3. Use ADB to make backups (optional)

4. Use fastboot to restore the images you backed up if there are issues

Step 3: Installation

You might have noticed that Hashcode made a pretty extensive thread to help you flash the bootloader, but another coder has since developed an automatic app to do all the work for you: FireFlash. Go ahead and download the .apk file. Move that file to the sdcard, and on the device, install it using "ES File Manager" (tap on that file) or "Easy Installer" (after it finishes scanning, select it and install), both found on the Amazon Appstore. You will then find it in the applications listing, go ahead and open it.

The first thing you notice is that there are spots to plug in files for different partitions. This is where those files from Hashcode come into play. Plug the freedom-boot.img into the boot partition space, plug the TWRP recovery.img into the recovery partition, and make sure to hit "apply stack". If you are NOT on the 8.1.4 bootloader (you'll see red letters warning you), then hit the check box next to that to flash the 8.1.4 bootloader, otherwise you'll see a red screen after you reboot. If you don't see that warning, you're fine, move on.

Check that "disable recovery auto update" box, leave everything else alone, unplug the cable, and hit flash (the first option). You will see a progress window, and just hit OK. Then, turn off the device. Now, when you turn it on, this is the way to enter recovery every time: the moment you turn it on, you'll see the yellow Kindle title. Immediately hold down the Volume Up button (leftmost from the power button) before it turns blue, and once it does, count to three in your head and let go and you'll see the TWRP splash logo. Once you're in TWRP, you're done. Just hit reboot, and everything's finished. Now you can browse the 8.9" Development forum for custom ROMs.

If you want to save space, you can now go ahead and delete all the files we just used; you no longer have a need for any of them. Keep FireFlash, though, because in the future you might want to update TWRP, then leave everything blank, plug the update image into the recovery partition and hit flash. Only use Hashcode's TWRP builds as of now, because he specifically altered those builds to work on the Kindle Fire HD 7" and 8.9" so the official ones on the TWRP site won't work. If you flash those (especially the "blaze" codename), you will brick the device, so don't do it!

Recap:

1. Download FireFlash and install on device using file manager or installer

2. Plug in the required files in the correct areas, and check the necessary checkboxes

3. Flash, and boot into TWRP to confirm successful installation of both 2nd-Bootloader and TWRP recovery,,,,,,,,i copied this info from this post so give a thanks to the guys who originally posted this guide http://xdaforums.com/showthread.php?t=2277105