The medical variant of the Mi-290 Taru has a texture glitch which prevents the rear ramp frame from being textured. This can be demonstrated by applying any texture to the helicopter, and looking at the edges of the rear ramp. I have taken a screenshot from the virtual arsenal garage to show the issue:

https://steamuserimages-a.akamaihd.net/ugc/921423854042549803/F3D544364B25287BC169F387AF90B4382CF2EABC/