Then it's all how you're saving these files.
You have a file in RGB mode, and you have to work in RGB mode. Do some work, whatever, create a new layer, paint bucket fill it with white (as a test). Then save the file as a PSD. After saving, flatten all the layers (layer > flatten image) then go to mode > indexed, select adaptive, 8-bit, Okay. Then Save As... and choose BMP from the drop down box. Name it exactly what the other file is called (the original bmp file) and click "Yes" when it asks you to overwrite, THEN click "Windows, 8bit," and leave un-checked the "compressed" option at the bottom. Then close photoshop (do not save if it asks, you already did), and start up AH. You SHOULD have an all-white aircraft now. Or, all white on the parts that used that bmp file.